Uroptychus insignis

Uroptychus insignis (Henderson, 1885)

(Fig. 5)

Diptychus insignis Henderson, 1885: 419 (type locality: off Marion Island, Prince Edward Islands, 46°41'S, 38°10'E, 567 m). Uroptychus insignis.— Henderson, 1888: 175, pl. 21, figs 1, 1a, 1c [not 1b].— Baba, 2005: 227 (key, synonymies).— Baba et al., 2008: 34 (synonymies).— Ahyong et al., 2015: 111, figs. 3, 4 (part).

Type material. BMNH 1902.10.2.9–14, ov. female lectotype (cl 17.1, pcl 10.6 mm), 6 male paralectotypes (pcl 4.5–10.7 mm), 7 female paralectotypes (pcl 3.1–11.0 mm), off Marion Island, Prince Edward Islands, southern Indian Ocean, 46°41'S, 38°10'E, 567 m, “Challenger” Stn. 145A.

Material examined. AM P97998, 1 female (cl 14.3, pcl 9.0 mm), Kerguelen Islands, 50°06'S, 64°48'E, 489 m, 22 September 2010, Poker II st. 180.

Diagnosis. Carapace excluding rostrum wider than long; dorsum smooth, densely setose on chelipeds and carapace, with transverse row of small epigastric spines; lateral margins divergent, spinose; anterolateral spine overreaching outer orbital spine; anterior branchial spine separated from remaining branchial spines by wide unarmed margin (occasionally with 1 or 2 small spines). Rostrum sharply triangular, margins unarmed or with few minute denticles. Sternite 3 anterior margin with deep, V-shaped median emargination. Basal antennal article with small outer spine; ultimate and penultimate articles each with distal spine. Antennal scale extending almost to or slightly overreaching apex of ultimate peduncle article. Ocular peduncle 1.4–1.5 × as long as wide. Crista dentata uniformly and minutely dentate. P2–4 similar; merus with small spines on extensor margin; propodus flexor margin broadened distally and lined with movable spines; dactylus flexor margin lined with strong, obliquely directed, corneous teeth.

Remarks. The known distribution of Uroptychus insignis (Henderson, 1885) now remains in the southwestern Indian Ocean (Prince Edward Island, Crozet, Kerguelen and Amsterdam islands, Fig. 1). Ahyong et al. (2015) note no significant morphological differences between specimens from these locations other than allometric differences in cheliped size and spination. Uroptychus insignis and U. macquariae n.sp. are clearly very closely allied. Despite subtle (but consistent) morphological differences between the Macquarie and the Kerguelen Islands forms, they clearly differ genetically with more than 7% sequence divergence, indicating prolonged isolation. Any future attempts to identify new material will likely need to take into account the locality of the collections, particularly if the specimens are small.

Both Uroptychus insignis and U. macquariae n. sp. most closely resemble U. zeidleri Ahyong & Poore, 2004, from Tasmania (520 m) and U. spinulosus Dong & Li, 2015 from a cold seep SW of Taiwan (1121 m). Uroptychus macquariae n. sp. can be separated from U. zeidleri by the branchial marginal carapace spination, arranged in a single, even, unbroken row in U. zeidleri, while in U. insignis and U. macquariae n.sp., the anterior branchial spine is separated from the remainder by an unarmed interval, or at most with 1 or 2 small, well-spaced spines. Additionally, the dentition of the crista dentata differs (teeth evenly decreasing in size distally in U. zeidleri; teeth uniformly minute in U. insignis and U. macquariae n.sp.). The only known specimen of U. spinulosus is smaller (pcl 3.7 mm) than both Uroptychus insignis and U. macquariae n.sp., which makes comparisons difficult. The holotype of U. spinulosus has an unarmed second article of the antennal peduncle, while it is armed with a lateral spine in both U. insignis and U. macquariae. The cheliped merus is armed with one single large spine along the mesial margin in U. spinulosus, and the lateral hepatic carapace region is unarmed (while it bears 1–2 small spines even in small specimens of both U. insignis and U. macquariae).

Distribution. Southwestern Indian Ocean off Prince Edward Island, Amsterdam Island, the Crozet and Kerguelen Islands; 315–1680 m.