Pilumnus aff. purpureus, 1873

Sunil, Navami, Unnathpadi, Rajesh & Pullithadathil, Biji, 2023, Five Subtidal Species of the Family Pilumnidae (Crustacea, Decapoda, Brachyura) from the Philippines, with Comparative Notes on Pilumnus hirsutissimus Takeda and Komatsu, 2020, from Japan, Bulletin of the National Museum of Nature and Science. Series A, Zoology 49 (3), pp. 107-122 : 116-118

Pilumnus aff. purpureus

A. Milne-Edwards, 1873

( Figs. 5D , 7 )

Pilumnus purpureus A. Milne-Edwards, 1873, p. 246 , pl. 120 fig. 5. — Takeda & Miyake, 1968, pp. 6 (in key), 24, fig. 5a–c, pl. 2 fig. B.

Material examined. Dive site lHydee`sz, Anilao, Batangas, Luzon I., the Philippines, 15 m depth, sandy/muddy bottom; 2–X–2018; 1 ovig.8 (NMCR-92510; cb 11.4 mm including lateral spines, cl 7.9 mm); H. Takakura leg.

Remarks. The ovigerous female examined ( Fig. 7 ) is characterized by the following features: 1) The carapace is strongly convex in both directions, and comparatively wide, with 1.43 in ratio of width to length; 2) the carapace surface is smooth, without granules, ill-defined, only with shallow furrows separating the gastric and cardiac regions, and covered with short hairs interspaced with sparse longer hairs; 3) a small tuft of some feathered hairs at the anterior part of each protogastric region; 4) the frontal region is shallowly isolated from the carapace main part with a transverse furrow behind the supraorbital margin; 5) the frontal margin is declivous, cut into two truncated lobes by a median, small but distinct V-shaped notch, and fringed with small granules along whole length; 6) the lateral end of each frontal lobe is produced to be triangular lobe separated from the main lobe by a wide depression and from the supraorbital angle by a shallow and narrow depression; 7) the supraorbital margin is narrowly and slightly raised, and cut into three parts by a median small notch and an outer distinct notch; 8) the external orbital angle is tuberculate, with a corneous spinule, similar but slightly smaller than the carapace anterolateral teeth; 9) the infraorbital margin is fringed finely with spinules throughout the length, with a weakly angulated inner angle; 10) the carapace anterolateral margin behind the external orbital angle is armed with three, more or less papillate teerth tipped each with a stout corneous tubercle, which are regarded as spines; 11) the carapace anterolateral spines are subequal, or the first is slightly smaller than the posterior two teeth, being directed obliquely forwards; 12) no subhepatic tubercles or granules; 13) both chelipeds are distinctly unequal, bearing short and long hairs, and with stout tubercles except about distal lower half of the outer surface of the larger palm; 14) the ambulatory legs are comparatively stout, provided with short and long hairs, but unarmed.

The characters mentioned above agree mostly with those of Pilumnus purpureus A. Milne-Edwards, 1873 , except for some details concerning the carapace contour and anterolateral armature. In the original figure of the species by A. Milne-Edwards (1873), the carapace anterolateral margin behind the external orbital angle is illustrated as having three sharp spines, not tubercles tipped with a small horny spinule. According to Takeda and Miyake (1968), which is the sole record of P. purpureus since the original description, the carapace anterolateral spines are rather stout, curved forward and increase in size from the first to the third, and the subhepatic region is minutely granulated, one of which is prominent and visible from dorsal side but slightly smaller than the external orbital spine. Another discrepancy is the carapace proportion; it is comparatively wider in the present male from the Philippines than Takeda and Miyake`s (1968) specimens from the Ryukyu Islands (1.43 versus 1.30–1.37 in ratio of cb to cl).

Distribution. Pilumnus purpureus is known only from New Caledonia, and Okinawa-jima and Amami-Oshima Islands in the Ryukyu Islands.

Figures

Fig. 5. Posture in field, with color in life. A: Heteropilumnus planus Ng and Lin, ovig.8 (NMCR-92506; cb 10.9×cl 7.3mm). B: Pilumnus caerulescens A. Milne-Edwards, Ə (NMCR-92507; cb 11.5×cl 14.0mm). C: Pilumnus neglectus Balss, Ə (NMCR-92508; cb 8.3×cl 6.9mm). D: Pilumnus aff. purpureus A. Milne- Edwards, ovig. 8 (NMCR-92510; cb 11.4×cl 7.9 mm).

Fig. 7. Pilumnus aff. purpureus A. Milne-Edwards, ovig, 8 (NMCR-92510; cb 11.4×7.9mm). Habitus in dorsal view (A), and both chelae in outer view (B).