Anisarthrus okunoi sp. nov.

[Japanese name: Sarasa-no-harayadori]

(Figs 1–3)

Material examined. Holotype: ovigerous female (BL 3.88 mm), KMNH IvR 500,727, removed from ventral surface of pleon of hinge-beak shrimp Rhynchocinetes uritai (female, CL 6.98 mm), CMNH-ZC 02342, Yura Harbor (34°17′30″N, 134°57′00″E), Sumoto city, Awaji Island, Hyogo Prefecture, central Japan, 6 m depth, 22 October 2008, coll. J. Okuno, K. Hanano, and T. Tamego. Allotype: male (BL 1.12 mm), KMNH IvR 500,728, removed from pleon of holotype female.

Description of holotype female (KMNH IvR 500,727). Body (Fig. 1A, B) markedly asymmetrical, greatly expanded on convex (left) side, approximating an inverted equilateral triangle in general outline; body axis distortion about 40º; maximal body width about 1.2 times as long as body length.

Head (Fig. 1A) quadrilateral, completely embedded in pereon, representing about 35% of body length; frontal margin concave and deeply cleft. Eyes absent. Right antenna 1 (Fig. 2A) of 3 articles, articles 2 and 3 with distal and terminal setae, respectively; right antenna 2 (Fig. 2B) of 5 articles, of which articles 2, 3, and 4 with marginal and distal setae, article 5 with terminal setae. Right and left maxillipeds (Fig. 2C, D) symmetrical, semi-ovoidal, nearly straight medially, roundly angled anteriorly, without palp, bearing short spur; anterior article about 2.4 times as long as posterior article. Barbula (Fig. 2E) with pair of short, stout lateral projections, its lateral margins expanded and mid-region produced slightly into medial point.

Pereon (Fig. 1A): pereomeres 1 and 2 completely distinct dorsally; pereomeres 3–7 distinct on concave (right) side and medially but segmental boundaries not clearly expressed on convex (left) side. All pereomeres with dorsolateral bosses on concave side. Inflated closed brood pouch (Fig. 1B) expanded far laterally, formed of fused convex oostegites 2–5. Oostegite 1 of convex side (Fig. 2F) bilobed; that of concave side (Fig. 2G) oval, not segmented, lacking posterolateral point. Oostegites 2–5 of concave side all separated and aligned. Seven pereopods on each side of body; on both sides, first two pairs of pereopods adjacent to head: both pairs large and with all articles distinct, basis rectangular, ischium trapezoidal and shorter than basis, merus trapezoidal with short spines on inferior margin, carpus triangular, propodus ovate, dactylus stout (Fig. 2H). Pereopods 3 and 4 of convex side widely separated by expanded part of pereomere (Fig. 1A). Pereopods 5–7 present on posterior margin of pleon, covered by left pleopod 1 (Fig. 2I). Pereopods 3–7 of concave side tightly clumped (Fig. 1A).

Pleon (Fig. 1 A–C): all pleomeres fused dorsally; pleomeres 1–4 distinct laterally and ventrally; pleomere 1 bearing single midventral tubercle, pleomere 2 with two similar ventral tubercles; pleomere 5 (= pleotelson) in form of simple bulb visible only in ventral view. Four pairs of large lamellar lateral plates and four pairs of pleopods present, all well-developed; lateral plates (Fig. 1A) irregularly oval, shorter posteriorly; those on concave side smaller than those opposite. Pleopods (Fig. 1C) uniramous, first two large, lanceolate; pleopods 3 and 4 slightly bilobed and smaller than pleopods 1 and 2. Uropods absent.

Description of allotype male (KMNH IvR 500,728). Body (Fig. 3 A–C) small, about 29% as long as female, elliptical in general outline; body width 54% of body length, with maximal width at pereomere 5.

Head (Fig. 3A) distinct from pereomere 1, semicircular, with tiny medial notch on anterior margin, slightly longer than pereomere 1. Eyes absent. Antenna 1 (Fig. 3D) short, of 3 articles; articles 2 and 3 each with tuft of long seta distally. Antenna 2 (Fig. 3D) of 7 articles, surpassing midpoint of pereomere 1.

All pereomeres (Fig. 3 A–C) distinctly demarcated dorsally, lacking tubercles ventrally; lateral margins convex; pereomere 7 and pleon distinct laterally on both sides, fused in central region both dorsally and ventrally. Pereopods (Fig. 3E) all of similar size and structure; all articles similar to those of female in segmentation.

Pleon (Fig. 3A, C) completely fused, semi-ovoidal, representing 27% of whole body length; posterior margin rounded, smooth, without anal tube or long taper. Pleopods and uropods absent.

Etymology. Named in honour of the collector, Dr. Junji Okuno, in recognition of his contribution to the knowledge of the hinge-beak shrimps.