Zosterodasys Deroux 1978

Zosterodasys Deroux, 1978

(Fig. 1)

Zosterodasys Deroux, 1978: 464; Fernandez-Leborans & Alekperov 1996: 3 (taxonomic revision of the genus); Kivimaki et al. 1997: 226 (ultrastructural anatomy); Aescht 2001: 177 (catalogue of generic names of ciliates); Lynn & Small 2002: 548 (illustrated guide to genera); Jankowski 2007: 729 (brief generic review and list of species); Lynn 2008: 397 (list of genera); Gong et al. 2009: 339 (phylogenetic position of the genus); Kivimaki et al. 2009: 323 (phylogenetic position of the genus).

Diagnosis. Orthodonellidae with obovoidal to ellipsoidal body not differentiated into an anterior rostrum. Macronucleus globular to narrowly ellipsoidal, rarely lenticular or bowknot-shaped; usually a single rarely up to three micronuclei. Typically several contractile vacuoles, posterior one sometimes enlarged. Synhymenium composed of narrowly spaced dikinetids extending obliquely from left to right dorsal surface across ventral side and thus interrupting all ventral ciliary rows and some dorsal ones. Cyrtos composed of a central cytopharyngeal tube lined by postciliary microtubules and nematodesmal rods arranged around cytostome in a ring.

Type species. Zosterodasys agamalievi Deroux, 1978 by original designation and monotypy [Articles 68.2 and 68.3 of the ICZN (1999)].

Etymology. Not given in the original description. Composite of the Greek noun zóstér (ζωστήρ [m]; girdle), the thematic vowel · o-, and the Greek adjective das ỹ s (δασὺς [m]; dense), meaning “the dense girdle” and obviously referring to the synhymenium composed of densely arranged cilia encircling the body as a girdle. Masculine gender according to the Article 30.1.2 of the ICZN (1999).

Comparison with related genera. Within the order Synhymeniida, Zosterodasys most resembles Orthodonella and Chilodontopsis. However, Orthodonella is distinguished by the anterior body portion which is differentiated into a rostrum bent to the left (vs. no such rostrum in Zosterodasys). Chilodontopsis differs from Zosterodasys only by some details of the synhymenium. According to Deroux (1978) the synhymenium extends obliquely from the left dorsal surface across the ventral side but terminates one or two ventral ciliary rows past the oral opening in Chilodontopsis, while it extends obliquely from the left to the right dorsal surface across the ventral side and thus interrupting all ventral ciliary rows in Zosterodasys. According to Lynn & Small (2002) and Lynn (2008) the synhymenium of Chilodontopsis is, in addition, sparsely ciliated, i.e., composed of loosely arranged basal bodies, while that of Zosterodasys is thickly ciliated, i.e., composed of narrowly arranged basal bodies.

Remarks. Altogether 31 species were originally described or subsequently combined with Zosterodasys (Alekperov 1984; Aliev 1990; Deroux 1978; Fernandez-Leborans 1990; Fernandez-Leborans & Alekperov 1996; Foissner et al. 1994; Gong et al. 2007; Jankowski 2007; Petz et al. 1995). However, we recognize only nine of them as valid Zosterodasys species, 11 represent nomenclatural synonyms, one is a junior primary homonym, five are classified as species inquirendae, and five belong to other genera (Table 2). All species recognized here as reliable exactly meet the definition of Zosterodasys in Deroux (1978).