Pilumnus longicornis Hilgendorf, 1879

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 : 71-72

Pilumnus longicornis Hilgendorf, 1879

( Fig. 18E–F )

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 29, 1 Ə ( CB 11.2 mm including lateral teeth×CL 8.6 mm), NSMT-Cr 30754.

Remarks. The specimen of Pilumnus longicornis at hand is slightly smaller than the size usually seen, but is typical in the setation and armature of the carapace and ambulatory legs ( Fig. 18E ). This species is most characteristic in having three strong spines on the median to submedian parts of the anterior margin of each merus of the first three ambulatory legs, with a spine at the distal end. Otherwise, P. longicornis is characterized by the following: 1) the carapace is covered with sparse, short setae, with a line of long setae along the frontal margin and some tufts of similar setae on the protogastric and mesobranchial regions; 2) the carapace dorsal surface is shallowly separated into regions which are regularly covered with minute granules of equal size; 3) the frontal lobes are rather rounded and produced forwards; 4) the three anterolateral teeth of the carapace are each tipped with a sharp spine on the thick base, curving strongly obliquely forward; 5) both chelipeds are different in size, the merus outer margin being armed with a strong spine-tipped tubercle behind the subterminal depression followed by two much smaller tubercles; the carpus surface is wholly and equally covered with conical granules; the larger palm is smooth and polished except for the upper basal part covered with conical granules similar to those on the carpus upper surface.

Balss (1933) synonymized Pilumnus andersoni De Man, 1887 and P. tantulus Rathbun, 1923 with this species, without comment. Takeda and Miyake (1968) simply followed this conclusion, but Ng et al. (2008) listed P. tantulus as valid. The original figures of P. tantulus show the quite similar formation of the carapace and chelipeds with this species, but the ambulatory armature is described as "Ambulatory legs hairy, the merus roughened above by fine, unequal spinules."

Distribution. Widely distributed throughout the whole Indo-West Pacific, from East Africa through the Indian Ocean to the western and central Pacific, with bathymetric records from 5 to 100 m.

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.