Bosmina japonica Poppe et Richard 1890

21. Bosmina japonica Poppe et Richard, 1890

Bosmina japonica Poppe and Richard 1890, p. 76 –77.

Not Bosmina cf. japonica in Ko ř ínek 1971, p. 292, figs 10F–H, 11A–D.

Type locality. "Lac Hakone, près Yokohama" (Poppe & Richard 1890), Honshu Island, Japan.

Richard's specimens. Lectotype (selected here): Parthenogenetic female in good state on slide with Richard number 174, labelled “ Bosmina japonica P.R., Hakone see bei Yokohama (M. Schmacker)”, USNM 1134576. Few females from sample DGF 0905, “Hakone. See bei Yokohama. Japan 5”.

Redescription. Parthenogenetic female. Body moderately compressed laterally in anterior view, relatively short and wide in lateral view, dorsal margin regularly curved from distalmost extremity to posterodorsal angle, posterior margin straight, its height more than half of body height, ventral margin almost straight, with a shallow depression anterior to mucro (Fig. 3A). Head without an ocular dome (Fig. 3B). Frontal head pore small, located far from ventral margin of head shield (as seen from anterior side) at level of antennular sensory setae (Fig. 3C–E). Fornices well-developed, covering coxal part of antenna II. Lateral head pore small, ovoid, located near ventral margin of head shield (Fig. 3F–G). Compound eye small, ocellus absent. Labrum a fleshy appendage lacking significant projections, distal labral plate small. Ventral valve margin with a series of stout setae on its anterior portion, base of each located on internal surface of valve (Fig. 3H). “Seta kurzi” located on internal side of valve anterior to abovementioned depression near mucro, mucro strong and long with truncated tip supplied with a system of minute indentations, and 1–3 incisions on ventral side (Fig. 3I), incisions absent from rare specimens with shortened mucro (Fig. 3J). Series of minute setules at inner side of valve near posterior valve margin.

Thorax relatively long, with 6 limb pairs. Postabdomen strongly compressed laterally, with width approximately equal along all its length, with ventral (although functionally dorsal) margin almost straight (Fig. 3K). Preanal margin long, slightly concave, with groups of setules distally. Sides of postabdomen supplied with series of finer setules. Distal (anal) margin truncated, postero-dorsal angle as a projection. Postanal portion as a cylindrical projection bearing paired postabdominal claws. Each claw regularly bent, with two pectens on concave (dorsal) margin, distal pecten consists of short spinules, while proximal pecten consists of 6–8 rather strong and thin teeth (Fig. 3L–M). Postabdominal seta somewhat shorter than preanal margin, its distal section about 1.5 times shorter than distal one.

Antenna I fused with rostrum, rather long, its length from tip to tip of rostrum about 0.5 body lengths. Antennular (frontal) sensory seta located on rostrum. Free section of antenna I (not incorporated into rostrum) consists of a pre-aesthetasc portion, fused with rostrum, and a post-aesthetasc portion (Kotov et al. 2009), regularly bent in this taxon. Pre-aesthetasc portion straight, regularly narrowing distad in anterior view, an internal spine near a flat site of origin of aesthetascs. Post-aesthetasc portion directed ventrally and posteriorly, remarkably curved in lateral view. Both portions supplied with dorsoventral series of fine denticles.

Antenna II typical for the genus, six pairs of thoracic limbs with morphology indistinguishable from that in other species (Kotov 1996, 1997a).

Ephippial female, male. Unknown.

Comments. No differences were found between B. japonica and B. longirostris (O. F. Müller, 1776); the latter is a very common species very widely distributed (Kotov et al. 2009). Kořínek et al. (1999) arrived at the same conclusion after a study of a topotypic specimen from Lake Hakone.