Selwynia madang Ng & Rahayu, 2016, n. sp.

Selwynia madang n. sp.

(Figs. 8–12)

Material examined. Holotype: ovigerous female (12.1 × 7.5 mm) (MNHN IU-2013-1428a), stn. PR142, west of Kranket Island, Madang, 05º11.8’S 145º49.2’E, 2–18 m, in terebellid worm tube (Loimia sp.), northeastern Papua New Guinea, coll. Expédition PAPUA NIUGINI, 30 November 2012. Paratypes: 1 male (8.2 × 5.4 mm) (MNHN IU-2013-1428b), same locality as holotype; 1 male (9.4 × 6.9 mm), 1 female (13.1 × 7.7 mm) (ZRC 2015.279), stn. PR186, west of Kranket Island, Madang, 05º11.3’S 145º49.5’E, 1–20 m, in terebellid worm tube, northeastern Papua New Guinea, coll. Expédition PAPUA NIUGINI, 5 December 2012.

Description (female holotype). Carapace (Fig. 8 A) oval, about 1.7 broader than long; dorsal surface smooth, region poorly demarcated, flattened to gently concave on mesogastric region, shallow, indiscernible pit on each hepatic region. Front (Fig. 8 C) deflexed, medially concave in dorsal view. Orbital margin (Fig. 8 C) entire, slightly narrower distally, without gap between cornea, external orbital angle. Anterolateral margin entire, convex laterally, not cristate, continuous with posterolateral margin. Epistome very short, medially sunken. Antennule folding transversely in fossa. Antenna with stout basal antennal article, not reaching distolateral angle of carapace; flagellum enters orbit. Ocular peduncles (Fig. 8 C) movable, short, stout, subconical, cornea small, well pigmented.

Third maxillipeds (Fig. 8 C) covering approximately three-quarters of buccal cavern when closed; ischium slightly longer, broader than merus; palp attached to distolateral angle of merus; exopod slender, tapering distally, reaching two-third length of merus; flagellum long.

Thoracic sternites 1, 2 fused, 2/3, 3/4 each demarcated by shallow ridge; sternites 4–8 laterally demarcated by shallow sutures, each medially interrupted; sutures between sternites 4/5, 6/7 longer than others; vulva small, ovate, situated on distal two-thirds of sternite 6.

Chelipeds (Fig. 8 C) equal. Merus triangular in cross section, dorsal margin rugose, dorsal margin, outer surface setose. Carpus smooth, inner angle absent. Chela with smooth surfaces, palm slightly longer than dactylus; immovable finger with weakly sinuous cutting edge, cutting edge convex medially, lined with small teeth; movable finger with cutting edge concave on distal half.

Ambulatory legs (P2–P5) (Figs. 8 A, 12G, H) relatively short; P3 longest, P5 shortest, setose on extensor, flexor margins; outer surface propodus, carpus with scattered short setae. Merus as long as or slightly longer than combined length of respective propodus, dactylus, extensor margin unarmed, flexor margin armature of P2–P5 as follows: P2 1+1-2/1+1-2, P3 1+3/1+3, P4 1+2-3/1+3, P5 0+0/0+0-1. Flexor margin of basis-ischium of P5 with distinct denticle. Dactylus very short, claw-like.

Abdomen (Figs. 8 B, 12F) with all somites, telson distinct, mobile; somites wide.

Description (male paratype). Carapace (Fig. 9 A) oval, about 1.4 broader than long; dorsal surface smooth, region poorly demarcated, flattened to gently concave on mesogastric region, shallow depression on each hepatic region. Front (Fig. 9 C) deflexed, medially concave in dorsal view. Orbital margin (Fig. 9 C) entire, slightly narrower distally. Anterolateral margin entire, convex laterally, not cristate, continuous with posterolateral margin. Epistome very short, medially sunken. Antennule folding transversely in fossa. Antenna with stout basal antennal article, not reaching distolateral angle of carapace; antenna enters orbit. Ocular peduncles (Fig. 9 C) movable, stout, subconical, cornea slightly protruding beyond orbit, small, well pigmented.

Third maxillipeds (Figs. 9 B, 12A) covering approximately three-quarters of buccal cavern when closed; ischium slightly longer, broader than merus; palp attached to distolateral angle of merus; exopod slender, tapering distally, reaching two-thirds length of merus; flagellum long.

Thoracic sternites 1, 2 fused, 2/3, 3/4 each demarcated by shallow ridge; sternites 4–8 laterally demarcated by shallow sutures, each medially interrupted; sutures between sternites 4/5, 6/7 longer than others, vulva on distal two-thirds of sternite 5, between mesial ends of suture 5/6, 6/7.

Chelipeds (Fig. 9 C) as in female.

Ambulatory legs (P2–P5) (Figs. 9 A, 12C) relatively short, P3 longest, P5 shortest, setose on extensor, flexor margins; outer surface propodus, carpus with short setae. Merus as long as or slightly longer than combined length of respective propodus, dactylus, flexor margin armature of P2–P5 as follows: P2 0+3/0+1-2, P3 0+3-4/0+3-4, P4 0+3-4/0+3-4, P5 0+0/0+0. Flexor margin of basis-ischium of P5 unarmed. Dactylus very short, claw-like.

Abdomen (Figs. 9 B, 12B) relatively wide, all somites, telson distinct, mobile, somite 1 widest. G1 (Fig. 12 D, E) slender, simple, slightly curved distally, slightly tapering at tip.

Colour. Males and females were dirty white in life, with the carapace of the females appearing yellowishorange because of the underlying organs (Figs. 10, 11). The legs and sides of the carapace are lined with light brown setae, and the corneas are orange-yellow (Figs. 9, 10). The specimens are often covered with brown dirt from the worm tube (Figs. 10 A, 11A).

Remarks. Selwynia madang n. sp., can be separated from all congeners by the shape of the third maxilliped. The merus of the third maxilliped of S. madang n. sp., is only slightly shorter or almost the same length (Fig. 12 A) while in other species the merus is clearly shorter than ischium (Figs. 4 A, 7A, 16A). Like S. sibogae, the flexor margin of the P2–P4 merus of S. madang n. sp., is armed with 1–4 teeth (Fig. 12 C, G). Compared to S. sibogae, S. madang n. sp., can also be distinguished by its relatively more slender G1 structure (Fig. 12 D, E) (distinctly stouter in S. sibogae; Fig. 4 D, E).

Biology. The specimens were all collected from a large terebellid polychaete worm which is provisionally identified as a species of Loimia (Fig. 11). One pair of worms were found in each tube (A. Anker, pers. comm.).

Distribution. Known only from eastern Papua New Guinea.