Uroptychus oxymerus, Ahyong & Baba, 2004

Ahyong, Shane T. & Baba, Keiji, 2004, Chirostylidae from north-western Australia (Crustacea: Decapoda: Anomura), Memoirs of Museum Victoria 61 (1), pp. 57-64 : 62-64

Uroptychus oxymerus sp. nov.

Figure 3

Material examined. Holotype: NMV J21040 , male (> 6.5 mm), North West Shelf , between Port Hedland and Dampier, 184 m, G. Poore and H. Lew Ton, 6 Jun 1983 (stn NWA-24).

Diagnosis. Carapace lateral margins convex; dorsum unarmed; with strong, anteriorly directed anterolateral spine and 5 or 6 stout lateral spines. Rostrum apically trifid; dorsally excavate. Sternal plastron with faintly concave anterior margin, and median notch. Cornea not dilated, about one-third length of remaining stalk. Antennal basal segment with outer spine; ultimate and penultimate segments of peduncle each with long distal spine. Antennal scale exceeding apex of ultimate peduncle segment. Chelipeds rugose, setose; merus with row of strong, stout spines on mesial ventral margin. Walking legs similar, slightly decreasing in length posteriorly, setose, segments rugose; propodus distal flexor margin with 2 or 3 movable spines, distal most paired; dactylus with 6 or 7 strong, widely spaced, perpendicularly (or near perpendicularly) directed corneous teeth on flexor margin.

Description. Carapace: Length excluding rostrum subequal to breadth. Lateral margins convex; with anterolateral spine and 5 lateral spines and spinule above third lateral spine; anterolateral spine, strong, directed anteriorly; first and second lateral spine slender; third and fourth lateral spines stout, larg- er than others; fifth lateral spine low, blunt. Rostrum apically trifid; dorsally excavate. Outer orbital angle produced to small acute spine. Dorsum smooth, with scattered setae. Pterygostomian flap with strong anterior spine and field of spines and tubercles on anterior half.

Sternum: Plastron about as long as wide, subquadrate. Sternite 3 (at base of maxilliped 3) anterior margin shallowly concave, with narrow U-shaped median notch, anterolateral angle blunt. Sternite 4 (at base of pereopod 1) with anterolateral margins pointed, not produced beyond anterior concavity of sternite 3.

Abdomen: Segments glabrous. Telson about half as long as broad; distal portion posteriorly emarginate, longer than proximal portion.

Eye: Cornea not dilated, about half as long remaining stalk; not reaching beyond midlength of rostrum;

Antenna: Basal segment with distolateral spine. Peduncle extending beyond distal half of rostrum. Ultimate segment about twice as long as penultimate segment, both with long distomesial spine; ultimate also with 2 small marginal spines. Antennal scale slightly wider than opposite peduncular segments, extending slightly beyond apex of ultimate segment.

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

Pereopod 1 (cheliped): About 4 times carapace length; all segments rugose and setose. Palm 3 times as long as high, about 2.5 times as long as fixed finger; surface with short, transverse, depressions. Fingers crossing, opposable margins dentate and each with low process proximally. Carpus with small lower distal spine adjacent to each articular condyle of propodus. Merus with row of 5 stout spines on mesial ventral margin and group of 3 spines proximally. Ischium with 2 dorsal spines and 1 ventral spine; distal dorsal spine slender, depressed.

Pereopods 2–4: Similar, slightly decreasing in length posteriorly, strongly setose; segments rugose, setose. Merus shorter than carapace. Propodus more than twice length of carpus, not broadened distally, with 2 or 3 movable spines on distal flexor margin, distalmost paired. Dactylus with 6 or 7 strong, widely spaced, perpendicularly (or near perpendicularly) directed corneous teeth on flexor margin.

Etymology. From oxy, sharp, and merus, the fourth limb segment, in reference to the sharp, stout spines on the merus of the cheliped that distinguish the new species from U. tridentatus and U. zezuensis .

Remarks. Uroptychus oxymerus sp. nov. closely resembles U. tridentatus ( Henderson, 1885) , described from Indonesia, and U. zezuensis Kim, 1972 from Korea, in almost all respects including the spinose carapace margins, distally spinose segments of the antennal peduncle, armature of pereopods 2–4, and shape of the sternal plastron. The new species is readily distinguished from both U. tridentatus and U. zezuensis by having a row of large, stout spines instead of a cluster of spines on the mesial ventral margin of the merus of the cheliped, in having three instead of two spines on the extensor margin of the carpus of the third maxilliped, and in having spines along the lower margin of the ultimate segment of the antennal peduncle in addition to the distal spine.

Four species of Uroptychus are now known from the North West Shelf. Uroptychus oxymerus is readily distinguished from U. joloensis by having distinctly more spinose lateral carapace margins (5 or 6 instead of 2); from U. nigricapillis by lacking a pair of epigastric spines on the carapace and in having a distal spine on the ultimate and penultimate segments of the antennal peduncle; and from U. brucei by having lateral carapace spines.

Distribution. Known only from the type locality at 184 m depth.

Figures

Figure 3. Uroptychus oxymerus sp. nov., holotype male (+6.5 mm), NMV J21046. A, dorsum. B, carapace, right lateral view. C, right cheliped, proximal mesial view. D, left antenna, ventral view. E, right maxilliped 3, lateral view. F, crista dentata, right. G, sternal plastron. H, telson. Scale A–C = 2.0 mm, D–H = 1.0 mm.