Notonyx aff. sagittifer Ng and Clark, 2010

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 : 28

Notonyx aff. sagittifer Ng and Clark, 2010

( Fig. 11C–E )

Notonyx nitidus A. Milne Edwards : Serène and Umali, 1972, p. 82, figs. 90–95, pl. 8 figs. 9–10.─ Serène and Soh, 1976, fig. 16E.

Notonyx sagittifer Ng and Clark, 2010, p. 31 , figs. 1–3.

Material examined. Entrance to Toagel Mid in Arangel Channel, Babelthuap I., Palau Is., dredged, 40–50 m depth, mud; 1♂ (cb 5.0×cl 3.3 mm), NSMT-Cr. 30991; June 19, 1980; K. Baba leg.

Remarks. The smooth, transversely quadrangular carapace of the male shows without doubt its suitable taxonomic position in the genus Notonyx . All of the known 12 species are small in size, less than cb 10 mm, and closely resemble to each other in the carapace, chelipeds and ambulatory legs. Their general morphological differences are sometimes subtle, but based on close observation, there may be constant differences in the shape of the carapaces, and the G1 shape is the most important character to distinguish each species. Ten species described intensively during recent some years by Clark and Ng (2006, 2011), Ng and Clark (2008, 2010), Naruse and Maenosono (2009), Naruse and Takeda (2010), Rahayu and Ng (2010a, b), and Rahayu (2011) are mostly well described with the figures and photographs, but the status of the type species, N. nitidus A. Milne-Edwards, 1873 , from New Caledonia still remains unclear.

Quite unfortunately, the male specimen examined lacks the pleon together with the G1, and also all the ambulatory legs are absent in a specimen vial. The general shape of the carapace seems to be close to N. sagittifer Ng and Clark (2010) from Mindanao, the Philippines, which was compared with N. latus Ng and Clark, 2008 , from the Lesser Sunda Islands. The holotype specimen of N. sagittifer is a male previously identified as N. nitidus by Serène and Umali (1972). The general shape of the carapace ( Fig. 11C ) seems to be closer to N. sagittifer rather than the other congeneric species, but the identification of the specimen at hand is not always definitive because of lacking the male G1. The ratio of the carapace breadth to length is 1.28, and the carapace anterolateral margin is only weakly convex outwards. Both chelipeds are compressed in dorsal view ( Fig. 11E ) and each palm is wholly glabrous, with the keeled lower margin ( Fig. 11D ). The male G1 is needed for the definite identification.

Distribution. The Notonyx species are reported from the limited localities, probably due to the special habitat in shallow water grass bed with sand and gravel substrates. As mentioned by Rahayu (2011), four species are exclusively known from Indonesian waters; two species from the Philippines; each one species from the Andamans, Thailand, Fiji, New Caledonia and Japan; only N. kumi Naruse and Maenosono, 2009 , has been reported from the distant localities, the Ryukyu Islands in Japan and the Lesser Sunda Islands in Indonesia. The present record of the genus is new to Micronesian waters.

Figures

Fig. 11. A–B: Tetralia nigrolineata Serène and Pham, 1957, ♂ (NSMT-Cr 30988; cb 5.1×cl 4.1 mm) (A) and ovig.♀ (NSMT-Cr 30988; 5.8×4.9 mm) (B). C–E: Notonyx aff. sagittifer Ng and Clark, 2010, ♂(NSMT-Cr 30991; cb 5.0×cl 3.3 mm), carapace in dorsal view (C), both chela in outer view (D) and both chelipeds in dorsal view (E).