Pseudorhynchelmis olchonensis ( Burow et Koshow, 1932 )

Martin, Patrick & Kaygorodova, Irina, 2008, A new species of Pseudorhynchelmis Hrabě, 1982 (Clitellata: Lumbriculidae) from Lake Baikal, with re-descriptions of P. parva and P. olchonensis, Zootaxa 1938, pp. 23-39 : 32-35

Pseudorhynchelmis olchonensis ( Burow et Koshow, 1932) ( Figure 4)

Rhynchelmis olchonensis Burow et Koshow, 1932: 83 –84, non sensu Hrabė, 1982: 190 –191. Type reference. Rhynchelmis olchonensis Burow et Koshow, 1932: 83 –84

Synonymy. Rhynchelmis dissimilis Semernoy, 2004: 408 –412, partim, Figs. 226, 227 (non figs 228, 229).

Type material. Types not seen by the authors. Although not mentioned in Burow & Koshow (1932), type material should have been deposited in the Limnological Institute of Irkutsk, Siberian Branch of the Academy of Sciences, Russia. In spite of our efforts, we were unable to lay hands on type material, which should thus be considered as lost.

Neotype. One mature specimen ( LISB slide 97.80.51), incomplete (first 18 segments), anterior ends (head and sexual segments) cut along the midsagittal plane, tail left as is, stained in alcoholic carmine and mounted in Canada balsam.

Paraneotype. Two specimens partially mature ( LISB slides 97.80.42, 97.80.16), incomplete (first 15 and 14 segments, respectively), dissected and mounted in the same way.

New material deposited in the Limnological Institute of Irkutsk, Siberian Branch of the Academy of Sciences ( LISB).

Locality. Lake Baikal, Southern basin, Murino bank; 51° 30’ 07” N, 104° 29’ 06” E); 25–27 September 1997; at 18 m depth (net sampling); sandy sediment with big separate stones obstructing dredging or grabbing.

Description. Medium-sized species (incomplete specimens, 14–18 segments, 2.6–4.2 mm), breadth 363–530 µm at widest (clitellum). Prostomium rounded. No secondary segmentation discernible, intersegmental annulation scarcely marked in postclitellar segments. Clitellum extending over ½ IX–½ XII. Two single-pointed setae per bundle, sigmoid, with bent tips, similar in dorsal and ventral bundles, 62–106 µm long, 2–3 µm thick nodulus on the ectal third of seta ( Fig. 4B). (1)2 modified penial setae per bundle in X, 114–160 µm long, 5 µm thick, elongate, straight, cane-like curved entally, nodulus proximal to the middle of shaft’s length, on the ental third of seta, ectal tip slightly grooved longitudinally ( Fig. 4B; Fig. 4A, gs). Setal length increasing from 62 µm in II to 87–106 µm in V–IX, slightly decreasing to nearly constant length (69–79 µm) in postclitellar segments.

Dorsal pad of pharynx extending from II to III, pharyngeal glands in II–VII. Anterior and posterior sperm sacs confined to X or extending to XI, respectively ( Fig. 4A, sps). Egg sacs not visible. One pair of spermathecal pores opening in the middle of VIII, on the same line as ventral setae and behind them. Slit-like spermathecal pores, laterally flanked by well-developed, flat papillae ( Fig. 4A, spp). Long and tubular spermathecal ducts ( Fig. 4A, spd), proximally opening into narrow vestibulae ( Fig. 4A, spv), distally penetrating to IX and leading to roughly spherical ampullae ( Fig. 4A, spa) confined to IX or extending to X. Sperm as an amorphous mass in ampullae. No communication between spermathecal ampullae and gut cavity.

Two pairs of testes in IX and X, attached ventrally to septa 8/9 and 9/10, respectively ( Fig. 4A, t). Male pores paired, in line with ventral setae, opening ventrally, behind and just beside glandular pores from which stand out penial setae ( Fig. 4A, mp). Two pairs of sperm funnels on septa 9/10 and 10/11, respectively ( Fig. 4A, sf), similar in size; sperm funnels directed in opposite directions, the anterior ones towards anterior segments, the posterior ones backwards, within posterior sperm sacs. Two pairs of vasa deferentia ( Fig. 4A, vd). Anterior vas deferens running on the floor of X with some loops, posterior vas deferens entering into XI and making a loop outside sperm sacs before turning back to X, both accompanying atrium proximal to this and opening into atrium subapically. Vasa deferentia 21 µm wide; half as wide (11 µm) proximal to atria. Tubular, elongate atria, 422 µm long, 46 µm wide. Atrial ampullae with 6 µm wide muscular coat, penetrating into posterior sperm sacs in XI ( Fig. 4A, a). Proximal part of atria modified into extensible ejaculatory ducts, operated by well-developed muscles ( Fig. 4A, m). No penes visible in the available material. No rudimentary atrium. Prostate glands discrete, elongate, sparsely covering atria and separately opening onto atrium by means of short ducts ( Fig. 4A, pr). One pair of massive accessory copulatory glands ( Fig. 4A, cgl), surrounding penial setae and opening ventrally by small pores surrounded by tall epidermal cells, in line with, and just before, male pores.

Female pores paired, opening onto intersegmental furrow XI/XII, in line with setae and spermathecal, glandular and male pores. Female funnels well developed (180 µm tall), ciliated, located in XI and standing against septum 11/12 ( Fig. 4A, ff). Ovaries paired, attached ventrally near septum 10/11, restricted to XI (no mature oocyte).

Remarks. Only one penial seta per bundle is present in the fully mature specimen LISB 97.80.51, in contrast to the other two partly mature specimens where 2 penial setae per bundle are noticeable. As some other setal bundles nearby genital segments of the mature specimen have only one seta also, it seems likely that missing setae were lost, by accident or as a result of copulation, and that two penial setae per bundle is the common setal pattern.

The present specimens fit the original description of P. olchonensis ( Burow & Koshow, 1932) in every respect but penial setae and small retractile penes. Unfortunately, there is no way to check these distinctive characters in type specimens of P. olchonensis , and we are reduced to making hypotheses as to their state in the types.

In most Pseudorhynchelmis species, penes look as a simple extension of atrial ducts and are usually small and pendant, in reduced penis sacs. The only one fully mature P. olchonensis specimen available for this redescription shows a blurred picture of the morphological organisation at the male pore, so that we cannot exclude that small retractile penes do exist. As to penial setae, one can speculate that they were present in type specimens but were overlooked by Burov and Kozhov, all the more easily since genital setae were completely unknown in the family Lumbriculidae at that time. Supporting this hypothesis is the description by Burov and Kozhov of a large number of pear-shaped glandular cells surrounding ventral setae in X (“…Die ventrale Borstensäcke im 10. Segment sind von einer grossen Menge birnenförmiger Drüsenzellen umringt…”; Burow & Koshow, 1932: 84). Although this character plays a key role in the identification of P. olchonensis , it was surprisingly omitted in later descriptions (i.e. Chekanovskaya, 1962). Accessory copulatory glands are known in lumbriculids, especially Lamprodrilus species ( Cook, 1971) but they are not associated with ventral setae. In contrast, there are many examples of developed glandular cells associated with genital setae in other families, probably resulting from a modification of setal glands (e.g. Martin & Brinkhurst, 1998). The glandular structure mentioned in the original description of P. olchonensis perfectly fits the description of copulatory glands associated with penial setae in P. alyonae and the present specimens of P. olchonensis . As a result, it seems reasonable to argue that, in all probability, original types of P. olchonensis might have had penial setae and that our specimens belong to this species.

Subsequent to a re-examination of Hrabĕ’s material, Martin et al. (1998) put Pseudorhynchelmis olchonensis sensu Hrabĕ (1982) in synonymy with P. shamanensis . In spite of this, Semernoy (2004) attributed P. olchonensis sensu Hrabĕ (1982) to P. olchonensis ( Burow & Koshow, 1932) , without a re-examination of Hrabĕ’s material. In contrast to the neotype and paraneotypes presently described, Hrabĕ’ specimens do not have either modified genital setae or accessory copulatory glands; male pores are distinctly median to the ventrolateral setae, and they have distinct penes in sacs. As a result, the validity of Martin et al. ’s decision is here reasserted.

P. olchonensis is distinct from all other Pseudorhynchelmis species by the slit-like openings of spermathecal pores laterally flanked by well-developed papillae, and penial setae opening just in front of male pores. Similar spermathecal pores are known in P. p a r v a but, in that case, there is a clear thickening of cuticle and spermathecal papillae are absent. P. alyonae is probably the closest to P. olchonensis . They are similar in many respects if only for their genital setae. However, in P. alyonae , atria extend behind segment XI (up to XII, inclusively) and male pores are separated from copulatory gland pores by a distance roughly similar, or slightly inferior to the length of the penial setae ( Fig. 1A in Martin et al., 1998). Similar spermathecal papillae are present in both species although more developed in P. a l y o n a e, but spermathecal ducts proximally open through massive bulbs in P. alyonae , in contrast to small vestibulae of P. olchonensis .

Geographical distribution and habitat. To date, only known from Lake Baikal, Maloye More (Olkhonskiye varota) and Murino bank (southern basin; 18 m), both localities +/- 250 km from each other.