Uroptychus nigricapillis Alcock, 1901

Ahyong, Shane T. & Baba, Keiji, 2004, Chirostylidae from north-western Australia (Crustacea: Decapoda: Anomura), Memoirs of Museum Victoria 61 (1), pp. 57-64 : 60-62

Uroptychus nigricapillis Alcock, 1901

Figures 2A–I

Uroptychus nigricapillis Alcock, 1901: 282–284 , pl. 3 fig. 3, 3a [type locality: Andaman Islands].— Alcock and McArdle, 1902, pl. 56 fig. 3.

Material examined. AM P67832 , 1 ovigerous female (11.0 mm), North West Shelf , 240 km NW of Port Hedland, Western Australia, 500 m, J. Paxton, 7 Apr 1982 (stn S02/82/31) .

Diagnosis. Carapace excluding rostrum distinctly longer than broad; lateral margins slightly divergent; with 3 or 4 small spines behind base of cervical groove; with anteriorly directed anterolateral spine; posterior quarter with low ridge. Rostrum sharply triangular, exceeding one-third length of remaining carapace. Outer orbital angle produced to small spine extending to level of anterolateral spines. Dorsum with pair of distinct epigastric spines. Sternite 3 anterior margin deeply emarginate, with pair of median spines separated by narrow notch. Antennal basal segment with small outer spine; ultimate and penultimate segments unarmed. Antennal scale extending slightly beyond midlength of ultimate peduncular segment. Chelipeds smooth, fingers setose. Pereopod 4 slightly shorter than pereopods 2 and 3; sparsely setose; propodi with 6–9 movable spines on distal flexor margin, none paired; distalmost flexor spine remote from distal margin; dactyli with 8–10 small spines on flexor margin, oriented oblique to dactylar margin, distal 2 appressed.

Description. Carapace: Length excluding rostrum distinctly greater than breadth. Lateral margins slightly divergent; with 3 or 4 small spines behind base of cervical groove, anteriormost spine with small additional dorsal spine; with anteriorly directed anterolateral spine; posterior quarter with low carina. Rostrum sharply triangular, exceeding one-third length of remaining carapace; margins unarmed. Outer orbital angle produced to small spine extending to level of anterolateral spines. Dorsum smooth, with pair of distinct epigastric spines; cervical groove distinct medially. Pterygostomian flap with small anterior spine.

Sternum: Plastron broader than long, widening posteriorly. Sternite 3 (at base of maxilliped 3) depressed, anterior margin narrow, deeply emarginate, with pair of median spines separated by narrow notch; with distinct anterolateral tooth. Sternite 4 (at base of pereopod 1) with distinct anterolateral tooth extending anteriorly to level of base of emargination of sternite 3; margins dentate, irregular; demarcation between sternites 4 and 5 dentate.

Abdomen: Abdominal segments glabrous. Telson length about half breadth; distal portion posteriorly emarginate, about twice length of proximal portion.

Eye: Cornea moderately dilated, subequal to length of peduncle; reaching to distal quarter of rostrum;

Antenna: Basal segment with small outer spine. Peduncle extending to distal third of rostrum. Flagellum about 3 times as long as peduncle. Ultimate and penultimate segments unarmed; ultimate segment about 2.5 times length of penultimate segment. Antennal scale slightly wider than opposite peduncular segments, extending slightly beyond midlength of ultimate peduncular segment.

Maxilliped 3: Dactylus, propodus, carpus and merus unarmed. Crista dentata distinctly serrate on proximal two-thirds of ischium, extending onto basis.

Pereopod 1 (cheliped): Slender, cylindrical, about 3.5 times carapace length; glabrous dorsally; fingers setose. Palm about 4 times as long as high, about 1.5 times as long as fixed finger; lower margin with row of low granules. Fingers crossing, opposable margins dentate; occlusal margin of movable finger with obtuse process proximally; occlusal margin of fixed finger without distinct prominence. Carpus longer than merus and propodal palm; glabrous. Merus usually with several low granules on inner proximal margin. Ischium with short, slender spine on dorsolateral margin.

Pereopods 2–4 (walking legs): Similar; sparsely setose; decreasing in length posteriorly. Pereopod 1 merus longer than carapace. Merus extensor margin smooth. Carpus about 0.5 merus length, about two-thirds propodus length. Propodi not broadened distally, with 6–9 movable spines on distal flexor margin; distalmost flexor spine remote from distal margin. Dactyli setose marginally, with 8–10 small spines on flexor margin, oriented oblique to dactylar margin, distal 2 appressed. Pereopod 4 slightly shorter than pereopods 2 and 3.

Ova : Diameter 0.8 mm.

Remarks. The single Australian specimen agrees well with the original account and figures of U. nigricapillis in most respects ( Alcock, 1901; Alcock and McArdle, 1902) and represents the first record from Australian waters. It differs from figures of the holotype in having relatively longer legs, such that the merus of the first walking leg in the Australian specimen is longer than, instead of shorter than, the carapace length (excluding rostrum). In a series of Indian Ocean specimens (from several localities) attributed to U. nigricapillis, Tirmizi (1964) noted considerable variation in the ornamentation of the sternites, the distinctness of the epigastric and lateral spines on the carapace, and length of the antennal scale – features normally considered diagnostic in many species. Unfortunately, the sternum of the holotype of U. nigricapillis was neither figured nor described by Alcock (1901). A Java Sea specimen figured by Van Dam (1940: fig. 2), however, bears a transverse row of tubercles behind the dentate anterior margin of sternite 4 in contrast to the Australian specimen which lacks tubercles. Tirmizi (1964) also noted variation in the sternal armature, in which the sternum of only one specimen resembled Van Dam’s (1940) figure. The Australian specimen bears well-developed epigastric spines, and small but distinct lateral carapace spines as in Alcock’s (1901) account. Variation in the presence and degree of epigastric ornamentation is also known in other congeners (e.g. U. australis ( Henderson, 1885) , U. gracilimanus ( Henderson, 1885) , U. vandamae Baba, 1990 ). However, variation in other characters mentioned by Tirmizi (1964) and other studies (e.g. Baba, 1981, 1988), namely, the lateral carapace spination and ornamentation and morphology of the sternal plastron, suggests that more than one species could be confused under U. nigricapillis . In view of morphological variation in U. nigricapillis reported in previous studies, the Australian specimen is described and illustrated.

Uroptychus nigricapillis closely resembles U. gracilimanus , described from off Port Jackson, in general habitus, armature of the dactyli of the walking legs, and in variation in the presence and size of the epigastric spines. Uroptychus nigricapillis differs, however, in the presence of lateral spines on the carapace margins, in bearing a short slender spine instead of a low tooth on the cheliped ischium, and in the spination of the propodi of the walking legs. Thus, in U. nigricapillis and the distal flexor spine on the propodi of the walking legs is positioned more remotely from the distal margin than in U. gracilimanus ( Fig. 2A ). The distal-most of the flexor spines is located close to the articul-ation with the dactylus, a fact confirmed by examination of the holotype of U. gracilimanus ( BMNH 1888: 33, off Port Jackson). In the specimen of U. gracilimanus figured by Ahyong and Poore (2004: fig. 10, AM P65825, off Port Jackson), some of the movable propodal spines on the walking legs are damaged or lost. The dactylus and distal portion of the propodus of the left first walking leg of the same specimen of U. gracilimanus is shown ( Fig. 2J ) for comparison with the condition in U. nigricapillis .

Distribution. Western Indian Ocean, Andaman Sea, Indonesia, the Philippines and now from north-western Australia at 66–1930 m depth.

Figures

Figure 2. A–I, Uroptychus nigricapillis Alcock, 1901, ovigerous female (11.0 mm), AM P67832. J, Uroptychus gracilimanus (Henderson, 1885), female (9.4 mm), AM P65825. A, dorsum. B, carapace, right lateral view. C, cheliped, proximal ventral view. D, cheliped, distal ventral view. E, right antenna, ventral view. F, right maxilliped 3, lateral view. G, crista dentata, right. H, sternal plastron. I, telson. J, left pereopod 2, dactylus and distal propodus. Scale A–D = 3.0 mm, E–F = 0.7 mm, G–J = 1.5 mm.