Gastroptychus spinirostris, Ahyong & Poore, 2004

Ahyong, Shane T. & Poore, Gary C. B., 2004, The Chirostylidae of southern Australia (Crustacea: Decapoda: Anomura), Zootaxa 436 (1), pp. 1-88 : 9-11

Gastroptychus spinirostris n. sp. ( Fig. 1 )

Type material. HOLOTYPE: AM P31418, 1 male (7.3mm), NE of Tweed Heads , Queensland, 28º02–05’S, 153º57’E, 364 m, trawl, K78­09­03, 1 Jun 1978 . PARATYPES: AM P31417, 2 females (7.9–11.7 mm), type locality .

Diagnosis. Rostrum with lateral spines Dorsal surface of carapace with evenly distributed, slender, upright spines, largest laterally and anteriorly; surface non­setose. Sternite 3 with narrow median sinus flanked by small spine; lateral margins with small spine.. Abdominal somites covered with slender, upright spines, largest on first 3 somites; sparsely setose.

Description. Carapace: Rostrum about three­quarters remaining carapace length, with pair of anteriorly directed spines basally and at proximal third or half; sparsely setose on distal half. Outer orbital angle with small spine. Dorsal surface with evenly distributed slender, upright spines, largest laterally and anteriorly; surface non­setose; pterygostomian region with several small spines.

Sternum: Sternite 3 (that of maxilliped 3) with narrow median sinus flanked by small spine; lateral margins with small spine. Lateral margin of sternite 4 (that of pereopod 1) with small distal and large proximal spine; with median pair of anteriorly directed spines. Sternite 5 (that of pereopod 2) with large lateral spine.

Abdomen: Somites covered with slender, upright spines, largest on first 3 somites; sparsely setose; pleura tapering to angular apex. First somite with transverse row of 4 spines. Second to sixth somites with 2 transverse rows of spines. Second somite with anterior row of 4–6 spines and posterior row of 6–8 spines. Third somite with anterior row of 4 spines and posterior row of 8 spines. Fourth somite with anterior row of 4 spines and posterior row of 6 spines. Fifth somite with anterior row of 4 spines and posterior row of 6 spines. Sixth somite with anterior row of 6 spines and posterior row of 4 spines; with small posterolateral point and 4 denticles on posterior margin. Telson comprising 2 articulating plates; proximal plate shorter and wider than distal, rounded laterally; distal plate half as long as wide, posteriorly emarginate, rounded laterally. Uropodal endopod and exopod ovate.

Eyes: Cornea subglobular, slightly wider than peduncle, reaching anteriorly almost to midlength of rostrum.

Antennule: Basal segment with small mesiodistal spine and two larger spines on laterodistal margin; peduncle not reaching rostral apex.

Antenna: Basal segment with strong lateral spine. Peduncle second segment with 2 small distal spines; penultimate segment with ventrodistal spine; ultimate segment with distal and midventral spine. Scaphocerite lanceolate, extending beyond second segment of peduncle.

Maxilliped 3: Basis with stout distal flexor spine. Endopod ischium with 2 distal spines, of which one located on crista dentata; merus and carpus with several stout spines; dactylus about half propodus length, both unarmed.

Pereopod 1 (cheliped): Subcylindrical, about 2.5 times carapace length; with few scattered setae and numerous slender anteriorly inclined spines. Propodus longer than carpus; palm about three times as long as high; pollex spinose ventrally; occlusal margin dentate. Dactylus shorter than palm; spinose dorsally; occlusal margin dentate.

Pereopods 2–4: Similar, flattened, about 1.5 times carapace length; sparsely setose. Basis spinose. Ischium, carpus and merus strongly spinose on extensor and flexor margins, with smaller spines on lateral surface. Propodus with extensor margins lined with slender fixed spines, flexor margins lined with slender movable spines. Dactylus about 0.6 propodus length, with 9–11 fixed spines on flexor margin.

Etymology. The specific epithet is derived from the Latin spina, meaning ‘thorn’, and rostrum, meaning ‘nose’, alluding to the spinose rostrum of this species.

Remarks. Gastroptychus spinirostris n. sp. is unique in the genus for bearing 2 pairs of lateral spines on the rostrum. In the general pattern of dorsal spination, large eyes, and carapace proportions, G. spinirostris most closely resembles G. ciliatus ( Van Dam, 1933) from Indonesia. Aside from the possession of lateral rostral spines, G. spinirostris differs from G. ciliatus in having two instead of one transverse row of spines on the second to fifth abdominal tergites, markedly fewer spines on chela, a relatively shorter propodal palm on the cheliped (about 1.5 times dactyl length vs. about 3 times dactyl length), and a transverse row two instead of six spines on the surface of the sternum.

Gastroptychus spinirostris resembles G. ciliatus and G. chacei Baba, 1986 , and differs from other congeners in having a distinctly concave instead of transverse or convex anterior margin of the sternal plastron, and in bearing a broadened instead of very slender, spiniform rostrum. In these characters, G. spinirostris , G. ciliatus and G. chacei resemble species Uroptychus . The three species, however, agree with Baba’s (1988) concept of Gastroptychus in having distinctly spinose walking legs and are retained in the genus pending revisionary studies by K. Baba.

Distribution. Known only from northeast of Tweed Heads, southern Queensland, at 364 m depth.

Figures

FIGURE 1. Gastroptychus spinirostris n. sp., male holotype, 7.3 mm, AM P31418. A, dorsum. B, right lateral. C, abdomen, dorsal. D, sternum. E, maxilliped 3, right lateral. F, antennal peduncle, left ventral. G, basal antennular segment, left ventral. Scale A–D = 2 mm, E–G = 1 mm.