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. ─ 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 ♂ (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 irregularly toothed throughout the lengths of both cutting edges. The G1 was roughly figured by Stephenson 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.