Typhlocarcinops decrescens Rathbun, 1914

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 : 30

Typhlocarcinops decrescens Rathbun, 1914

( Fig. 12A–C)

Typhlocarcinops decrescens Rathbun, 1914, p. 151 .ʕ Ng and Rahayu, 2020, p. 21, figs. 16–24, 40D–F.

Not Typhlocarcinops decrescens Rathbun : Sakai, 1965, p. 171, fig. 22, pl. 84 fig. 5; 1976, p. 546, fig. 293, pl. 195 fig. 2. (= T. kanashi Ng and Rahayu, 2020 )

Typhlocarcinops genkaiae Takeda and Miyake, 1972, p. 262 , fig. 5.

Typhlocarcinops canaliculata Rathbun : Dai et al., 1986, p. 383, fig. 202 (2), pl. 55 fig. 6.ʕ Dai and Yang, 1991, p. 413, fig. 202 (2), pl. 55 fig. 6.

Material examined. Entrance to Toagel Mid in Arangel Channel, Babelthuap I., Palau Is., dredged, 40 m depth, mud; 1 8 (cb 8.6×cl 5.8 mm), NSMT-Cr 30993; June 22, 1980; K. Baba leg.

Remarks. The genus Typhlocarcinops was thoroughly revised by Ng and Rahayu (2020) who revalued the synonymity and described nine new species in addition to 13 species known at that time. The authors illustrated and described all the species based on many additional specimens and the type specimens of the known species. The real images of the species described by Rathbun (1909, 1914) were made clear, but the identification of some species is not always easy due to the variability with sexes, developmental stages and individuals. Especially, the proportion and convexity of the carapace, and the lobulation of the carapace anterolateral margin still come into question.

The female examined agrees mostly with the diagnoses of T. decrescens given by Ng and Rahayu (2020) who examined the type specimens (holotype male and paratype three males and two females from the Philippines) and two males and two females from the South China Sea , and a male from the Arafura Sea , and made clear the variations about the carapace proportion and anterolateral armature. In the present female ( Fig. 12A), the carapace is 1.48 times broader than long and seems to be proportionally wider than seven males and three females among the specimens recorded by Ng and Rahayu (2020), in which the proportion falls mostly in 1.21–1.38; the exceptional proportion exceeding this numerical value is only in a female from Shandung in China, with 1.43. The carapace of the female examined is wider than the recorded specimens, but the proportion of the carapace is variable and not always definitive character in this genus to distinguish the congeneric species as well as the front-orbital region and carapace posterior part ( Fig. 12B–C) .

Distribution. Japan, the Philippines, the South China Sea, and Indonesia, 22–29 m in depth. New to the Palau Islands.