Bosminopsis cf. africanus (Daday, 1908)

(Figs. 1–2)

Material examined here. Many parthenogenetic females and three males from a large un-named reservoir, South Vietnam (10.459098 °N, 104.937477 °E) collected on 07.04.2023 by A.A. Kotov, P.G. Garibian and Vietnamese colleagues. Sample is now kept in the research collection of A.A. Kotov, A.N. Severtsov Institute of Ecology and Evolution, Moscow, Russia, accession number AAK M-7790 .

Parthenogenetic female. Morphology (Fig. 1A–D) fully conforms to that described earlier for other populations from SE Asia (Garibian et al. 2021b).

Description of adult male. Body (Fig. 1E–F) short, transparent (width to length ratio 0.66–0.67). Dorsal margin of body humpbacked, dorsal margin of carapace straight.

Head (Fig. 1G–H) relatively large, with a smooth rostrum, eye relatively large, labrum rounded and naked.

Valves. Posterior portion straight. Postero-ventral angle with a single long seta (seta Kurzi) and a single welldeveloped mucro (Fig. 2D: arrow), but sometimes the latter absent in largest adults (Fig. 2C: arrow). Ventral valve portion with several short spines.

Antenna I (Fig. 2A) movable, frontal sensory seta attached somewhat closer to base than tip. On inner margin of its proximal part, there are three tufts of short setulae and a short male seta. Distal part with nine aesthetascs of subequal size, and few minute spines located at the inner margin.

Antenna II with a single seta on coxopodite (Fig. 2B, arrow) its length c.a. 1/3 basal segment length. Apical seta of basal segment (Fig. 2B, arrow) relatively long (longer than proximal endopod segment). Distal endopod segment bears a long additional seta (Fig. 2B, arrow).

Postabdomen (Fig. 2E) as in parthenogenetic female, ventral edge slightly curved, preanal and anal margins straight, postanal angle absent. Postabdominal claw bears a single basal spine comparable in size with the former.

Limb I (Fig. 2F–G) with outer distal lobe bearing two setae of different size, inner distal lobe with a copulatory hook and a seta (Fig. 2F–G: arrow). Inner distal lobe of limb III (Fig. 2H) as in parthenogenetic female: it bears six soft setae.

Size. In our material, female length 0.19–0.4 mm, adult male length 0.29–0.31 mm.

Key for species identification within B. deitersi species group based on adult male morphology

1(2) Postero-ventral portion of valves with several, long mucro-like spine (better expressed in juveniles).. B. zernowi Linko, 1901

2(1) Postero-ventral portion of valves with a single, relatively short mucro........................................... 3

3(4) Limb I corm without a seta near ejector hooks........................................... B. deitersi Richard, 1895

4(3) Limb I corm with an additional seta near ejector hooks................................. B. cf. africanus Daday, 1908