Trierarchus squamosus ( Stephenson and Hudson, 1957 )

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. ─ 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.

Figures

Fig. 8. Trierarchus squamosus (Stehenson and Hudson 1957), ♂ (NSMT-Cr 30977; cb 12.6×cl 8.7mm). Carapace in dorsal view (A), abdomen (B), both chelipeds in outer (C) and upper (D) views.

Fig. 10. A: Trierarchus squamosus (Stephenson and Hudson, 1957), ♂ (NSMT-Cr 30977; cb 12.6×cl 8.7mm). Front-orbital region in dorsal view. B–C: Chlorodiella xishaensis Chen and Lan, ♂ (NSMT-Cr 30983; cb 8.0×cl 5.7mm). Left G1 in ventral view (B) and right third ambulatory leg in dorsal view (C). D–F: Chlorodiella corallicola Miyake and Takeda, ♂ (holotype, ZLKU 1724; cb 6.6×cl 4.4mm). Distal part of right G1 in ventral (D) and sternal (E) views (original figures by Miyake and Takeda, 1968). Scales for A=5mm, B= 0.5mm, C=3 mm, F=0.5 mm.

Fig. 15. A–B: Palicoides whitei (Miers), ♂(NSMT-Cr 31000; cb 7.0×cl 4.7mm). Left orbital region, with third maxilliped, in ventral view (A) and right G1 in sternal view (B). Arrow in Fig. A shows a curved tubercle extending from the eyestalk to guard the cornea. C–E: Neopalicus jukesii (White), ♂ (NSMT-Cr 30997; cb 8.2×cl 7.3mm). Left third maxilliped (C), G1 in ventral view (D) and distal part of the same in sternal view (E). F–G: Trierarchus squamosus (Stephenson and Hudson, 1957), ♂ (NSMT-Cr 30977; cb 12.6×cl 8.7mm). Left third maxilliped (F) and left G1 in sternal view. (G). Scales for AC=1mm, BEFG=2 mm, D=0.5mm.