Angustopelta robusta Ng & Castro, 2016, n. sp.
Creators: name: Ng, Peter K. L.
name: Castro, Peter
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Chasmocarcinidae
Angustopelta
Angustopelta robusta

description: Angustopelta robusta n. sp.
(Figs. 12 A, B; 13A‒F; 24F; 31G; 41G, H; 42A‒C; 52G; 59F, J; 74A‒E; 87C; 91C; 101F)
Type material. Holotype male (9.3 × 10.7 mm) (MNHN-IU-2010-5616), Vanuatu, Big Bay, BOA 1 stn CP2435, 14°51’10”S 166°53’80”E, 773‒900 m, 0 9.09.2005.
Paratypes: Vanuatu, MUSORSTOM 8: 1 male (10.0 × 12.6 mm) (MNHN-IU-2013-9042), stn CP1075, 15°53’S, 167°27’E, 944‒948 m, 04.10.1994; 6 males, 5 females (MNHN-IU-2013-9041), 2 males, 2 females (ZRC 2015.254, ex MNHN-IU-2013-9041), stn CP1080, 15°57’S, 167°28’E, 799‒850 m, 05.10.1994; 1 male (10.9 × 12.5 mm) (MNHN-IU-2013-9043), no other data.—SANTO 2006: 1 male (12.3 × 13.3 mm) (ZRC 2015.255) [photographed], NE Tutuba I., stn AT60, 15°33.1’S, 167°22.0’E, 880‒953 m, 03.10.2006; 1 male (8.7 × 9.1 mm) (ZRC 2015.256), W. Malo I., stn AT61, 15°39.2’S, 167°01.4’E, 266‒281 m, 0 4.10.2006.
Diagnosis. Carapace (Figs. 12 A, B; 101F) subtrapezoidal, convex, 1.1 wider than long; front bilobed, with shallow median cleft; minutely granular, without distinct lobes; anterolateral margins arcuate, round tubercle on each margin (may be absent). Eye peduncle (Fig. 24 F) filling orbit, short, immobile; cornea pigmented. Epistome (Fig. 24 F) semicircular median lobe with deep median fissure, semicircular lateral margins. Third maxilliped (Fig. 31 G) merus subcircular, ischium rectangular, slightly longer than merus. Proportionally short ambulatory legs but length varies slightly; P5 merus 0.7 cl in holotype (Fig. 42 A‒C). Chelipeds (Figs. 12 A, B; 41G, H; 101F) subequal in length, slightly dissimilar in female, heteromorphic in males; fingers of minor chela (Fig. 41 H) subcircular in cross-section, gently tapering to tip, scissor-like, cutting margins with few sharp teeth. Ventral surface of cheliped merus with 4 teeth, additional smaller teeth or large tubercles on outer margin, large tooth on distal inner margin, additional tooth on median portion may be present in some individuals. Inner margin of cheliped carpus with sharp tooth (Fig. 12 A, B). Fused thoracic sternites 1, 2 (Fig. 52 G) transversely narrow, long. Press-button for pleonal holding present as 2 small, short tubercles posterior to thoracic sternal suture 4/5, one near edge of sterno-pleonal cavity, one just outside (Fig. 59 J). Male pleon (Figs. 52 G; 59F) with proportionally short telson. G1 (Fig. 74 A‒D) stout, distal segment slightly curved, with short to long spinules, tuft of setae just before tip. G2 (Fig. 74 E) about half G1 length, curved, slender, distal segment proportionally long, curved. Female telson (Fig. 87 C) proportionally short. Vulvae (Fig. 91 C) relatively close together, located on outer margins of cavity close to suture 5/6.
Colour. The carapace is a pale, light brownish-pink and white to brownish white pereiopods after cleaning of live specimens (Fig. 101 F).
Etymology. The name is derived from the Latin robusta for “stout,” alluding to the relatively large size and stocky appearance of the species.
Remarks. The new species has a round, tooth-like tubercle on the anterolateral margin of the carapace, whereas a distinctive tooth is usually present in A. aurita and no tubercle or tooth is present in A. cribrorum. The presence of a distinct tubercle in the new species, however, is a variable one, absent or very low in three of the 20 males examined and in five of 16 females examined. It is not related to overall size, and may simply be due to variation or erosion of the tubercle due to wear and tear. In one specimen (female 9.6 × 11.0 mm, MNHN-IU-2013- 9041), there is also small sharp granule on the subhepatic region that is visible from dorsal view (Figs. 12 A, B; 13A, B, E, F). This is absent in other specimens although the surface of this region is uneven and covered with low granules. The anterolateral margin of A. modesta n. sp. has a low granule (sometimes undiscernible) that never develops into a tubercle.
Angustopelta robusta n. sp. possesses a unique double press-button of the male pleonal holding, consisting of two tubercles on each side of the pleon posterior to the thoracic sternal suture 4/5, one visible outside edge of sterno-pleonal cavity, the second adjacent to it inside the cavity (Fig. 59 J). This is unusual and present in all male specimens of this species examined, even for small specimens. The function of the second exposed tubercle is unknown. The press-button of its three conspecifics consists of only one tubercle, which may be large as in A. cribrorum (Fig. 59 I).
The ambulatory legs of the new species (Figs. 12 A, B; 42A‒C) are clearly shorter than in A. aurita (Fig. 11 B, C) and A. cribrorum (Fig. 11 D, E), the P5 merus of the folded leg almost reaching the orbits in these two species but only to the tubercle on the anterolateral margin, if present, in the new species. The shorter legs, together with a slightly broader anterior third of the carapace, give the new species a more stout appearance than its congeners.
Distribution. Only known from Vanuatu, southwestern Pacific Ocean. Depth: 266‒ 953 m.
description: Published as part of Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), pp. 1-182 in Zootaxa 4209 (1) on pages 61-63, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646