Pilumnus rotundus Borradaile, 1902

Manikandan, K, Megalaa, N, Valliappan, Subramanian, Nandini, K, Rani, Lourdu V, Dakshinamurthi, Senthil & Nagappan, Nagappan, 2022, Crabs (Crustacea, Decapoda) from the Seas of East and Southeast Asia Collected by the RV Hakuhō Maru (KH- 72 - 1 Cruise) 3. Sahul Shelf, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (2), pp. 35-83 : 74

Pilumnus rotundus Borradaile, 1902

( Fig. 18A–B )

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 29, 1 $ ( CB 10.6× CL 7.5 mm), NSMT-Cr 30760.

Remarks. The female examined ( Fig. 18A–B ) is characteristic in the short setae covering the carapace and the simple carapace anterolateral spines as described below, agreeing with the original figure that is somewhat diagrammatic, but enough to identify the species as P. rotundus .

This species is briefly diagnosed as follows. The carapace is covered uniformly with short, subequal setae, but not obscuring dorsal surface, without long setae and granules; the surface areolation is indistinct; the external orbital angle is armed with two spinules of equal length arranged along the carapace anterolateral margin; the anterolateral margin is armed with three, equidistant spines of equal length; each spine is perpendicular to the carapace surface, without bulged base. The outer surfaces of the cheliped carpus and palm are covered with setae similar to those on the carapace dorsal surface and armed with prominent spines similar to the three carapace anterolateral spines; the movable finger of the cheliped is also armed with slightly shorter, but similar spines on its basal half. The ambulatory legs are stout and fringed with long soft setae, with a spinule at the median part of each merus anterior margin and at the distal part of each merus and carpus anterior margin, respectively.

The type specimen of P. rotundus from Kolumdulu Atoll, Maldives, is 12 mm in breadth and 8 mm length, without record of sex. However, Deb (1987) mentioned that the original description was based on a very young specimen and quite inadequate. The female specimens newly recorded from Pearl Banks, Sri Lanka, and Port Blair, Andaman Islands, are CW 22.5mm and CL 15 mm, and CW 12 mm and CL 7 mm, respectively. Unfortunately, it is difficult to be sure of its identification and for the subsequent identification due to the inadequate description and low quality of the photograph provided by Deb (1987: pl. 12 fig. 3).

Distribution. Maldives, Sri Lanka, Andaman Islands, and now from northern Australia, 49–63 m depth.

Figures

Fig. 18.ɹA–B: Pilumnus rotundus Borradaile, $ (NSMT-Cr 30760; CB 10.6×CL 7.5 mm) from sta. 29. C: Pilumnus semilanatus Miers, $ (NSMT-Cr 30761; CB 14.7×CL 11.1mm) from sta. 29. D: Pilumnus minutus (De Haan), Ə (NSMT-Cr 30755; CB 8.9×CL 6.1mm) from sta. 29. E–F: Pilumnus longicornis Hilgendorf, Ə (NSMT-Cr 30754; CB 11.2×CL 8.6mm) from sta. 29.