Angustopelta modesta 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 modesta

description: Angustopelta modesta n. sp.
(Figs. 12 C‒H; 13G‒I; 24G, H; 31H, I; 41I, J; 42D, E; 52H; 59G, H; 74F‒I)
Type material. Holotype male (13.3 × 15.1 mm) (MNHN-IU-2013-9038), Solomon Islands, SALOMON 1, stn CP1750, 09°16’S 159°55’E, 693–696 m, 25.09.2001.
Paratypes: 3 females (largest 11.4 × 13.0 mm) (MNHN-IU-2013-9038), 2 males (11.0 × 12.6 mm, 8.7 × 9.8 mm), 1 paratype female (6.1 × 6.4 mm) (ZRC 2015.257, ex MNHN-IU-2014-12802), Solomon Islands, SALOMON 1, stn CP1750, 09°16’S, 159°55’E, 693–696 m, 25.09.2001.— 3 males (largest 11.5 × 13.2 mm), 3 females (MNHN-IU-2013-9039), 1 female (13.1 × 15.3 mm) (ZRC 2015.258), Solomon Islands, SALOMONBOA 3, Savo, stn CP2777, 09°12’S, 160°55’E, 706–722 m, 12.09.2007.
Other material examined.? Papua New Guinea. BIOPAPUA: 1 female (9.0 × 10.2 mm), Open Bay, stn CP3666, 04°40’S, 151°33’E, 760–866 m, 23.09.2010 (ZRC 2015.259, ex MNHN-IU-2011-3265); 1 female (9.3 × 9.9 mm), Southeast Point, Manus I., stn CP3689, 02°16’S, 147°29’E, 679–685 m, 29.09.2010 (MNHN-IU-2011- 3307).
Diagnosis. Carapace (Fig. 12 C‒H) subtrapezoidal, globose, quadrate appearance, 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 G, H) filling orbit, short, immobile; cornea pigmented. Epistome (Fig. 24 G, H) broad, posterior margin with semicircular median lobe with deep median fissure, semicircular lateral margins. Third maxilliped (Fig. 31 H, I) 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 D, E). Chelipeds (Figs. 12 C‒H; 41I, J) subequal in length, slightly dissimilar in female, heteromorphic in males; fingers of minor chela (Fig. 41 J) subcircular in cross-section, gently tapering to tip, scissor-like, cutting margins with few teeth. Ventral surface of cheliped merus with 4 teeth, additional smaller teeth or large tubercles on outer margin; large tooth on distal inner margin of meri. Inner margin of cheliped carpus with sharp distal tooth (Fig. 12 C‒G). Fused thoracic sternites 1, 2 (Fig. 52 H) transversely narrow, long. Press-button for pleonal holding as small, short tubercle posterior to thoracic sternal suture 4/5 near edge of sterno-pleonal cavity. Male pleon (Figs. 52 H; 59G, H) with proportionally short telson. G1 (Fig. 74 F‒H) stout, distal segment slightly curved outwards, with short to long spinules, tuft of setae just before tip, covered by pleon. G2 (Fig. 74 I) about half G1 length, curved, slender, base is proportionately slender, elongated, distal segment proportionally long, curved. Female telson proportionally short. Vulvae relatively close together, located on outer margins of cavity close to suture 5/6.
Etymology. The name is from the Latin modestus, alluding to the fact that the relatively more slender G1s are usually completely covered by the male pleon.
Remarks. The recognition of this species is warranted primarily because of the G1 structure. Although the carapace and pereiopods of A. modesta n. sp. are very similar to A. robusta n. sp., and both occur relatively close together (the former in Solomon Islands and the latter in Vanuatu), their G1s differ markedly. In A. robusta n. sp., the base of the G1 is always stout and subtruncate (Fig. 74 A, B). In A. modesta n. sp., the base of the G1 is proportionately more slender and elongated, with the distal part much longer (Fig. 74 F). This is independent of the size of the male specimens of both species examined, which supports their placement as a different species. In addition, the carapace of A. modesta n. sp. is always more quadrate in appearance, with the anterolateral margin more strongly convex and the posterolateral margins less diverging (Fig. 13 G‒I). In adult A. robusta n. sp., the anterolateral margin is less convex and the posterolateral margins diverge more, giving the carapace a more trapezoidal appearance (Fig. 13 A‒F). The carapaces of smaller specimens of A. robusta n. sp., however, can sometimes also appear more quadrate (Fig. 13 E). The ambulatory legs of A. modesta n. sp. (notably the merus) are also usually proportionately longer (Figs. 12 C‒H; 42D, E) compared to A. robusta n. sp. (Figs. 12 A, B; 42A, B), but this is not an absolute character as one specimen of A. robusta n. sp. (male 12.5 × 14.8 mm, MNHN-IU-2013- 9041) has elongated legs as well (Fig. 42 C), even though its G1 structure is typical of the species. The male pleon also appears to differ on the material examined. In addition, all male specimens of A. modesta n. sp. have fused pleonites 3–5 that are proportionately more elongated, with the sutures between the somites shallow but clearly visible (Fig. 59 G, H). In A. robusta n. sp., male pleonites 3–5 are proportionately shorter, with the sutures separating them barely visible or only more visible medially (Fig. 59 F).
The carapaces of two female specimens from Papua New Guinea (9.0 × 10.2 mm, ZRC 2015.259, ex MNHN- IU-2011-3265; 9.3 × 9.9 mm, MNHN-IU-2011-3307) closely resemble those of A. modesta n. sp. in its quadrate appearance and the presence of a distinctively low tubercle on the anterolateral margin (Fig. 12 H). The ambulatory legs of the two specimens, however, are relatively much longer (Figs. 12 H; 42F) than anything we have seen in A. modesta n. sp., A. robusta n. sp., or A. cribrorum, and suggest we are possibly dealing with an undescribed species. The absence of males, however, precludes their precise identification for the moment.
Distribution. Western Pacific Ocean (Solomon Islands, questionably from Papua New Guinea). Depth: 693‒ 722 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 59-61, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646