[ref. ID; 7423 (Eigner, 1997)]
Orthoamphisiellidae n. fam.
The two rightmost ventral cirral rows develop each by one within anlage. Dorsomarginal kineties, split dorsal kineties and transverse cirri absent.
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 (Eigner and Foissner, 1991)
Orthoamphisiella Eigner & Foissner, 1991
Oxytrichidae Ehrengerg, 1838
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 four 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 distict 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 analage 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 an additionaly be distinguished by their ability of forming anlagen by the process of long primary primordia.
Dorsomarginal kinety 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. 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 (Eigner & Foissner 1994). An ACR-like row develop 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. 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 and Gastrosytla steinii had previously been assigned to the Amphisiellidae (Eigner and Foissner 1994). Thus, processes forming an ACR are present in many Oxytrichidae and Parakahliellidae, most distinctly in the lowly evolved Oxytrichidae.
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 distintly left of the old RM; this may be significant regarding their evolution, because this group of three species (Pseudouroleptus caudatus, Hemiamphisiella terricola, Paramphisiella caudata) and the following five (Gonostomum strenua, Amphisiella australis, Amphisiella marioni, Amphisiella perisincirra, Paragastrostyla lanceolata) 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 old RM. Parakahiliellidae and highly evolved Oxytrichidae which generate dorsomarginal kineties develop the new RM also more or less within or distinctly right of the old RM. 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. 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.
Parakahliellidae n. fam.
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.
Many species that are presently assigned to the Kahliellidae Tuffrau, 1979 are assinged to the Parakahliellidae in the present paper. The genus Kahliella is the type of Tuffrau's family Kahliellidae (Tuffrau 1979; Tuffrau and Fleury 1994), but is assigned now to the Oxytrichidae, which makes the Kahliellidae a junior synonym of the Oxytrichidae. 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 (Eigner 1995). 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 seemingy 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.
Parakahliella Berger, Foissner & Adam, 1985
Definition and terminology
Neokinetal 1 (N1)
Neokinetal 1 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, (2) from cirri of the third ventral row from right, (3) from cirri of the rightmost ventral row, but mostly (4) de novo, above the posterior anlagen-part. 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 (Kamra and Sapra 1990; Voss and Foissner 1996). 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 (Jerka-Dziadosz and Frankel 1969).
Neokinetal 3 (N3)
Neokinetal 3 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.
Neokinetal 5 (N5)
Neokinetal 5 anlagen development described the process by which a new cirral row (usually a marginal rows) 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 Eigner 1995), the N5 development is also named "within" anlage, despite the development outside of the old row.
"Long primary primordia"
Long primary primordia that originate from the posterior ventral part of the body from disaggregating cirri and/or from oral primordium are described in (Foissner 1983). Such anlagen generate at least six cirral rows for proter and opisthe in the species with neokinetal 3 anlagen and shown in detail for Paramphisiella caudata (Eigner and Fossiner 1994). 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 with 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 1982; Eigner and Foissner 1993).
"Split dorsal kinety"
The "split dorsal kinety" process is described in detail in (Grimes and Adler 1976). The present paper shows that this development is part of a consitent 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 be confused with the multile fragmentation of dorsal kineties which also originate from only three within anlagen. Recently, however, for Histiculus histrio a split dorsal kinety is described, but without caudal cirri (Berger and Foissner 1997).
"Right marginal row (RM)"
The right marginal row (RM) usually is the rightmost cirral row between adoral zone of membranelles and dorsal/dorso marginal 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 four in each row) and having the position of the neokinetal anlagen development at the anteriormost cirrus of the second ventral row from right. "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.