Timoshkin, O. A.; Zaytseva, E. P.; Gutsol, M. V. (2009). New species of microscopic psammophilous turbellarians of the genus Opisthocystis (Plathelminthes, Kalyptorhynchia) from Lake Baikal. Zoologicheski Zhurnal, 88 (4): 398-413

237547

Timoshkin, O. A.; Zaytseva, E. P.; Gutsol, M. V.

2009

88 (4): 398-413

Publication

Available for editors  

Illustrated descriptions of 8 new species of the genus Opisthocystis Sekera 1911 inhabiting the sandy bottom of the Lake Baikal littoral zone mostly at depths of less than 10m are given: Opisthocystis novitzkyi Timoshkin, Zaytseva et Gutsol sp. n.; Opisthocystis meyeri Timoshkin, Zaytseva et Gutsol sp. n.; Opisthocystis marinae Timoshkin, Gutsol et Zaytseva sp. n.; Opisthocystis stepashi Timoshkin, Zaytseva et Gutsol sp. n.; Opisthocystis sturmbaueri Timoshkin, Zaytseva et Gutsol sp. n.; Opisthocystis kornilorum Timoshkin, Zaytseva et Gutsol sp. n.; Opisthocystis aleksandri Timoshkin, Zaytseva et Gutsol sp. n., and Opisthocystis igori Timoshkin, Zaytseva et Gutsol sp. n. Comparisons with other congeners are given. The species descriptions are supplemented by short notes about their ecology and distribution. For many years of investigations, all presently described species were found inhabiting the sandy bottom. Evidently, they should be considered as a specialized component of the psammophilous communities of the lake. The structure of systems of the majority of worms' organs is rather conservative and typical for Opisthocystis representatives (in particular, all new species have an unpaired caudal excretory vesicle of the protonephridial system with small species-specific differences in its structure). Another set of the species-specific characters is related to the size and structure of proboscis and, especially, to the structure of the male copulative apparatus. In particular, special attention is paid to the structure of the distal end of prostatic stylet. As a rule, each new species found is represented by several (in some cases, by several dozens) specimens; the stylet size and structure in the same species are also rather stable. The reasons for this unusual richness of Opisthocystis species in Lake Baikal and for the broad morphological diversification of the distal ends of their male prostatic stylets have not been yet clarified. Only one species of this genus, Opisthocystis goettei (Bresslau 1906), is known from freshwater of the Holarctic; in contrast, more than 30 species were described from Lake Baikal. Therefore, Lake Baikal should be considered as the largest and unique area of endemic speciation of Opisthocystis representatives.

Lake Baikal

Systematics, Taxonomy

Platyhelminthes

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