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Evolution of Morphogenetic Processes in the Orthoamphisiellidae N. Fam., Oxytrichidae, and Parakahliellidae N. Fam., and Their Depiction Using a Computer Method (Ciliophora, Hypotrichida)

ABSTRACT. Forty detailed descriptions of divisional morphogenesis of protargol stained specimens were analyzed to establish a natural classification for the several hypotrich genera involved. Symbols were created for homologous interphase characters and morphogenetic processes and added to schematized computer drawings of the interphase cortical pattern, showing in one image the interphase and its morphogenesis. This method reveals genealogically linked relationships, correlated complex morphogenetic processes and their evolutionary transformation and gives a standardized account of known morphogenetic processes. Three monophyletic groups with their supposed ancestors are recognized, viz. Orthoamphisiellidae n. fam. and the two sister groups Oxytrichidae Ehrenberg,1838 and Parakahliellidae n. fam. Species presently assigned to the Oxytrichidae are highly evolved species of the two sister groups which separates the species presently assigned to the Oxytrichidae and Stylonychia into two phylogenetic lineages. The three monophyletic groups are separated by complex early morphogenetic anlagen developments in the two rightmost ventral cirral rows. These cirral rows are generated in the Oxytrichidae and the Parakahliellidae by "neokinetal" anlagen developments. In contrast, the Orthoamphisiellidae develop these two cirral rows by usual "within" anlagen. The two sister groups are separated from each other by generating "neokinetal 3" anlagen and long primary primordia in the Oxytrichidae and "neokinetal 1" anlagen and separate primary primordia in the Parakahliellidae. Dorsomarginal kineties develop in the Parakahliellidae and highly evolved Oxytrichidae. Dorsal kineties develop in all groups from not more than three within anlagen. The left fronto-ventral field evolved independently from evolutionary changes in the two rightmost ventral cirral rows. The Amphisiellidae and the Kahliellidae are junior synonyms of the Oxytrichidae. Suggested for Stylonychia pustulata and S. vorax are locations in Clara n. g. as Clara pustulata and C. vorax (new combinations). Results are in accordance with those obtained from molecular techniques.

Supplementary key words. Amphisiellidae, anlagen development, Clara, Kahliellidae, long primary primordia, monophyly, natural system, neokinetal, phylogeny, transformation series.

ALL the reasons for using ontogenetic data in reconstructing protozoan phylogenies and for research into ciliate morphogenesis are given in one study, to which nothing can be added [12]. Since that work several studies have been published reconstructing the phylogeny and evolution of groups of hypotrich ciliates using morphogenetic data [8, 9, 18, 21, 23, 62, 68, 69, 73]. Recently, the Kahliellidae were redefined by using, defining and terming the complex neokinetal anlagen developments (several species which are presently assigned to the Kahliellidae are considered to belong to the new family Parakahliellidae; [19]). However, the fundamental meaning of the early morphogenetic anlagen developments revealed now by the computer drawings in the present paper have not been recognized yet. Two seemingly independent anlagen generated in the Parakahliellidae are in fact anlagen-parts of one complex and consistent anlagen formation termed neokinetal 1; in contrast, a neokinetal 3 anlage develops in one part. This method of using the basically different morphogenetic anlagen developments recognizable only in early stages of division is refined and sustained in the present paper leading to results which are in accordance with the relevant studies using molecular techniques. These results show that the Oxytrichidae are not a cohesive phylogenetic group, Stylonychia mytilus and Stylonychia pustulata + S. vorax belong to different phylogenetic lineages and Stylonychia pustulata + S. vorax is closely related to Onychodromus quadricornutus being within the same phylogenetic group [55, 56].
The Oxytrichidae have been considered a monophyletic group for a long time, because they possess very few cirri and in some species some of those cirri form similar patterns. This pattern, which is obviously evolutionarily very successful, originates nevertheless at least from two phylogenetic lineages, as shown in the present paper. This pattern is the result of transformation series from lowly evolved Oxytrichidae and Parakahliellidae to their highly evolved state, and this pattern is therefore not an autapomorphy of a monophyletic group. In a recent study, this traditional oxytrichid pattern has been used on a group of highly evolved hypotrichs with few cirri, defining two monophyletic groups within the traditional family Oxytrichidae. In this study, most hypotrichs with many cirri (i. e. lowly evolved hypotrichs) are not considered. Thus, the decisive morphogenetic processes and their transformation which link lowly and highly evolved species are not recognized (see Comparison with recent studies; [5]).

Studies of divisional morphogenesis of hypotrich ciliates from literature with detailed descriptions of early stages of morphogenetic processes were analyzed and used for comparison. Eight of these descriptions were entirely or mainly produced in my private laboratory [19, 22, 23]. Few descriptions of divisional morphogenesis which are not clearly described in the decisive processes could not be considered in the present paper. No data from literature concerning morphogenetic processes were found that contradict the basic findings of the present paper. Symbols were created on a Macintosh computer for characters that can be recognized in interphase (e. g. the pattern formed by cirri and cilia) and those characters which are not or only indirectly recognizable in interphase (e. g. many morphogenetic processes).
The schematized drawings can be carried out efficiently only with a computer drawing program, as has been done. Computer programs like PAUP are not used since the phylogeny which is suggested in the present paper is based only on three characters and their states.
General description to Fig. 4--42. Symbols are described in Fig. 1. The legends to the figures describe mainly evolutionary changes from one species to another and unique or rare (morphogenetic) characters. More information about these species, for instance (former) assignment, closely related species and additional and ambiguous data from literature is given in Results and Discussion. Definitions are given below.
The computer drawing on the left side of each figure shows the schematized cortical pattern of the interphase individual and shows also the symbols that indicate the morphogenetic processes by which this cortical pattern is generated during divisional morphogenesis . Modified, original drawings from protargol stained specimens from literature are placed on the right side of the computer drawings. Lines and numbers indicate cirral rows and anlagen (e. g. Fig. 18 row 1--5, 7, L1), except for the rightmost ventral cirral row in the sister groups Oxytrichidae and Parakahliellidae. In these two groups the rightmost ventral row does not generate an anlage, and therefore the number stands only for the cirral row (Fig. 18 row 6). Lines which protrude from the posteriormost cirrus indicate long primary primordia developments (see below). Lines and numbers are identical in the original drawings and in the computer drawings. The anterior anlagen symbol in each row indicates the anlage for the future proter, the posterior one for the future opisthe (except for the neokinetal 3 anlage, which generates cirral rows for proter and opisthe; Fig. 1 f; Fig. 18 row 5). The boxes of the within anlagen symbols (Fig. 1a, b) and the boxes of the neokinetal anlagen symbols (Fig. 1 e, f) are placed in the computer drawings with their anterior edge touching the cirrus which is the first or only cirrus to participate in anlagen formation. The shape of the other cirri, located posterior or anterior of the anlagen symbol, indicates whether they also participate in anlagen formation: square cirri participate, rounded off cirri do not participate (Fig. 1 h--k). The within anlagen symbols (Fig. 1 a--c) are placed either exactly within a cirral row or more or less to the right or left of it, according to the developments shown in the original studies. Anlage 1 for proter contains no anlagen symbol, because it usually develops from the disaggregating undulating membranes. Anlagen generated by the oral primordium are indicated by boxes connected to the oral primordium symbol (Fig. 1 r). Connected symbols indicate common development (Fig. 17, 18 row 5 - neokinetal anlage - opisthe's anlage 4 - oral primordium). Dorsal kineties are indicated in the computer drawings without numbers but by lines and basal body pairs. Split dorsal kineties are indicated by their characteristically morphogenetic pattern (Fig. 14 between row 7 and the other two dorsal kineties; see below).
Missing symbols in the computer drawings usually indicate missing information in the original description.

Fig. 1. Symbols used in Fig. 4--42. a. "Within" anlagen mainly of short cirral rows and dorsal kineties whose direction of development is not certain. b. Within anlagen development in long cirral rows, indicating the main direction of development by an arrowhead. c. Within anlagen development, indicating a neokinetal 5 (N5) development in which the new row develops parallel to the old row. d. "De novo" anlagen development. e. "Neokinetal 1" (N1) anlagen development. This symbol is composed of two anlagen-parts, the anterior part indicates developments for the proter and the posterior part for the opisthe. f. "Neokinetal 3" (N3) anlagen development. g. Dorsomarginal kinety anlagen development. h. Used (active) cirri, which disaggregate while the new cirri are formed during morphogenesis and their basal bodies most likely contribute to the forming of new cirri. i. Distinctly enlarged used cirri. j. Unused (inactive) cirri, which do not disaggregate while the new cirri are formed. k. Distinctly enlarged unused cirri. l. Old (parental) cirri, which are passed on from a former generation by a neokinetal wave [19]. m. Dorsomarginal kinety. n. Old (parental) dorsomarginal kinety. Its displacement in the next generation(s) is indicated by arrows. o. Dorsal kinety. p. Adoral membranelles. q. Endoral and paroral membrane (undulating membranes). r. Field of basal bodies, usually oral primordium that generates opisthe's adoral membranelles and usually also opisthe's anlagen 1--3. s. Arrowheads and arrows indicate migration or displacement. t. Numbers indicate cirral rows and usually also their anlagen. u. Numbers in italic indicate anlagen for future cirral rows generated by N1 or N3 anlagen development. v. Cirral rows left of adoral membranelles. w. Right marginal row. x. Numbers of cilia cirri and adoral membranelles, if these numbers are smaller in the computer drawing then the numbers given in the original description. y. Number of macronuclear nodules on average.

Fig. 2. Phylogenetic relationship within three families of the Euhypotrichina shown by six characters (1--6, described on left side in frames). Orthoamphisiellidae n. fam., Oxytrichidae Ehrenberg, 1838 and Parakahliellidae n. fam. are monophyletic groups and are separated by different morphogenetic anlagen developments in the two rightmost ventral cirral rows (characters 1--3). The Orthoamphisiellidae are separated from the other two families by generating a within anlage in each of the two rightmost ventral cirral rows (character 1, 2) thus, character 3 is not relevant for this family. The sister groups Oxytrichidae and Parakahliellidae are separated from each other by two different neokinetal anlagen developments (character 3) and by correlated presence/absence of the character 4 (character 4 refers to long primary primordia originating in posterior ventral half of cell's body, see Materials and Methods). Character 5 and 6 can be used to distinguish the families in interphase [19]. The outgroup to the investigated families is the family Holostichidae, that develops zigzag arranged midventral rows in three different ways [18] and renews some or all adoral membranelles of proter during division. Together they form the Euhypotrichina of which the outgroup is the Pseudohypotrichina formed mainly by the Aspidisca-Euplotes group [25]. Character states are according to Hennig [44].

Fig. 3. The three investigated families and species arranged as three monophyletic groups separated by five characters. The Orthoamphisiellidae n. fam. (4--12) develop the cirral rows by within anlagen. The two sister groups Oxytrichidae Ehrenberg, 1838 and Parakahliellidae n. fam. generate at least the two rightmost ventral cirral rows by neokinetal anlagen. The Oxytrichidae generate neokinetal 3 anlagen and long primary primordia (13--22, 39--42). The Parakahliellidae generate neokinetal 1 anlagen and long primary primordia are absent (23--38). DM indicates species of the two sister groups which develop dorsomarginal kineties (22--42). Numbers indicate the numbers of figures and are in order within their families as they have possibly evolved. Asterisks indicate species with ambiguous morphogenetic pattern, but they are more closely related to the Orthoamphisiellidae than to the Oxytrichidae and Parakahliellidae.

Definitions and terminology. Most of the terminology is according to [13a, 19, 48]. The neokinetal anlagen developments are described in [19] but can now be defined more precisely.

"Neokinetal 1" (N1) anlagen development designates the processes by which two small usually V-shaped anlagen-parts generate each at least two cirral rows for proter and opisthe's two rightmost ventral rows; the posterior anlagen-part for the opisthe develops from cirri of the second ventral cirral row from right; the anterior anlagen-part for the proter develops in four positions, viz. (1) also from cirri of the second ventral row from right (Fig. 24, 28, 29), (2) from cirri of the third ventral row from right (Fig. 26, 37), (3) from cirri of the rightmost ventral row (Fig. 27), but mostly (4) de novo, above the posterior anlagen-part (Fig. 25, 30--36, 38). For species belonging to the latter group some authors describe the two separate small V-shaped N1 anlagen-parts to be generated from one posterior cirrus only. They have observed a small field of basal bodies migrating or extending from the posterior V to the anterior V-shaped anlage [50, 67]. These developments are, however, included in the present paper in the group with N1 anlagen in which the anterior anlagen-part is considered to develop de novo [48].

"Neokinetal 3" (N3) anlagen development designates the process by which one large usually V-shaped anlage generates four cirral rows for proter and opisthe's two rightmost ventral rows. The anlage develops mainly from cirri of the second ventral cirral row from right by long primary primordia, which later splits horizontally (Fig. 14--22, 39--42).

"Neokinetal 5" (N5) anlagen development describes the process by which a new cirral row (usually a marginal row) is generated without or almost without using disaggregated cirri of the old row. The new row develops either right or left parallel to the old row and usually from anterior to posterior. In literature (except [19]), the N5 development is also named "within" anlage, despite the development outside of the old row.

"Long primary primordia" that originate from the posterior ventral part of the body from disaggregating cirri and/or from oral primordium are described in [28]. Such anlagen generate at least six cirral rows for proter and opisthe in the species with neokinetal 3 anlagen and is shown in detail for Paramphisiella caudata [23]. However, long primary primordia can be generated in a second and opposite way from disaggregating cirri in the anterior ventral half of body, i. e. in the frontal field right of the parental undulating membranes: long streaks are formed which later split horizontally and the posterior portions migrate posteriorly to a position right of opisthe's adoral membranelles. Such processes are described in the genus Orthoamphisiella, in Trachelochaeta gonostomoida and in Gonostomum affine (Hemberger, H. 1982. Revision der Ordnung Hypotrichida Stein, Ciliophora, Protozoa, an Hand von Protargolpräparaten und Morphogenesedarstellungen. Dissertation. The University of Bonn, Bonn, Germany; [22]). All long primary primordia are indicated in the computer drawings by solid lines that protrude from the posteriormost cirrus (Fig. 16 anlagen/rows 1--5).

The "split dorsal kinety" process is described in detail in [41]. The present paper shows that this development is part of a consistent dorsal pattern, i. e. three long dorsal kineties develop by within anlagen with at least one caudal cirrus at each posterior end. The left kinety, however, splits horizontally during development, placing its posterior half with the caudal cirrus (cirri) to the left. This pattern may not be confused with the multiple fragmentation of dorsal kineties which also originate from only three within anlagen (Fig. 25, 26, 31, 33). Recently, however, for Histriculus histrio a split dorsal kinety is described, but without caudal cirri [5].

The right marginal row (RM) usually is the rightmost cirral row between adoral zone of membranelles and dorsal/dorsomarginal kineties and contains equally spaced cirri of which none are enlarged. The rightmost ventral cirral row is the row left of the RM.

The term "highly evolved" mostly indicates an evolutionary state of species having a total number of only eight cirri in the two rightmost ventral cirral rows (i. e. usually 4 in each row) and having the position of the neokinetal anlagen development at the anteriormost cirrus of the second ventral row from right. Consequently, "lowly evolved" usually indicates more than eight cirri in the two rightmost rows and the position of the neokinetal anlage is below the anteriormost cirrus of the second row from right.

Diagnoses for the three monophyletic families Orthoamphisiellidae n. fam. and the sister groups Oxytrichidae Ehrenberg, 1838 and Parakahliellidae n. fam. and the genus Clara n. g. are given below. The three families and their assigned species are listed in Fig. 3 in order as they have possibly evolved. Definitions are given in Materials and Methods.
Orthoamphisiellidae n. fam. (Fig. 4--12). Diagnosis. The two rightmost ventral cirral rows develop each by one within anlage. Dorsomarginal kineties, split dorsal kineties and transverse cirri absent.

Type genus: Orthoamphisiella Eigner & Foissner, 1991 [20, 22].

This family is distinct from all other hypotrichs by developing all cirral rows by within anlagen development, except those anlagen developed by the oral primordium. The new cirral rows usually develop exactly within the old rows. In late stages of morphogenesis it is quite difficult to distinguish new from old cirri in protargol slides, since both are usually still perfectly in line. In the other groups old and new cirral row fragments can be observed lying side by side in late stages of morphogenesis. The sister groups Oxytrichidae and Parakahliellidae develop the two to three rightmost ventral rows by neokinetal anlagen, but all other cirral row anlagen usually also by within anlagen; these within anlagen in the sister groups, however, develop in fact slightly right or left of the old long cirral rows, as it is most distinct in neokinetal 5 (N5) anlagen developments. The development more or less outside of the old row was most likely the decisive evolutionary step resulting later in the neokinetal processes that produce four to five cirral rows each. Thus, the within development is considered as the earlier evolutionary process.
The Orthoamphisiellidae can be distinguished in interphase from the Oxytrichidae and the Parakahliellidae by absence of dorsomarginal kineties (in the Oxytrichidae and Parakahliellidae they are adjacent to the right marginal row and shorter than the other dorsal kineties, located usually in the anterior right half of the dorsal surface and they do not develop caudal cirri) and by absence of transverse cirri. The genus Orthoamphisiella was established without knowing its morphogenesis, thus it was assigned wrongly to the Amphisiellidae [20].
The existing family name Cladotrichidae is not used for the group developing only within anlagen (Orthoamphisiellidae), because in this very early description of morphogenesis of Cladotricha koltzowii some details are not or not clearly described which are now considered important (Fig. 5; [10]). For instance, a short row right of opisthe's first long row described in the original study may indicate a dorsomarginal kinety, as similarly described in the same study for C. variabilis and dorsal kineties are not described. The development of proter's anlage 2 and opisthe's anlage 3 is not described in detail either. C. koltzowii and C. variabilis belong to different phylogenetic lineages, the latter most likely to the Parakahliellidae, because it obviously develops a dorsomarginal kinety and groups and rows of cirri in the frontal and post-buccal area. C. halophila (Fig. 7; [70]), recently described, is possibly a junior synonym of Orthoamphisiella franzi (Fig. 6; [3]). Only caudal cirri , described for C. halophila, separate the two species; however, the last cirri of the left marginal row are described in O. franzi as easily mistaken for caudal cirri [3]. Parastrongylidium martini Fleury & Fryd-Versavel, 1984 [26] is closely related to P. oswaldi (Fig. 4; [1]), but obviously higher evolved, because it has fewer cirral rows and more enlarged frontal cirri. Pseudokahliella marina (Foissner, Adam & Foissner, 1982) Berger, Foissner & Adam, 1985 (Basionym: Kahliella franzi) [6, 36] is obviously also closely related to Parastrongylidium and thus belongs also to the Orthoamphisiellidae. Pseudokahliella marina is probably highest evolved in this group of three closely related species because of its evolved cirral pattern in the frontal field.

Fig. 4. Parastrongylidium oswaldi Aescht & Foissner, 1992 [1]. Supposed ancestor or early species of the Orthoamphisiellidae n. fam., indicated by (1) the within anlagen development in all cirral rows ; (2) the high number of long cirral rows; (3) many cirri mainly on dorsal side, which are composed only of one pair of basal bodies. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 5--6. Species of the Orthoamphisiellidae n. fam. 5. Cladotricha koltzowii Gajewskaja, 1926 [38]. Morphogenesis in [10]. The number of long cirral rows and the number of cirri in ventral rows 2--4 distinctly reduced. Cirri composed of only one basal body pair only in the left marginal row L1. Enlarged frontal cirri. 6. Orthoamphisiella franzi (Foissner, 1982) Eigner, 1995 (Basionyms: Gonostomum franzi, Kahliella franzi; [19, 27]). Morphogenesis in [3]. Number of long cirral rows reduced; the rightmost row 6 can be considered as right marginal row (RM). At least three enlarged frontal cirri. Three dorsal kineties built by pairs of basal bodies. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 7--8. Species of the Orthoamphisiellidae n. fam. 7. Cladotricha halophila Wilbert, 1995 [70]. No specific evolutionary changes and no specific morphogenetic and morphologic differences to Orthoamphisiella franzi, except for the presence of caudal cirri. 8. Trachelochaeta gonostomoida Hemberger, 1985 [42]. Morphogenesis in (Hemberger, 1982. Dissertation). One long rightmost ventral cirral row 6, but a high total number of eight ventral cirral anlagen 1--7, L1. Several enlarged frontal cirri. Three dorsal kineties with three caudal cirri. Origin of left (transverse) cirrus unknown. The morphogenetic pattern of forming long primary primordia in the frontal field is very similar to Orthoamphisiella stramenticola. General and symbol description given in Materials and Methods and Fig. 1.

Engelmanniella mobilis (Fig. 10; [27, 74]) is the only species outside the Parakahliellidae producing neokinetal waves and was therefore assigned in an earlier paper to the Kahliellidae [19]. Assignment is provisional because of distinct differences to the other orthoamphisiellid species, viz. old cirri in interphase, N5 anlagen development in both marginal rows and the unique development of a short dorsal kinety in the position where usually a dorsomarginal kinety develops. However, the two rightmost ventral rows develop by within anlagen, which shows E. mobilis more closely related to the Orthoamphisiellidae than to the groups which develop neokinetal anlagen for these two rows.

Fig. 9--10. Species of the Orthoamphisiellidae n. fam. 9. Orthoamphisiella stramenticola Eigner & Foissner, 1991 [20] and O. grelli Eigner & Foissner, 1993 [22]. One long rightmost ventral cirral row 5. About four enlarged frontal cirri. Only two dorsal kineties. Long primary primordia develop in the frontal field. The two species differ in the number of macronuclear nodules. 10. Engelmanniella mobilis (Engelmann, 1862) Foissner, 1982 (Basionym: Uroleptus mobilis; [24, 27]). Morphogenesis in [74]. One long rightmost ventral cirral row 4 and the total number of cirral anlagen reduced to six (including 1 and L1). Dorsal kineties reduced to one long and one short kinety. E. mobilis and Kahliella simplex are the only species outside the Parakahliellidae producing neokinetal waves [19]. General and symbol description given in Materials and Methods and Fig. 1.

Psilotricha succisa (Fig. 11; [29]). The only species developing a within and a neokinetal anlage in the rightmost ventral row 5. The neokinetal anlage in row 5 is possibly caused by the strange forming of the posterior part of row 4. P. succisa is considered more closely related to the Orthoamphisiellidae than to the Parakahliellidae because of the existence of anlagen in the rightmost ventral row 5, the three within anlagen in the two rightmost ventral rows and the lack of dorsomarginal kineties.

Circinella arenicola (Fig. 12; [33]). The decisive stages of morphogenesis, i. e. the position of the old rightmost ventral row 4 and its behavior while the new one is generated is not shown in the original drawings; it is possible that this row is generated by a process similar to the neokinetal 5 development. Opisthe's first three anlagen and a basal bodies field in such position generated by the oral primordium is also known from Paramphisiella caudata [23]. Furthermore, the possibly decisive development of the short dorsal kinety was not observed by the author in detail. It is described as probably having developed de novo as in Engelmanniella mobilis (Fig. 10). In this species, however, the short dorsal kinety develops in proter by within anlagen and only in opisthe in a unique way de novo; moreover, the short dorsal kinety in E. mobilis is positioned adjacent to the right marginal row as usual, but it is shown adjacent to the left marginal row in C. arenicola. This position is unique for a short dorsal kinety. Assignment is provisional, but the lack of neokinetal anlagen developments indicates that C. arenicola is more closely related to the Orthoamphisiellidae than to the other groups.

Fig. 11--12. Species of the Orthoamphisiellidae n. fam. 11. Psilotricha succisa (Müller, 1786) Foissner, 1983 [29, 52]. The rightmost ventral row 5 generates one within anlage and the posterior part of a N1 anlagen development. The second rightmost ventral row 4 is generated by a within anlage (proter) and the neokinetal anlage in row 5 (opisthe). Row 3 for opisthe is generated by the posterior cirri from row 4 as in Deviata abbrevescens (Fig. 13). Cirri of unknown origin are located between row 5 and 6. Two unique morphogenetic phenomena are reported, (1) proter's undulating membranes do not reorganize during division and (2) proter's leftmost (first) frontal cirrus develops in one anlage with the buccal cirri (row 1). Opisthe's anlagen for row 1 is generated by an early forking of streaks right of the oral primordium (Fig. 17, 20 in [29]). 12. Circinella arenicola Foissner, 1994 [33]. The rightmost ventral row 4 develops in an unique way. For opisthe it is entirely generated by the oral primordium, for proter from a basal bodies field, mainly originating from oral primordium. The old long ventral row 4 does not contribute to the forming of the new row 4, but is resorbed while the new row is generated. General and symbol description given in Materials and Methods and Fig. 1.

Oxytrichidae Ehrenberg, 1838 (Fig. 13--22, 39--42). Improved diagnosis. The two rightmost ventral cirral rows are generated by the neokinetal 3 (N3) anlagen development. One or more anlagen left of the two rightmost ventral cirral rows develop by long primary primordia that originate in the posterior part of the body. Dorsomarginal kineties present in highly evolved species with only 4 cirri in each of the two rightmost ventral rows. Transverse cirri usually present. Old (parental) cilia and cirri in interphase absent.
Many species presently assigned to the Amphisiellidae Jankowski, 1979 (including the type genus Amphisiella) are now considered to be lowly evolved Oxytrichidae, which makes the Amphisiellidae a junior synonym of the Oxytrichidae.
The Oxytrichidae are defined mainly by two distinct morphogenetic processes that are closely related to each other. The N3 anlage forms long primary primordia by definition. Long primary primordia originating from oral primordium are also formed in at least one anlage left of the N3 development. The sister group Parakahliellidae does not form such long primary primordia, neither in its N1 anlagen development nor in any other anlagen. Thus, the two sister groups can additionally be distinguished by their ability of forming anlagen by the process of long primary primordia.
Dorsomarginal kineties develop in the Oxytrichidae only in highly evolved species (except Kahliella simplex), i. e. in species that have only four cirri in each of the two rightmost ventral rows (Fig. 3 numbers 22, 39--42). Thus, Oxytrichidae and Parakahliellidae can be distinguished also in interphase by presence/absence of dorsomarginal kineties in species with more than four cirri in each of the two rightmost rows.
The definition of the "amphisiellid median cirral row" (ACR) used for defining the family Amphisiellidae in an earlier paper needs to be defined more precisely [23]. An ACR-like row develops more or less distinctly in most hypotrichs, mainly for two reasons. First, the anterior segment of the ACR, which is the anterior portion of the rightmost ventral row, is homologous to the "fronto-terminal cirri" (FTC) developing in most hypotrichs; the FTC can be defined as cirri of the rightmost ventral row that are positioned near the distal membranelles, i. e. if the rightmost row is long migration is not necessary; if it is short, the anterior portion of the rightmost row comes to its position by a more or less conspicuous migration (Fig. 19 row 6). Second, in most species the FTC are displaced to the left, seemingly upon the neighboring row, as if forming an ACR, but caused rather by anterior narrowing of the cell's body than by migration. Mainly for these two reasons Amphisiellides illuvialis (Fig. 29) and Gastrostyla steinii (Fig. 30) had previously been assigned to the Amphisiellidae [23]. Thus, processes forming an ACR are present in many Oxytrichidae and Parakahliellidae, most distinctly in the lowly evolved Oxytrichidae.
The forming of an ACR is most distinct in Pseudouroleptus caudatus and Hemiamphisiella terricola (Fig. 14, 15). In these two species the ACR is formed by cirri of three ventral rows. The posteriormost cirrus of the middle segment migrates to a postperistomial position. These postperistomial cirri were considered homologous to the postperistomial cirrus in Gastrostyla steinii (Fig. 30; [23]). There is, however, a significant difference in how this cirrus comes to a postperistomial position. In P. caudatus and H. terricola a specific migration occurs to displace this cirrus, whereas in G. steinii the anteriormost cirrus of row 4 is rather displaced to the right, probably by the enlargement of the oral apparatus during evolution. The cirral rows in an unknown early hypotrich were probably "straight" (Fig. 4). Later, by shortening of the body and by enlargement of the peristome, the cirri in the frontal field became displaced to the right. An effect of this is the difficulty to assign cirri in interphase to their proper rows and anlagen, which makes knowing the morphogenesis of most hypotrichs indispensable.
A peculiar morphogenetic character is the location of the development of the new right marginal row (RM) in three closely related oxytrichids. In these the new RM develops distinctly left of the old RM (Fig. 14--16); this may be significant regarding their evolution, because this group of three species and the following five (Fig. 17--21) do not develop dorsomarginal kineties (dorsomarginal kineties develop on right side of the RM). The latter five species develop the new RM more or less within the old RM. Parakahliellidae and highly evolved Oxytrichidae which generate dorsomarginal kineties develop the new RM also more or less within or distinctly right of the old RM (Fig. 22--42). Moreover, the evolutionary step from early within anlagen to the complex neokinetal anlagen was most likely initiated by the development of new cirral rows outside of the old row (see Orthoamphisiellidae). The decisive difference is probably that new cirri are not formed immediately from basal bodies of the old disaggregating cirri, but the new cirri are formed more or less independently, i. e. outside of the old rows. This evolutionary novelty separates the Oxytrichidae and Parakahliellidae from the Orthoamphisiellidae.

Fig. 13--14. Ancestor and species of the Oxytrichidae. 13. Deviata abbrevescens Eigner, 1995 [19]. Supposed ancestor of the Oxytrichidae, indicated by an incomplete early neokinetal 3 anlagen development in row 6 and long primary primordia indicated by the conspicuous processes in the cirral rows 4--6. Opisthe's anlage 3 develops from oral primordium and posterior cirri of the parental row 4. Proter's anlage 4 starts the streak development in the old row 4. This development deviates later to the old row 5 (anteriormost arrow). Opisthe's anlage 4 is generated within the old row 5. Proter's anlage 5 develops within the old row 6. Likewise within row 6 an anlage similar to a neokinetal 3 anlagen development generates the beginning of the anlagen development for opisthe's new row 5. Also generated within the old row 6 is the new row 6 for proter and opisthe (arrows connected to row 6). The developments in the posterior anlage of row 6 (i. e. the primitive neokinetal process for developing proter's anlage 6 and the deviating streak for opisthe's anlage 5) have great similarity to the N3 development for instance in Pseudouroleptus caudatus (Fig. 14). The anterior segment of the amphisiellid median cirral row (ACR) is indicated by the anterior six cirri of row 6 in D. abbrevescens, which is similar to the anterior segment of row 6 in P. caudatus. Both early oxytrichids have three long cirral rows on right ventral side extending to the posterior end of body. Therefore, the posteriormost cirri of these rows can be considered homologous to the transverse cirri of other oxytrichids. 14. Pseudouroleptus caudatus Hemberger, 1985 [42]. Morphogenesis in (Hemberger, 1982. Dissertation). All ventral cirral anlagen right of the adoral membranelles are generated by long primary primordia indicated in the computer drawing by the lines within the cirral rows protruding from the posteriormost cirrus (row 1--6). The short row 4 in proter is most probably developed de novo and placed in interphase between the anterior segment of the ACR (anterior segment of row 6) and row 5. The posteriormost cirrus of row 4 migrates to a postperistomial position and contributes to the forming of the oral primordium. Row 5 generates N3 with four streaks for proter and opisthe's new rows 5 and 6. No anlage in the rightmost cirral row (row 6) develops, as there is no anlage in the rightmost row in any oxytrichids and parakahliellids (except Paraurostyla weissei, Fig. 27). Thus, all cirri of row 6 are unused (inactive) and obviously resorbed in late dividers. The anlagen for the right marginal row 7 (RM) develop left of the old row and only about half of the cirri are used for generating the new RM. Typical split dorsal kinety pattern right of the RM. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 15--16. Species of the Oxytrichidae. 15. Hemiamphisiella terricola Foissner, 1988 [31]. Morphogenesis [23]. Morphogenetic processes are very similar to Pseudouroleptus caudatus (Fig. 14). Differences are in the ventral anlagen development in row 6, which has fewer cirri and some of them contribute to the neokinetal anlagen development and some migrate anteriorly. H. terricola is the first in a series that show such a migration in the rightmost ventral row (usually named fronto-terminal cirri or anterior segment of the amphisiellid cirral row). It is also the first in a series that reduces the number of cirri in the two rightmost ventral rows (here row 5 and 6) successively as they become higher evolved. 16. Paramphisiella caudata (Hemberger, 1985) Foissner, 1988 (Basionym: Uroleptoides caudata; [31, 42]). Morphogenesis in [23]. This species is similar to the former two species Pseudouroleptus caudatus and Hemiamphisiella terricola, however, without the peculiarities of their short row 4. Because P. caudata has the number of ventral anlagen reduced to five, the processes in the three closely related species possibly indicate an evolutionary strategy to reduce the number of ventral anlagen: the short row 4 of the former two species, which contributes in an unique way to the forming of the long median row, is now in P. caudata possibly incorporated in the developmental processes of the row 4. Thus, row 4 of P. caudata is possibly homologous to the rows 4 and 5 of the former two species. Anlagen 1--3 in P. caudata develop by long primary primordia, i. e. 1 and 2 by the oral primordium and contribution of frontal structures (undulating membranes and buccal cirrus, respectively), anlage 3 only by the oral primordium. Thus, no additional anlagen symbol is shown in row 3. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 17--18. Species of the Oxytrichidae. 17. Gonostomum strenua (Engelmann, 1862) [24]. Morphogenesis in [57]. The morphogenetic processes are not shown in detail in the original study, but they are similar to the processes in Paramphisiella caudata indicating long primary primordia for most ventral anlagen and a N3 anlagen development generating the two rightmost ventral rows 5 and 6. This N3 anlage most likely originates from posterior cirri of row 5 and the oral primordium. 18. Amphisiella australis Blatterer & Foissner, 1988 [7]. Morphogenesis in [65]. Like in Gonostomum strenua the number of cirri in the two rightmost ventral rows is distinctly reduced. In both, the short row 4 is in a similar position between row 5 and 6 as in Pseudouroleptus caudatus and Hemiamphisiella terricola (Fig. 14, 15) in which this row 4 forms the middle segment of the amphisiellid cirral row. In early dividers of A. australis a second field of basal bodies develops by disaggregating posterior cirri of row 5 that fuses with the oral primordium. Thus, the long primary primordia of the N3 anlagen development is generated by contribution of these two fields. Similar developments are reported from A. perisincirra, Paragastrostyla lanceolata and G. strenua. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 19--20. Species of the Oxytrichidae. 19. Amphisiella marioni Gourret & Roeser, 1888 [40]. Morphogenesis in [69]. The anterior segment of the row 6 is reduced to about five cirri and already similarly positioned as the homologous fronto-terminal cirri of the highly evolved Oxytrichidae; three of these cirri contribute to the forming of the neokinetal anlage. Six dorsal kineties are reported to develop by within anlagen. This is unique within the described four families which have only a maximum of three within anlagen for the dorsal kineties. Possibly some dorsal kineties are generated by multiple fragmentation. A. marioni develops transverse cirri from anlage 2 and 3, which is also unique for lowly evolved oxytrichids. 20. Amphisiella perisincirra (Hemberger, 1985) Eigner & Foissner, 1994 (Basionym: Tachysoma perisincirra; [23, 42]. Morphogenesis in [4]. This species already shows one character of the highly evolved oxytrichids, i. e. the number of cirri in the rightmost row 6 is reduced to four. However, it still has more than four cirri in the second ventral row 5 from right and the N3 development does not yet develop at the anteriormost cirrus of this row. In another description of morphogenesis of A. perisincirra (Hemberger, 1982. Dissertation) the row 5 even shows six cirri. Similar morphogenetic developments see A. australis (Fig. 18). General and symbol description given in Materials and Methods and Fig. 1.

Fig. 21. Paragastrostyla lanceolata Hemberger, 1985 [42]. Morphogenesis in (Hemberger, 1982. Dissertation). Unique cirral pattern. The anlagen 1--5 possibly develop by long primary primordia. The rightmost ventral row 7 consists of three fronto-terminal cirri only. Oxytrichids usually possess in the rightmost row four cirri, however only two in the anterior position. In contrast to the other oxytrichids, no transverse cirri are described. General and symbol description given in Materials and Methods and Fig. 1.

Kahliella simplex (Fig. 22; [19]). A reinvestigation of the original protargol slides shows without a doubt one large V in very early dividers generated by cirri of the second ventral row 6 from right. This large V later splits horizontally as it is typical for a N3 development. Dorsomarginal kineties put K. simplex in the evolutionary line near the group of four highly evolved Oxytrichidae (Fig. 3 numbers 39--42); the long cirral rows, however, put it approximately between Pseudouroleptus caudatus and Hemiamphisiella terricola (Fig. 14, 15). K. simplex and Engelmanniella mobilis (Fig. 10) are the only species outside the Parakahliellidae developing neokinetal waves [19]. Moreover, K. simplex is the only species in the oxytrichid lineage that does not develop long primary primordia left of the two rightmost ventral rows 6 and 7. Similarly unusual is Amphisiellides illuvialis (Fig. 29), which also shows great variability in number and length of the right ventral cirral rows [23].

Fig. 22. Kahliella simplex (Horváth, 1934) Corliss, 1960 [11, 46]. Morphogenesis in [19]. Two neokinetal waves develop, which is not typical for oxytrichids. One to the right originating from row 7 and one to the left originating from the left marginal row L1. K. simplex is the only lowly evolved oxytrichid species developing a dorsomarginal kinety. One kinety on dorsal side is a "combined cirral row" (L2; [19]). General and symbol description given in Materials and Methods and Fig. 1.

Parakahliellidae n. fam. (Fig. 23--38). Diagnosis. The two rightmost ventral cirral rows for proter and opisthe are generated by the neokinetal 1 (N1) anlagen development. Dorsomarginal kineties present. Transverse cirri usually present. Old (parental) cilia and cirri may be present in interphase.

Type genus: Parakahliella Berger, Foissner & Adam, 1985 [6].
Many species that are presently assigned to the Kahliellidae Tuffrau, 1979 are assigned to the Parakahliellidae in the present paper (Fig. 23--38). The genus Kahliella is the type of Tuffrau's family Kahliellidae [61, 62], but is assigned now to the Oxytrichidae (see above), which makes the Kahliellidae a junior synonym of the Oxytrichidae [61]). The name Parakahliellidae still includes Tuffrau's decision to honor the great self-taught ciliatologist Kahl and gives some continuity in the family name.
The definition of the family Kahliellidae in an earlier paper is being updated for the Parakahliellidae by the results given in the present paper [19]. Thus, the two sister groups Oxytrichidae and Parakahliellidae can now be separated by whether they develop neokinetal 3 or neokinetal 1 anlagen or not and their correlated characters. The seemingly independent two anlagen-parts of the neokinetal 1 anlagen development are recognized as belonging to one common and complex anlagen development. In contrast, in the neokinetal 3 anlagen these two anlagen-parts are united in one anlage.

Fig. 23. Neogeneia hortualis Eigner, 1995 [19]. Supposed ancestor of the Parakahliellidae indicated by (1) neokinetal 1 anlagen development still in the rightmost row 8 (N1 anlagen develop usually two places left in the second ventral cirral row from right), (2) dorsomarginal kineties still without displacement to the dorsal side and (3) neokinetal waves (old cirral row fragments). The development of the dorsomarginal kinety is indicated by the short row of ciliary pairs forming the anterior portion of the rightmost row 8. The old (parental) cirri between row 5 and 6 are passed on by the process of neokinetal wave originating here in an unique way from row 8 (the usual neokinetal wave would originate here from row 6). This special way of neokinetal wave is possibly responsible for placing later the N1 development from a rightmost position (N. hortualis) to the usual position in the second rightmost ventral row (see Parakahliella macrostoma, Fig. 24 row 5). The left marginal rows L1--L4 develop by "neokinetal 2" (N2) development described in detail in [19]. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 24. Parakahliella macrostoma (Foissner, 1982) Berger, Foissner & Adam, 1985 (Basionym: Paraurostyla macrostoma [6, 27]). Similar developments as in Neogeneia hortualis (Fig. 23): N1 still develops in the rightmost row 7. The dorsomarginal kinety already migrates to the right and to the dorsal side, respectively and survives one generation as an old ciliary row like in some other parakahliellids. The additional row 7 in N. hortualis is not present any more and the rows 6 in both species are most likely homologous. Both rows 6 produce according to the neokinetal wave the old cirri to their left. Row 5 in P. macrostoma generates additionally a N1 development already at the usual position, i. e. in the second ventral cirral row from right (if considering the row 7 as RM). The left marginal row L1 generates a third N1 development. Variability of cirral pattern in P. macrostoma is great, thus only the basic morphogenetic events are shown in the computer drawing. General and symbol description given in Materials and Methods and Fig. 1.

Onychodromus quadricornutus (Fig. 25; [37]). The anlagen development shown here is not certain, because the original description and drawings are ambiguous concerning the two rightmost ventral anlagen, which are described only as splitting. The drawings are unclear with respect to which streak is generated by which anlage and row; the length of row 12, which is important for understanding the anlagen developments, is distinctly different in two drawings, indicating different morphogenetic patterns (Fig. 8, 15 in [37]). However, the most likely developments are shown in the computer drawing.

Amphisiellides illuvialis (Fig. 29) and Gastrostyla steinii (Fig. 30). Former assignment see Oxytrichidae.

Fig. 25. Onychodromus quadricornutus Foissner, Schlegel & Prescott, 1987 [37].The only parakahliellid species in which obviously both anlagen-parts of N1 develop in the third ventral row from right (row 11). The anterior N1 anlagen-part develops de novo and generates proter's rows 11--13, the posterior N1 anlage-part develops from cirri of the old row 11 and generates opisthe's new rows 11--13. The two to three rightmost ventral rows are reported to generate no anlagen or streaks. Proter and opisthe's right marginal row 14 (RM) and opisthe's left marginal row L1 develop by typical neokinetal 5 (N5) anlagen development, i. e. all or nearly all cirri of these three old rows are intact (unused) while the new cirri develop. Therefore, in late stages of morphogenesis these old and new rows can be observed lying side by side; surprisingly, no old cirri in interphase are reported for this species. The many dorsal kineties develop by only three within anlagen for each proter and opisthe. Like in most evolved parakahliellids, two dorsomarginal kineties develop. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 26. Kerona polyporum Ehrenberg, 1835 [16]. Morphogenesis in [43]. The N1 anlage for proter is not generated in the same row as for opisthe (i. e. in the second rightmost ventral row), but in the third ventral row from right and generates the three rightmost ventral rows 4, 5 and 6 as in Onychodromus quadricornutus (Fig. 25). Opisthe's anlagen for these rows develop as usual. Number of anlagen in frontal field reduced to three; anlagen 1 and 2 for proter are generated most likely de novo. The left marginal row (L1) is generated by neokinetal 5 development like in most parakahliellids; in this species all cirri of the old row are unused. Two dorsomarginal kineties and many dorsal kineties develop, the latter however, only from three anlagen each for proter and opisthe as in O. quadricornutus. The authors of morphogenesis describe opisthe's anlagen 3 and 4 generated by posterior cirri of row 4; however their Fig. 1e shows these anlagen more likely generated by the oral primordium. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 27. Paraurostyla weissei (Stein, 1859) Borror, 1972 [8, 58]. Morphogenesis in [48, 71]. The only species in the four investigated families that generates an anlage (the anterior anlagen-part of N1) in the rightmost ventral cirral row 9. This row develops as usual side by side with the second rightmost ventral row 8. Most cirri of row 9 migrate as fronto-terminal cirri or to use its synonym, as the anterior segment of the amphisiellid cirral row (ACR) anteriorly and are positioned upon the row 8. This gives in interphase the impression of one nearly body long cirral row, as it develops in some lowly evolved oxytrichids (Fig. 15, 16). The dorsal kinety that is adjacent to the left marginal row also develops in an unusual way: the anlagen develop their streaks not within, but right of the old kinety (D1). Two within anlagen develop probably in individuals with a longer row 7, instead of one within and one de novo anlage. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 28. Parentocirrus hortualis Voss, 1997 [66]. This species shows two ways of N1 anlagen development. The usual way for rows 4--6 is shown in the left computer graphic. The seldom occurring way similar to developments in Kerona polyporum (Fig. 26) is shown in the frame. Different from K. polyporum is the development of proter's row 5, which is in P. hortualis generated by an anlage within the old row 5 and in K. polyporum by the N1 anlage in row 4. In same rare specimens of P. hortualis the unused row 6 is not resorbed during cytokinesis, but is passed on to the next generation (old row between row 6 and 7). General and symbol description given in Materials and Methods and Fig. 1.

Fig. 29--30. Species of the Parakahliellidae n. fam. 29. Amphisiellides illuvialis Eigner & Foissner, 1994 [23]. Most likely cirri from row 5 contribute to the forming of the N1 development for proter. Row 4 shows a great variability in number of cirri, thus the N1 anlagen-part for proter may also develop de novo. 30. Gastrostyla steinii Engelmann, 1862 [24]. Morphogenesis in (Hemberger, 1982. Dissertation). The anterior N1 anlagen-part is generated de novo, above the row 5. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 31. Onychodromus grandis Stein, 1859 [58]. Morphogenesis in [60]. Both N1 anlagen-parts generate three cirral rows each for proter and opisthe, thus, cirri of row 4 are unused like those of row 6. Several dorsal kineties are generated by only three within anlagen. General and symbol description given in Materials and Methods and Fig. 1.

Coniculostomum monilata (Fig. 32; [50]). This species shows several rows of old cirri on ventral and old cilia on dorsal sides, products of neokinetal waves, which is typical for parakahliellids. The original drawing (Fig. 1 in [50]) shows four cirri in each of the two rightmost rows 5 and 6. However, table 1 of the original study describes eight to ten frontal cirri and five to six transverse cirri, which possibly makes two more cirri in row 6 and one more in row 6 or 5 (Fig. 32). Moreover, the original Fig. 9 shows in proter's future row 5 five well developed cirri. The authors describe in their table 2 that the anlagen for row 5 and 6 are generated by common (long) primary primordia, observed in their slides, although they did not draw out this stage. Their Fig. 5 and 6, however, show two typically separated small V-shaped N1 anlagen-parts for proter and opisthe (see Materials and Methods). The origin of anlage 2 is described in a similar way. According to the detailed drawings the pattern, as it is most likely to be, is shown in the computer drawing of the present paper.

Fig. 32. Coniculostomum monilata (Dragesco & Njiné, 1971) Njiné, 1979 [19] (Basionym: Laurentia monilata [14, 54]). Morphogenesis in [50]. The N1 anlage generates also the row 4, obviously by participation of the first and second cirrus of the old row 4. There are several rows of old cirri on ventral and old cilia on dorsal side, which are products of neokinetal waves [19]. Usually four cirri develop in each of the two rightmost ventral rows. General and symbol description given in Materials and Methods and Fig. 1.

Pattersoniella vitiphila (Fig. 33; [30]). Most probably the left ventral field evolved independently from evolutionary changes in the right ventral field. P. vitiphila, as Coniculostomum monilata, links lowly and highly evolved parakahliellids; both species usually generate only four cirri in each of the two rightmost ventral rows. The posterior N1 anlagen-part is generated by the anteriormost cirrus of the second ventral row from right as typical in highly evolved species. The total number of ventral anlagen is high in P. vitiphila and old ciliary rows exist on the dorsal side, whose origin are not reported in detail. The dorsal kineties adjacent to the dorsomarginal kineties are described as being developed by multiple fragmentation. This also shows the evolutionary status of P. vitiphila between lowly and highly evolved parakahliellids, because the dorsal pattern represents most likely early developments, which lead to the typical split dorsal kinety pattern (see Materials and Methods).

Fig. 33. Pattersoniella vitiphila Foissner, 1987 [30]. Anlagen/cirral rows 1--3 and 8--10 form the pattern traditionally referred to as the typical oxytrichid pattern. Dorsal kineties are in an intermediate evolutionary stage, which later results most likely in the typical split dorsal kinety pattern. General and symbol description given in Materials and Methods and Fig. 1.

Histriculus muscorum (Fig. 34; [6]). The authors give only drawings, no detailed description of morphogenesis. They refer to the descriptions of Oxytricha granulifera (Fig. 41) and Clara vorax + C. pustulata (Fig. 37). Both, however, develop a basically different morphogenetic pattern. The original drawings are ambiguous, i. e. the rightmost anlagen are shown rather according to N1 developments; nevertheless, there are also basal bodies crossing the fibers of the cytopharynx as if indicating long primary primordia. Nieto & al. give a description and photographs of divisional morphogenesis of a very similar species, both not showing long primary primordia, but clearly indicating the typical two small V-shaped patterns of the N1 development [53]. H. muscorum has been renamed to Sterkiella histriomuscorum (see Comparison with recent studies).
Steinia sphagnicola (Fig. 35; [67]). The authors describe the caudal cirrus produced by the split dorsal kinety in another position; the position shown in the computer drawing, however, is more probable and also in accordance with Fig. 47 in [67].

Fig. 34. Histriculus muscorum (Kahl, 1932) [49]. Morphogenesis in [6] (renamed to Sterkiella histriomuscorum [5]). Typical highly evolved parakahliellid species (N1), developing four cirri in each of the two rightmost ventral rows 5 and 6, and the posterior N1 anlagen-part develops at the anteriormost cirrus of the second rightmost row 5. Row 6 is the neokinetally developed rightmost ventral row, of which two cirri migrate during division to a position near the distal membranelles. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 35. Steinia sphagnicola Foissner, 1989 [32]. Morphogenesis in [67]. Like Histriculus muscorum (Fig. 34), typical highly evolved morphogenetic pattern with neokinetal 1 anlagen development. The species differs in its morphology from other similar oxytrichids mainly by the shape of the undulating membranes [32, 67]. General and symbol description given in Materials and Methods and Fig. 1.

Cyrtohymena muscorum (Fig. 36; [63]). The original drawings of morphogenesis are ambiguous. The cirral anlagen develop separately, despite their seemingly long primary primordia; it is probable that some early dividers are in fact reorganizers. However, the author agrees with the developments shown in the computer drawing of the present paper (Voss, H. J., pers. commun.). The new rows 5 and 6 for proter are possibly not generated de novo, but generated as in Clara pustulata (Fig. 37).

Urosomoida agiliformis (Fig. 38; [35]). In another description of morphogenesis the anlagen develop according to the N3 development [39].

Fig. 36. Cyrtohymena muscorum (Kahl, 1932) Foissner, 1989 (Basionym: Steinia muscorum [32, 49]), left original drawing. Morphogenesis in [63]. Notohymena rubescens Blatterer & Foissner, 1988 [7], right original drawing. Morphogenesis in [64]. Both species develop nearly the same morphology and the same morphogenetic pattern; both species are separated by a different shape of the undulating membranes. General and symbol description given in Materials and Methods and Fig. 1.

Clara n. g. Diagnosis. Highly evolved Parakahliellidae with four cirri in each of the two rightmost ventral rows. During divisional morphogenesis the anterior N1 anlagen-part develops at the anteriormost cirrus of row 4 and generates proter's rows 4--6. Old (parental) cirri and cilia in interphase absent [72].

Stylonychia mytilus (Müller, 1773) Ehrenberg, 1830 and S. lemnae Ammermann & Schlegel, 1983 belong to the same genus [73] and belong to the monophyletic group that develops neokinetal 3 anlagen and long primary primordia (Oxytrichidae) as shown in the present paper (Fig. 39). S. pustulata (Müller, 1786) Ehrenberg, 1835 and S. vorax Stokes, 1885 also belong to one genus [72], but to the group developing neokinetal 1 anlagen and separate primary primordia (Parakahliellidae; Fig. 37). Thus, morphogenetic data and molecular data suggest that the genus Stylonychia is not monophyletic [55]. Therefore, a new genus is erected for the latter two species, Clara n. g., with species Clara pustulata (Müller, 1786) nov. comb. (here designated as type of the genus) and C. vorax (Stokes, 1885) nov. comb. Clara was the youngest daughter of Christian Gottfried Ehrenberg and in his old age she was a great help to her father in his scientific work [13 b]; thus it is a pleasure to name the new genus in her memory. Morphology and morphogenesis of the new genus Clara is described in detail in [72].

Fig. 37. Clara vorax (Stokes, 1885) n. comb. (Basionym: Stylonychia vorax) and C. pustulata (Müller, 1786) n. comb. (Basionyms: Kerona pustulata, Stylonychia pustulata) [52, 59]. Morphogenesis in [72]. The anterior N1 anlagen-part develops at the anteriormost cirrus of row 4 and generates proter's rows 4--6. Only the very early stages of morphogenesis, i. e. the forming of the oral primordium is different in the two species. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 38. Urosomoida agiliformis Foissner, 1982 [27]. Morphogenesis in [35]. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 39. Stylonychia mytilus (Müller, 1773) Ehrenberg, 1830 [15, 51] and S. lemnae Ammermann & Schlegel, 1983 [2]. Morphogenesis in [73]. First of four highly evolved species (Fig. 39--42) developing neokinetal 3 anlagen and long primary primordia in the left frontal field according to the definition of the Oxytrichidae. These four highly evolved oxytrichid species develop dorsomarginal kineties in contrast to most of the lowly evolved Oxytrichidae. This group of four species develops similar morphogenetic patterns, differing mainly in the development of row 4. Opisthe's anlage 4 in S. mytilus and S. lemnae is generated by the N3 anlage, whereas proter's anlage 4 is generated by a within anlage in row 4. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 40. Oxytricha gigantea Horváth, 1933 [45]. Morphogenesis in [3]. Row 4 develops by long primary primordia, i. e. one long streak extends from opisthe to the parental frontal field and the second cirrus of row 4 disaggregates and contributes to this streak. Later also the anteriormost cirrus of row 4 disaggregates and probably also contributes to the forming of this streak. General and symbol description given in Materials and Methods and Fig. 1.

Fig. 41--42. Species of the Oxytrichidae. 41. Oxytricha granulifera Foissner & Adam, 1983 [34]. Proter's row 4 develops by a within anlage and opisthe's row 4 by the oral primordium. 42. Urosoma macrostyla (Wrzesniowski, 1870) [75]. Morphogenesis in [28]. The new rows 4 develop for proter and opisthe by one within anlage each in the old row 4. General and symbol description given in Materials and Methods and Fig. 1.

Evolution of morphogenetic processes. The monophyletic groups suggested in the present paper are based on three morphogenetic processes, viz. within anlagen, neokinetal anlagen and long primary primordia (Fig. 2 character 2--4). Within anlagen are considered the earliest evolved morphogenetic process, because they develop at least in some cirral rows in all investigated groups. Evolutionary changes to neokinetal and long primary primordia anlagen were most likely initiated by generating new cirral rows outside of the old rows (see Orthoamphisiellidae) and by shortening of cirral rows. The processes possibly evolved in three steps, viz. (1) within anlagen and long primary primordia originating in the frontal field, (2) neokinetal 3 anlagen and long primary primordia originating from the posterior ventral field, (3) neokinetal 1 anlagen. The N1 development evolved probably by horizontal splitting of N3 anlagen resulting in two N1 anlagen-parts. This is most likely also shown by the development of streaks which still connect in very early dividers the places where later the two separate N1 anlagen-parts are generated [50, 67]. The evolutionary changes within the monophyletic groups (Fig. 3) from species to species can be followed in the Fig. 4--42.
Dorsal kineties develop rather uniformly, most likely because of less selection pressure on this side of the body, i. e. not more than three within anlagen develop; and in many species they form the split dorsal kinety pattern. The multiple fragmentation of dorsal kineties shown in four species is probably an intermediate evolutionary stage leading to the split dorsal kinety pattern (see Materials and Methods).
The shape of the adoral zone of membranelles and the undulating membranes, the number of pretransverse and caudal cirri, the flexibility, size and shape of the body, special cortical granules and similar characters can be used only on a low taxonomic level. Large groups can be recognized by using protargol staining and research into morphogenesis. "Tracing out the dynamics of the pattern during ontogeny can provide data potentially of great significance in determination of the organism's phylogenetic affinities" [12].

Comparison with two recent studies. A classification of the class Hypotrichea using morphogenetic, ultrastructural, ecophysiological and life cycle data to define the subclasses Euplotia and Oxytrichia was recently established [62]. The Euplotia contain genera used in the present paper's Fig. 2 as the outgroup Pseudohypotrichina. The Oxytrichia contain three Orders of which the Urostylida contain genera which are used in Fig. 2 as the outgroup Holostichidae. Another order of the subclass Oxytrichia is the order Oxytrichida containing the families Kahliellidae, Amphisiellidae and Oxytrichidae. However, the genus Orthoamphisiella, the type of the new family Orthoamphisiellidae, which is suggested in the present paper, is not mentioned [20, 22]. Similarly, many decisive studies that have been published recently are considered only in the present paper [1, 19, 23, 30, 34, 35, 60, 63--67, 71, 72]. Moreover, morphogenetic patterns are used only in a general way, whereas the present paper is based on such morphogenetic data and each species is morphogenetically defined by a computer drawing. Thus, the assignments of taxa to the families in the present paper is quite different. For instance, genera which are assigned in [62] to the Kahliellidae are assigned in the present paper to the Orthoamphisiellidae, because of fundamental differences in anlagen formation.

Another recent study gives a characterization of the Oxytrichidae, using 18 characteristically arranged ventral cirri and cirral groups and the fragmentation of at least one dorsal kinety [5]. However, the ventral pattern depicted in [5] is distinctly different from some of the taxa assigned to the Oxytrichidae (cf. Fig. 17, 34, 38, 42, see Coniculostomum monilata above). Pattersoniella vitiphila also develops in its anlagen 1--3 and 8--10 such cirral groups, thus also species with several more ventral anlagen can develop one such typical pattern (Fig. 33). As shown in the present paper, this pattern derives from two phylogenetic lineages and its evolution can be followed in the computer drawings of the two sister groups Oxytrichidae and Parakahliellidae. Furthermore, several genera assigned to the Oxytrichidae by these researchers do not develop fragmented (split) dorsal kineties, which is the second character they use; meanwhile several genera which do develop such dorsal kineties are not included. Moreover, Pseudouroleptus caudatus (Fig. 14), which they do not mention, is a lowly evolved species that also develops such a split dorsal kinety and therefore this character cannot be used to characterize the most highly evolved hypotrich group. Furthermore, they use the participation/no participation during anlagen development of the second cirrus of the second ventral row from right for dividing the Oxytrichidae into two groups. This character, however, cannot be decisive to divide such a large group, because the first cirrus of this row generates an anlage (N1 or N3) in all highly evolved Oxytrichidae; the participation of that second cirrus depends as usual only on the distance to the (next) first cirrus: if the second cirrus is near the first cirrus, it participates (Fig. 36, 38 first and second cirrus of row 5); if it is away from the first cirrus and rather near to the transverse cirri, it usually does not participate in anlagen formation (Fig. 35, 37). Only in one small group, which these authors name Gonostomum-Urosoma-Tachysoma lineage, they recognize the decisive character of long primary primordia used in the present paper. This character is recognized by them only if all fronto-ventral-transverse cirri are generated by long primary primordia. They recognize, however, that the origin of the two rightmost ventral rows is of great cladistic significance. Morphogenetic processes are considered in that study only from the traditional and highly evolved Oxytrichidae and therefore they cannot recognize the processes that separate the other species of the two sister groups. These processes are, however, the same as those separating the Oxytrichidae into two groups. A description by (Hemberger, 1982. Dissertation) is used in [5] for comparing Gonostomum; in the present paper the description by Song (Fig. 17) is used for this genus. Both descriptions show the same decisive morphogenetic processes used in the present paper for separating the two monophyletic sister groups Oxytrichidae and Parakahliellidae, but distinct differences occur in the way the long primary primordia are generated (see Materials and Methods). They assign 14 morphogenetically investigated taxa to two oxytrichid groups of which 11 are also analyzed in the present paper. They describe Histriculus histrio, but nearly all early stages of morphogenesis are missing. This description can therefore not be used for morphogenetic comparison. Sterkiella histriomuscorum is Histriculus muscorum of the present paper and of the original description of morphogenesis [6]. The three morphogenetically investigated taxa used in [5] and not used in the present paper are Tachysoma, because the author (Hemberger, 1982. Dissertation) could not clear up the origin of the decisive right ventral cirral rows, Histriculus histrio, which is not used for reasons given above, and Onychodromopsis, which has not been published as of yet.

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