Agononida isabelensis, Cabezas & Macpherson & Machordom, 2009

Cabezas, Patricia, Macpherson, Enrique & Machordom, Annie, 2009, Morphological and molecular description of new species of squat lobster (Crustacea: Decapoda: Galatheidae) from the Solomon and Fiji Islands (South-West Pacific), Zoological Journal of the Linnean Society 156 (3), pp. 465-493 : 467-469

AGONONIDA ISABELENSIS SP. NOV. ( FIG. 1 )

Material examined: Solomon Islands. SALOMON 1. Stn 1801, 09°25.0′S, 160°25.9′E, 1 October 2001, 254– 271 m: 1 M, 20.7 mm (holotype, MNHN-Ga6496); 3 M, 14.0– 20.7 mm; 3 ov. F, 17.2–18.4 mm (paratypes, MNHN-Ga6497). Stn 1802, 09°31.1′S, 160°35.0′E, 2 October 2001, 245– 269 m: 2 M, 14.0– 14.4 mm (paratypes, MNHN-Ga6498). Stn 1803, 09°32.1′S, 160°37.3′E, 2 October 2001, 308– 347 m: 1 M 17.6 mm (paratype, MNHN-Ga6499). Stn 1860, 09°22′S, 160°31′E, 7 October 2001, 620 m: 5 M, 6.8–16.0 mm; 3 F, 7.2–14.4 mm (paratype, MNHN-Ga6500) .

SALOMON 2. Stn 2210, 07°33.5′S, 157°42.3′E, 26 October 2004, 240– 305 m: 11 M, 6.9–19.0 mm; 3 ov. F, 14.1–15.1 mm; 3 F, 9.4–11.5 mm (paratypes MNHN- Ga6501). Stn 2287, 8°39.84′S, 157°23.505′E, 6 November 2004, 253– 255 m: 2 juv., 5.3–5.5 mm (paratypes, MNHN-Ga6502).

Etymology: From Isabel, one of the Solomon Islands from which some of the specimens were collected.

Description: Carapace as long as wide. Transverse ridges usually interrupted in cardiac and branchial regions by dense, short non-iridescent setae. Gastric region with two epigastric spines; one median cardiac spine and one postcervical spine on each side. Posterior border of carapace unarmed. Frontal margins transverse, slightly concave. Lateral margins slightly convex. Anterolateral spine strong at anterolateral angle, reaching or overreaching the level of the sinus between the rostrum and the supraocular spines. Second marginal spine before cervical groove 0.3 of the preceding one. Branchial margins with three spines. Rostrum spiniform, nearly half as long as remaining carapace, straight, and horizontal. Supraocular spines (right spine regenerating in holotype) slightly thicker than rostral spine, clearly overreaching midlength of rostrum, and exceeding ends of corneas, slightly divergent, directed slightly upwards ( Fig. 1A ).

Thoracic sternites with numerous short striae. Anterior part of fourth sternite slightly narrower than third; median part of posterior margin of third sternite contiguous to fourth sternite. Transverse ridges between fifth, sixth, and seventh sternites obtuse, feebly granulated ( Fig. 1B ).

Second to fourth abdominal somites with four spines on anterior ridge, with some transverse striae and scales. Posterior ridge of fourth abdominal somite bears median spine.

Eyes large: maximum corneal diameter 0.3 times the distance between the bases of the anterolateral spines.

Basal segments of antennule (distal spines excluded) about 0.3 times the carapace length, elongate, overreaching corneae, with two distal spines, mesial spine clearly shorter than lateral spine; with two spines on lateral margin, proximal spine short, distal spine moderately long ( Fig. 1C ). First segment of antennal peduncle with stout process on mesial margin reaching end of second segment; second to fourth segments unarmed ( Fig. 1C ).

With Mxp 3 ischium about twice the length of the merus, measured along the dorsal margin, and distoventrally bearing a long spine. Merus with one well-developed median spine on flexor margin; extensor margin with small distal spine ( Fig. 1D ).

With P1s subequal in length, squamous, with some uniramous and plumose setae, and with some iridescent setae on mesial borders of merus and carpus, about five times the carapace length; merus clearly longer than carapace length, carpus four times longer than high, and 0.7 times palm length; palm nearly nine times longer than high, and 1.4 times longer than fingers. Merus armed with row of spines on mesial, ventral, and dorsal borders. Carpus and palm with row of spines on mesial margin, a few small spines on dorsal side. Fingers unarmed, with longitudinal carina on each side, distally curving and crossing, and ending in a sharp point (fixed finger of right cheliped in holotype regenerating) ( Fig. 1E ).

With P2 about three times the carapace length; merus nearly 1.5 times longer than carapace, between nine and ten times as long as high, 4.0–4.5 times the carpus length, and 1.3–1.5 times as long as propodus; propodus ten times as long as high, and nearly twice the dactylus length ( Fig. 1F ); end of propodus reaching or slightly overreaching end of P1 merus. Merus with spines along dorsal border, increasing in size distally, a few small spines along distal part of ventral margin, with distal spine strong. Carpus with strong distomesial and distoventral spine. Propodus with row of minute movable small ventral spinules (not discernible in Fig. 1F ). Dactylus slightly curving distally, ventral margin slightly curving with 26– 28 movable small spinules, distal third unarmed ( Fig. 1F, G ). Length, armature, and article proportions of P3 and P4 similar to those of P2.

Remarks: The new species closely resembles Agononida prolixa (Alcock, 1894) from the Arabian Sea, Sri Lanka, and the Andaman Sea ( Ahyong & Poore, 2004; Baba, 2005). In both species, supraocular spines fall short of the rostral tip, the carapace has three branchial lateral spines, protogastric spines are absent, the fourth abdominal segment has one spine on the posterior transverse ridge, and the basal article of the antennal peduncle bears a moderately sized process, not overreaching the fourth article.

The two species may be distinguished as follows.

1. The posterior margin of the carapace is armed with two median spines in A. prolixa , whereas these spines are absent in the new species.

2. The distomesial angle of the second article of the antennal peduncle is armed with a spine in A. prolixa . In A. isabelensis sp. nov., this angle is unarmed.

The new species is also close to Agononida similis ( Baba, 1988) from the Philippines and Indonesia ( Baba, 1988). However, they can be differentiated according to the number of spines along the branchial margin of the carapace: four in A. similis and three in A. isabelensis sp. nov. Furthermore, the lateral margin of the basal article of the antennular peduncle has two well-developed spines in the new species, whereas this margin has only one spine in A. similis .

Distribution: Solomon Islands, at a depth of between 240 and 347 m.

Figures

Figure 1. Agononida isabelensis sp. nov. male holotype, 20.7 mm (MNHN-Ga 6496), Solomon Islands. A, carapace and abdomen, dorsal view. B, sternum. C, left antennule and antenna, ventral view. D, ischium and merus of right third maxilliped, lateral view. E, right cheliped, lateral view. F, right P2, lateral view. G, dactylus, right P2, lateral view. Scale: A, B, E, F = 5 mm; C, D, G = 2 mm.