Manayunkia zenkewitschii Sitnikova, Shcherbakov & Kharchenko, 1997

Bick, Andreas & Bastrop, Ralf, 2025, Revision of the genus Manayunkia Leidy, 1859, and establishment of two subfamilies within Fabriciidae (Annelida, Sabellida), Zootaxa 5661 (1), pp. 1-58 : 40-42

Manayunkia zenkewitschii Sitnikova, Shcherbakov & Kharchenko, 1997

( Figure 22 )

Manayunkia zenkewitschii Sitnikova et al. 1997: 18–20 , fig. 1–10. – Pudovkina et al. 2016: 132–136.

Material examined. Russia, Lake Baikal : 55°25.833’N, 109°12.254’E, depth 11.1–12.5 m, coll. 27.07.2006, about 30 specimens ( ZSRO-P1941 ) .

Description (based on the description of Sitnikova et al. (1997) and own observations). Total length of specimens, including radiolar crown, between 2.5 and 4 mm (on average about 3 mm); width about 0.4 mm; length of radiolar crown between 0.5 and 0.6 mm; ratio between length of radiolar crown and body length, without radiolar crown, between 0.1 and 0.2; body slender, posteriorly rounded ( Fig. 22A ).

Radiolar crown with three pairs of radioles and one pair of unbranched vascularized ventral filamentous appendages; dorsal radioles unbranched, median and ventral radioles with more than 6 branches, about 22–38 branches in total, rarely 40–42 (on average about 28); no morphological differences in the structure of the branches, except ventral filamentous appendages; ventral filamentous appendages and almost all branches of radioles end usually at about same height, dorsal radioles sometimes shorter than branches of the middle and ventral radioles.

Peristomium distinctly longer than first chaetiger, with anterior and posterior rings; anterior margin of anterior peristomial ring as a low membranous collar ventrally, indented laterally, and narrowly separated mid-dorsally; border between anterior and posterior peristomial rings clearly visible; one pair of black peristomial eyes.

Chaetigers 1–6 each successively longer, chaetigers 7 and 8 successively shorter; abdomen about as long as chaetiger 4 or 5; margins of chaetigers 6 to 8 and of abdominal chaetigers often not clearly visible in adult specimens ( Fig. 22A ).

First chaetiger inferiorly with 2–4 short, and superiorly with 4–6 elongate, narrowly hooded notochaetae, neuropodial uncini absent. Notopodia of chaetigers 2–8 superiorly with about 4–6 elongate, narrowly hooded chaetae, about 0.4–0.5 mm long, and inferiorly with about 6–8 short, narrowly hooded chaetae, about 0.1–0.2 mm long ( Fig. 22B, C ); neuropodia of chaetigers 2–8 (male) or 2–5 (female) with 6–10 (on average 7) uncini, with main fang and apical with about 4–5 rows of progressively smaller teeth ( Fig. 22B, D ); neuropodia of females with 3–4 transitional chaetae or transitional uncini on chaetigers 6–8 ( Fig. 22E–G ); abdominal neuropodia with 2–4 narrowly hooded chaetae; abdominal notopodia with about 10–28 uncini; dentate region with about 6–8 rows of equal-sized teeth; dentate region about 15–18 µm long.

Brood chamber of females formed by bulge-like protrusions ventrally on chaetigers 6 and 8.

Pygidium rounded, not extended ( Fig. 22A ).

All chaetigers well pigmented.

Remarks. This is the smallest of the three Manayunkia species from Lake Baikal. Manayunkia zenkewitschii is characterized above all by an oval pygidium. The pygidium of the other two species from Lake Baikal is either elongated and pointed or triangular. In addition, in M. zenkewitschii all chaetigers are pigmented, in M. godlewskii ( Nusbaum, 1901) the pigment is almost completely absent, and in M. baicalensis ( Nusbaum, 1901) only the first 6 chaetigers are pigmented.

There is a sexual dimorphism in this species. Mature females have transitional chaetae and transitional uncini on neuropodia of chaetigers 6–8 instead of regular thoracic uncini. The presence of both transitional chaetae and transitional uncini is unique among the species of Manayunkia . Usually only one type of these particular chaetae is found on chaetigers 6 to 8 in females. A brood chamber, formed by bulge-like protrusions ventrally on chaetigers 6 and 8, is also present. Chaetigers 6 to 8 are slightly elongated in mature males. Both characters are also found in M. baicalensis and M. godlewskii (see Sitnikova et al. 1997).

Geographic distribution. Known only from Lake Baikal, Russia.

Biology. The eggs deposited in the tube of the females have a length of about 220–290 µm and a width of 150–180 µm. A maximum of 18 developmental stages, eggs and embryos, can be observed simultaneously in the tubes. The main reproduction period is in June. However, females with eggs have also been found in February and March ( Sitnikova et al. (1997).

Ecology. The specimens of this smallest Baikal species mainly settle on stones and rocky ground, which can also be covered with sponges or algae, but also on sand with algae and on empty tubes of caddisflies ( Pudovkina et al. 2016, Sitnikova et al. 1997).

Figures

FIGURE 22. Manayunkia zenkewitschii Sitnikova, Shcherbakov & Kharchenko, 1997, SEM micrographs. A. Posterior end, lateral view. B. Parapodium of chaetiger 2. C. Notopodium of chaetiger 3. D. Thoracic uncini of chaetiger 2. E. Parapodium of chaetiger 6, with transitional chaetae in the position of thoracic uncini. F. Parapodium of chaetiger 7, with transitional chaetae in the position of thoracic uncini. G. Parapodium of chaetiger 8, with two transitional chaetae and one transitional uncinus in the position of thoracic uncini. Scale bars. A 100 µm, B, C, E–G 20 µm, D 5 µm.