Uroptychus joloensis Van Dam, 1939

Ahyong, Shane T. & Baba, Keiji, 2004, Chirostylidae from north-western Australia (Crustacea: Decapoda: Anomura), Memoirs of Museum Victoria 61 (1), pp. 57-64 : 58-60

Uroptychus joloensis Van Dam, 1939

Figure 1

Uroptychus joloensis Van Dam, 1939: 395–398 , figs 2, 2a, 2b, 2c

[ type locality: Jolo , Indonesia] .

Material examined. NMV J21046 , 2 males (5.6–7.3 mm), ovigerous female (7.8 mm), North West Shelf between Port Hedland and Dampier, 18°45'S, 118°24'E, 142 m, trawl, G. Poore and H. Lew Ton, 5 Jun 1983 (stn NWA-23) .

Diagnosis. Carapace lateral margins convex; dorsum unarmed; with anteriorly directed anterolateral spine and 2 lateral spines in advance of midlength; with low, narrow, marginal ridge extending from orbital to posterior margin. Sternal plastron with faintly concave anterior margin, and median notch. Cornea not dilated, about one-third length of remaining stalk. Antennal basal segment with small lateral spine; ultimate and penultimate segments of peduncle each with long distal spine. Antennal scale not exceeding apex of ultimate peduncle segment. Chelipeds smooth but sparsely setose; ischium with 2 dorsal and 1 ventral spine. Walking legs similar, slightly decreasing in length posteriorly, sparsely setose, segments smooth; propodus with paired movable spines on distal flexor margin; dactylus with 6 or 7 strong, widely spaced, perpendicularly (or near perpendicularly) directed corneous teeth on flexor margin.

Description. Carapace: Length excluding rostrum slightly less than breadth. Lateral margins convex; with anteriorly directed anterolateral spine and 2 lateral spines in advance of midlength; with low, narrow, marginal ridge extending from orbital to posterior margin. Rostrum narrow, triangular, dorsally excavate. Outer orbital angle produced to small acute spine. Dorsum smooth, with scattered setae. Pterygostomian flap visible in dorsal view; with strong anterior spine, otherwise unarmed.

Sternum: Plastron about as long as wide, subquadrate. Sternite 3 (at base of maxilliped 3) with faintly concave or irregular anterior margin; with narrow, U-shaped median notch; anterolateral angle with blunt tubercle; anterior margin level with or very slightly exceeding sternite 4. Sternite 4 (at base of pereopod 1) with anterolateral margins angular.

Abdomen: Segments smooth, sparsely setose. Telson about one-third as long as broad; distal portion broadly convex posteriorly, shorter than proximal portion.

Eye: Cornea not dilated, about one-third length of remaining stalk; reaching approximately to midlength of rostrum.

Antenna: Basal segment with distolateral spine. Peduncle extending almost to apex of rostrum. Ultimate segment longer than penultimate segment, both with long distomesial spine. Antennal scale slightly wider than opposite peduncular segments, extending almost to apex of ultimate segment (excluding distal spine).

Maxilliped 3: Dactylus and propodus unarmed. Carpus with proximal spine on extensor margin. Merus with distalolateral spine and 2 small flexor spines. Ischium with small distal spine lateral to rounded flexor distal margin. Crista dentata denticulate for length of ischium.

Pereopod 1 (cheliped): About 4 times carapace length; smooth but sparsely setose. Palm 5 times as long as high. Fingers crossing, opposable margins dentate and each with low process proximally; slightly longer than one-third palm-length. Carpus about as long as palm. Merus with 2 or 3 small spines on lower proximal margin. Ischium with 2 dorsal spines; ventrally with short subterminal spine on mesial margin.

Pereopods 2–4 (walking legs): Similar, slightly decreasing in length posteriorly, sparsely setose; segments smooth. Merus shorter than carapace. Propodus more than twice as long as carpus, not broadened distally, with paired movable spines on distal flexor margin. Dactylus with 6 or 7 strong, widely spaced, perpendicularly (or near perpendicularly) directed corneous teeth on flexor margin.

Remarks. The present specimens generally agree with the type account of U. joloensis Van Dam, 1939 , based on a specimen from Jolo, Indonesia, in carapace shape and lateral spination, the armature of the dactyli of the walking legs, and small eyes. The present specimens differ from the type account of U. joloensis chiefly in the following features: the rostrum lacks distalolateral spines, the fingers of the cheliped are longer than one-third instead of about one-quarter the length of the propodal palm, the anterior margin of the sternal plastron (sternite 3) does not distinctly exceed that of sternite 4, and the median notch of the sternal plastron is distinctly narrowed rather than a broad U-shape. The difference in rostral spination, whether apically trifid (as in the type) or singular (as in present material) is variable in this species as also in U. tridentatus ( Henderson, 1885) and U. zezuensis Kim, 1972 (Baba, unpublished). The last mentioned differences appear to be within the range of expected morphological variation. As only the second record of the species, a description and figures of Australian material are provided.

Distribution. Jolo, Indonesia, and now from north-western Australia at depths between 37.8–56.7 m and 142 m.

Figures

Figure 1. Uroptychus joloensis Van Dam, 1939, ovigerous female (7.8 mm), NMV J21046. A, dorsum. B, anterior carapace, right lateral view. C, right cheliped, proximal mesial view. D, right antenna, ventral view. E, right maxilliped 3, lateral view. F, crista dentata, right. G, sternal plastron. H, telson. Scale A–C, G = 3.0 mm, D–F = 0.7 mm, H = 1.5 mm.