Trierarchus squamosus

Shaga, I Bevin, Priya, K, Ramar, Selvakumar, Srinidhi, S, Mohan, G Chandra, Ranganathan, Sukanya, Moulvi, S M M & Mani, Bhuvaneswari, 2023, A Small Collection of Subtidal Crabs (Crustacea: Decapoda: Brachyura) from the Palau Islands Collected by Dredging, Bulletin of the National Museum of Nature and Science. Series A, Zoology 49 (1), pp. 7-42 : 22

Trierarchus squamosus

( Stephenson and Hudson, 1957)

( Figs. 8, 10A, 15F–G)

Thalamita squamosa Stephenson and Hudson, 1957 , pp. 320 (in key), 355, figs. 2K, 3K, pl. 5 fig. 4, pl. 8 fig. Q, pl. 10 fig. J. ʕ Stephenson, 1976, p. 24. Trierarchus squamosus (Stephenson and Hudson) : Evans, 2018, p. 14 (in table), fig. 3J.

Material examined. Entrance to Toagel Mid in Arangel Channel, Babelthuap I., Palau Is., dredged, 30–40 m in depth, with coralline algae; 1 Ə (cb 12.6×cl 8.7 mm), NSMT-Cr 30977; June 19 1980; K. Baba leg.

Remarks. This species is most characteristic in having only four strong and sharp anterolateral teeth of the carapace including the external orbital tooth ( Figs. 8A, 10A); posterior three teeth are only slightly smaller than the first or the external orbital tooth. All the ridges of the carapace areolae are distinct ( Figs. 8A, 10A). The frontal margin is cut into four lobes ( Figs. 8A, 10A); each median lobe about two-thirds as wide as the lateral lobe, its outer end being shortly overlapped by the lateral lobe; the lateral lobe is slightly behind the frontal level of the median lobe, weakly concave in the middle, making the appearance of the six-lobed front. The frontal and supraorbital margins are narrowly crested along the whole lengths ( Fig. 10A). The antennal basal segment is armed with a distinct ridge tipped with small granules along the distal half. The third maxilliped is as figured, with the anterodistal angle of the merus is narrowly extended forward ( Fig. 15F). The male pleon is comparatively wide, with the bulged sixth pleonite ( Fig. 8B). Both chelipeds are somewhat different in size and shape ( Fig. 8C–D); the surfaces of the carpus and palm are of somewhat squamous appearance with depressed granules of variable sizes; the fingers are strongly and irregu- larly toothed throughout the lengths of both cutting edges. The G1 was roughly figured by Ste- phenson and Hudson (1957: fig. 2K) and in the present paper ( Fig. 15G); the shaft is stout, parallel-sided throughout the length, strongly curved at the middle.

Distribution. The Great Barrier Reef; Rongelap and Bikini Atolls in the Marshall Islands, 45–55 m in depth. New to the Palau Islands.