Manayunkia athalassia Hutchings, Deckker & Geddes, 1981

(Figures 3 top right, 9–10, 26B)

Manayunkia athalassia Hutchings et al., 1981: 25–27, fig. 1.

Material examined. Western Australia, Yalgorup National Park, Lake Newnham, 32°54’06.1’’S, 115°41’47.0’’E, coll. 24.01.2014,> 50 specimens (WAM-V8215 and WAM-V8216).

Description. Total length of specimens, including radiolar crown, between 2.5 and 3.2 mm (but see Remarks); width on chaetiger 2 about 0.3 mm (but see also Remarks); length of radiolar crown max. 0.65 mm; ratio between length of radiolar crown and body length, without radiolar crown, between 0.2 and 0.25; body slender, slightly tapering posteriorly (Figs 3, 9A, I).

Radiolar crown with three pairs of radioles and one pair of unbranched vascularized ventral filamentous appendages (Figs 9A, 10A, B, 26B); surface of radioles and ventral filamentous appendages usually wrinkled (Fig. 9A, but see Fig. 10A); first dorsal radioles branch off from the branchial lobe, median and ventral radioles arise from a common base (Fig. 10B–F); all radioles asymmetrical branched or pectinated (Fig. 10A–F, 26B); ventral radioles with 5–7, median and dorsal radioles with 4–6 branches (Fig. 10B–D, 26B); smaller specimens with only 2–3 branches per radiole; no morphological differences in the structure of the various branches of the radiolar crown, except ventral filamentous appendages (Fig. 10B–F, 26B); ventral filamentous appendages and branches of radioles end at about the same height or ventral filamentous appendages slightly longer (see Figs 9A, 10A); branches of radioles rectangular to square in cross-section, extension about 20–30 x 27–40 µm; vascularized ventral filamentous appendages oval, extension about 45–65 µm (Fig. 10B–D); blood vessel in ventral filamentous appendages (Fig. 10B–D); epidermis of radioles and vascularized ventral filamentous appendages adorally with ciliated and aborally with non-ciliated epthelial cells; ciliated cells constitute the food groove; center of branches of radioles occupied by a large cavity bordered by a narrow band of cells; dorsal lips developed as triangular lobes, rounded at upper margin, about 50–70 µm long, dorsal lips connect dorsal radioles with vascularized ventral filamentous appendages (Fig. 10D–F).

Peristomium slightly longer than first chaetiger, about as long as chaetiger 2, with anterior and posterior rings (Fig. 9A); anterior peristomial ring distinctly shorter than posterior ring (Fig. 9A); anterior margin of the anterior peristomial ring developed as a low membranous collar ventrally, narrowly separated mid-dorsally; ciliated band present ventrally on posterior margin of anterior peristomial ring (Figs 9A, 10A); border between anterior and posterior peristomial rings clearly visible (Figs 9A, 10A). Faecal groove dorsally deeply sunken in peristomial region, becoming considerably lower on first and following chaetigers; faecal groove shifts from dorsal to ventral midline at border between thorax and abdomen (Fig. 9I).

Metanephridia located in peristomium and first 2 chaetigers. First chaetiger shorter than peristomium and second chaetiger; chaetigers 2–6 each successively longer, chaetigers 7 and 8 successively shorter; first thoracic chaetigers wider than long, last 3 or 4 thoracic chaetigers distinctly longer than wide; abdominal chaetigers short, chaetiger 9 longest, chaetiger 10 and 11 decreasing in length (Figs 3, 9I); pygidium about same length as chaetiger 10, terminating as rounded lobe or tapered; pygidial eyes absent; borders between thoracic chaetigers usually clear visible (Figs 3, 9A).

First chaetiger with about 1–2 short, and 2–3 elongate, narrowly hooded notochaetae, neuropodial uncini absent; notopodia of chaetigers 2–5 superiorly with 3–4 elongate, narrowly hooded and inferiorly with 2–3 pseudo-spatulate chaetae (Fig. 9D); notopodia of chaetigers 6–8 superiorly with 3–4 elongate, narrowly hooded and 2–3 short, narrowly hooded chaetae (Fig. 9E, G); neuropodia of chaetigers 2–5 (female) or 2–8 (male) with 4–6 (rarely 2, 3 or 7) uncini with main fang and apical with about 6–8 rows of progressively smaller teeth (Fig. 9B); mature females with 4–6 transitional uncini on chaetigers 6–8, different from thoracic uncini on chaetigers 2–5 (Fig. 9C, F, G); transitional uncini almost same size as regular thoracic uncini, main fang only indistinctly developed, i.e., less acute and more rounded, with a multitude of rows of small, almost equal-sized teeth (Fig. 9C); abdominal neuropodia with 3–5 elongate, narrowly hooded chaetae (Fig. 9I); abdominal notopodia with 16–20 uncini on chaetiger 9, 15–20 on chaetiger 10, and 10–13 on chaetiger 11, respectively (Fig. 9H); abdominal uncini with about 5–6 rows of equal-sized teeth, about 4–6 teeth per row (Fig. 9H); manubrium about three times as long as dentate region.

Posterior end of pygidium tapered or rounded (Figs 3, 9I).

Radiolar crown and thorax greenish-black or brownish-green until chaetiger 6, then transparent; intestine dark coloured.

Remarks. Manayunkia athalassia is the only Manayunkia species with branched dorsal radioles. In all other species the dorsal radioles are unbranched (see Table 2). The specimens studied here were collected in Western Australia. Compared to the individuals from the type locality in South Australia, these individuals are somewhat smaller (3.2 mm long vs. 5 mm long, and 0.3 mm wide vs. 0.5 mm wide). In contrast, the number of thoracic and especially abdominal uncini is significantly greater. The specimens from the type locality have only 10–12 abdominal uncini per chaetiger. It is remarkable since larger specimens usually have more hooks and chaetae. Smaller specimens of M. athalassia have about 30 uncini per body side in the three abdominal chaetigers, whereas adults have slightly more than 50. It must therefore be clarified whether the specimens from South and Western Australia actually belong to one species.

There is a sexual dimorphism in this species, or it could be a simultaneous hermaphrodite (Rouse et al. 2024). In females, transitional uncini were found on chaetigers 6–8 (see Remarks for other species). These uncini differ very little from the regular thoracic uncini. This may explain why this type of uncini has not been mentioned in the original description by Hutchings et al. (1981). It is not known if females of this species have a brood chamber.

Geographic distribution. This species occurs in ephemeral hypersaline salt lakes in South and Western Australia.

Biology. Manayunkia athalassia lives in colonies of up to 20 individuals (Hutchings et al. 1981).

Females with oocytes about 250x100 µm in size were found in February and males with spermatocytes in March. The oocytes develop in chaetiger 4, and the spermatocytes in chaetiger 7 (Graeme Christie, pers. comm.)

Ecology. Manayunkia athalassia lives in hypersaline lakes at salinities between 22 and 95 psu. Graeme Christie (pers. comm.) observed living specimens, motionless but still alive even at 185 ppt. In summer, these lakes can dry up and the temperature exceeds 40 °C. The specimens then fall into a kind of rigidity or suspended animation. They could also be maintained in an aquarium of 82 psu for several month. The specimens occur in gelatinous tubes in soft clayed carbonate sediments which may contain shell debris of ostracods and gastropods (Hutchings et al. 1981).