Selwynia edmondsoni (Rathbun, 1932)

Ng, Peter K. L. & Rahayu, Dwi Listyo, 2016, On the genera Selwynia Borradaile, 1903, and Gandoa Kammerer, 2006, with descriptions of two new species from Papua New Guinea and French Polynesia (Crustacea: Decapoda: Brachyura: Aphanodactylidae), Zootaxa 4092 (3), pp. 339-370 : 348-352

Selwynia edmondsoni (Rathbun, 1932)

( Figs. 5–7 )

Aphanodactylus edmondsoni Rathbun, 1932: 181 ; Edmondson 1946: 113, 303, fig. 182; Edmondson 1962: 6, figs. 2d, 3; Schmitt et al. 1973: 127; Titcomb et al. 1979: 366; Hoover 2006: 85; Ng et al. 2008: 247; Ng & Naruse 2009: 284; Ahyong & Ng 2009: 36; Ng et al. 2010: 76; Castro 2011: 124.

Material examined. Holotype: female (16.1 × 9.5 mm) (BPBM 3576), O‘ahu, Hawai‘i, coll. C.H. Edmondson. Others: 1 male (11.6 × 8.0 mm) (BPBM 3577), Waimanalo, O‘ahu, Hawai‘i, coll. C.H. Edmondson, 27 November 1931; 1 male (10.8 × 8.1 mm), 1 female (16.5 × 10.0 mm) (ZRC 2000.0542), O‘ahu, Hawai‘i, coll. C.H. Edmondson, 1930s.

Redescription (female). Carapace ( Fig. 5 A) oval, about 1.7 broader than long; dorsal surface smooth, region poorly demarcated, flattened to gently concave on mesogastric region, pit on each hepatic region. Front ( Fig. 5 B) strongly deflexed, medially concave in dorsal view. Orbital margin ( Fig. 5 B) entire, slightly narrower distally, narrow gap between cornea, external orbital angle. Anterolateral margin entire, convex laterally, not cristate, continuous with posterolateral margin. Epistome 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. 5 B) movable, short, stout, subconical, cornea small, well pigmented.

Third maxillipeds covering approximately four-fifths of buccal cavern when closed; ischium longer, broader than merus; exopod slender, reaching proximal margin of merus; flagellum long.

Thoracic sternites 1, 2 fused; sternites 2/3 separated by shallow suture; sternites 4–8 laterally demarcated by shallow sutures; sutures between sternites 4/5, 6/7 longer than others; vulva large, ovate, on distal two-thirds of sternite 6, almost as broad as sternite.

Chelipeds equal. Merus triangular in cross section, unarmed, ventrolateral margin with sparse setae. Carpus smooth, inner angle absent. Chela with smooth surfaces, palm about 1.1 times longer than dactylus; fingers crossed at tip when closed.

Ambulatory legs (P2–P5) ( Figs. 5 A, C, 7H) relatively short, P3 longest, P5 shortest; extensor surface glabrous, long, plumose setae on margins, flexor surfaces of carpus, propodus. Merus as long as or slightly longer than combined length of respective propodus, dactylus, extensor with small denticles proximally; flexor margin armature of P2–P5 as follows: P22+1/2+1, P3 2+3/2+3, P4 1+2/2+1, P5 1+1/1+3. Flexor margin of basis-ischium of P5 unarmed. Dactylus very short, claw-like.

Abdomen ( Figs. 5 C, 7I) with all somites, telson distinct, mobile; somites wide.

Description (male). Carapace ( Fig. 6 A) subquadrate, about 1.5 broader than long; dorsal surface smooth, regions poorly demarcated, shallow deep depression on each hepatic regions, cardiac, intestinal regions distinct. Front ( Fig. 6 C) deflexed, medially concave in dorsal view. Orbital margins ( Fig. 6 C) entire, oval, no gap between cornea, external orbital angle. Epistome ( Fig. 6 C) longer than that of female, posterior margin slightly concave. Antennule, antenna as in female. Eyes ( Fig. 6 C) short, stout, with distinct cornea.

Third maxillipeds ( Figs. 6 B, 7A) covering four-fifths of buccal cavern when closed; similar to female third maxillipeds except for more rounded distomesial angle.

Thoracic sternites 1, 2 fused, sternites 2/3 separated by deep suture, sternite 3/4 fused; sternites 4–8 demarcated by shallow, narrow sutures, press button of abdominal locking mechanism present on distal of sternite 5; penis emerging from near anterior border of sternite 8.

Chelipeds ( Fig. 6 D, E) relatively strong, slightly unequal in size. Merus triangular in cross section, ventroouter margin granulated, dorsal margin rugose, dorsal margin, outer surface setose. Carpus smooth, inner angle rounded. Chelae, ambulatory legs ( Figs. 6 D, E, 7C–E) as in female, except for armature of lower margins of ambulatory merus.

Extensor margin smooth except for P4 merus with row of denticles proximally; flexor margin armature of P2– P5 merus as follows: P2 1+2/1+0, P3 1+2/1+1, P41+5/1+4, P5 1+3/1+2; P4 merus anterior margin of extensor surface with 3 teeth. Flexor margin of basis-ischium of P5 unarmed. Dactylus very short, claw-like.

Abdomen ( Figs. 6 B, 7B) with all somites, telson distinct, mobile, relatively narrow, somite 1 broadest, somite 3 to telson forming straight lateral margins. G1 ( Fig. 7 F, G) simple, proximal five-sixths straight, distal one-sixth slightly twisted.

Colour. There are no notes on colour in life.

Remarks. Selwynia edmondsoni resembles S. punctata n. sp., and both species have one strong proximal spine on the flexor margin of the P5 merus for both sexes. In male S. edmondsoni , however, the strong spine is followed by row of small denticles ( Fig. 7 E) (more entire in S. punctata n. sp.; Fig. 16 D). The distal half of the G1 is slightly twisted in this species ( Fig. 7 F, G), a unique character among Selwynia species.

Biology. All the known specimens of S. edmondsoni were collected from terebellid worms. Edmondson (1962: 6) writes “In 1931 a pair of crabs (male and female) representing the Pinnotheridae was taken from a tide pool on the Waimanalo shore of Oahu. They were occupying the shelly tube enclosing a large terebellid worm. The tube, about 12 inches long and attached to the underside of a flat stone, was in 8 inches of water at low tide. Rathbun recognized these crabs as representatives of the genus Aphanodactylus and a new species, A. edmondsoni .”

Distribution. Hawaiian Islands.

Figures

FIGURE 5. Selwynia edmondsoni (Rathbun, 1932), female holotype (16.1 × 9.5 mm) (BPBM 3576), O‘ahu, Hawai‘i. A, overall habitus; B, subfrontal view of cephalothorax; C, ventral view of cephalothorax showing abdomen.

FIGURE 6. Selwynia edmondsoni (Rathbun, 1932), male (10.8 × 8.1 mm) (ZRC 2000.0542), O‘ahu, Hawai‘i. A, overall habitus; B, ventral view of cephalothorax; C, frontal view of cephalothorax; D, outer view of left chela; E, outer view of right chela.

FIGURE 7. Selwynia edmondsoni (Rathbun, 1932). A – G, male (10.8 × 8.1 mm) (ZRC 2000.0542); H, I, female (16.5 × 10 mm) (ZRC 2000.0542); both O‘ahu, Hawai‘i. A, left third maxilliped; B, male abdomen; C, left P 4 (inner view); D, left P 4 (outer view); E, right P 5; F, G, left G 1; H, right P 5; I, female abdomen. Scales = 1.0 mm.

FIGURE 16. Selwynia punctata n. sp. A – F, male paratype (4.3 × 3.3 mm) (ZRC 2015.280), G – I, ovigerous female holotype (7.0 × 4.0 mm) (UF); both Moorea, French Polynesia. A, left third maxilliped; B, male abdomen; C, right P 2; D, right P 5; E, F, left G 1; G, female abdomen; H, right P 4 (setae not drawn); I, right P 5 (setae not drawn). Scales: A, C – F = 0.5 mm; B, G = 1.0 mm.