Alainthesius bertrandi 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
Alainthesius
Alainthesius bertrandi

description: Alainthesius bertrandi n. sp.
(Figs. 19 U, V, Y; 20E–H; 27E, F; 34F; 48G, H; 55F; 62D; 83D–H; 88H; 92D)
Type material. Holotype male (3.3 × 4.1 mm) (MNHN-IU-2013-9073), New Caledonia, MUSORSTOM 4, stn CC174, 19°0.3’S, 163°18.5’E, 365 m, 17.09.1985.
Other material examined. Papua New Guinea. PAPUA NIUIGINI 2012: 1 female (5.6 × 6.9 mm) (MNHN- IU-2013-9012), west Kranket I., stn CP3949, 05°12’S, 145°51’E, 380‒407 m, 28.11.2012.
New Caledonia. MUSORSTOM 6: 1 female, carapace partially broken (MNHN-IU-2013-9452), Loyalty Is., stn DW439, 20°46.4’S, 167°17.4’E, 288 m, 19.02.1989; 1 male (carapace partially broken, 3.4 mm carapace width) (MNHN-IU-2013-9074), Loyalty Is., stn DW442, 20°53.7’S, 167°17.10’E, 200 m, 19.02.1989.— EXBODI: 1 female (3.4 × 4.0 mm) (MNHN-IU-2013-9007), Ounia Pass, stn CP3826, 21°52’S, 166°51’E, 354‒509 m, 0 7.09.2011.
Fiji. BORDAU 1: 2 females (4.1 × 4.5 mm, 3.5 × 4.1 mm) (MNHN-IU-2013-9070), Yangasa Cluster, stn DW1496, 18°43.0’S, 178°23.0’E, 392‒407 m, 12.03.1999.
Diagnosis. Carapace (Fig. 20 E‒H) subquadrate, 1.1‒1.2 wider than long; front bilobed, with median cleft; dorsal surface smooth. Lateral margins straight, armed with small teeth arranged in 3 or 4 lobes. Long orbits, eye peduncle conspicuously long (Fig. 27 E, F), immobile, cornea reduced, non-pigmented. Epistome (Figs. 19 U, V; 27F) compressed, posterior margin with broad median lobe with fissure, straight lateral margins without fissures. Antennule (Fig. 27 E, F) greatly enlarged, particularly in males. Third maxillipeds (Fig. 34 F) nearly fill buccal cavern when closed; merus subtriangular, outer margin smooth; ischium subquadrate, outer margin smooth, longer than merus. Chelipeds (Figs. 20 G; 48G, H) subequal in length, nearly similar in both sexes; cutting margins of both chelae with broad, shallow teeth in both sexes (Fig. 48 G, H). Inner margin of cheliped carpus (Fig. 20 H) with one or more small, sharp tubercles or teeth. Proportionally long ambulatory legs (Fig. 20 E, G), P5 merus not reaching front when folded, minute teeth on anterior or posterior or both margins of most articles. Fused thoracic sternites 1, 2 (Fig. 55 F) broadly triangular, proportionally wide, short. Male pleon (Fig. 62 D) with lateral margins of fused somites 3–5, somite 6, slightly convex; telson proportionally long. Male thoracic sternite 8 (Figs. 19 Y; 62D) proportionally long, rectangular; “supplementary plate” narrow, short, slightly longer at rounded
outer margin. Outer (ventral) surface of penis calcified, resembling plate between “supplementary plate”, sternite 8 (Fig. 19 Y). G1(Fig. 83 D–G) slender, distal segment, straight, with spinules. G2 (Fig. 83 H) about 1/2 as long as G1, stout, distal segment long, wide, almost as long as basal segment, directed inwards. Somites of female pleon (Fig. 88 H) with slightly convex lateral margins; telson proportionally long. Sterno-pleonal cavity of female (Fig. 92 D) deep, vulvae far apart from each other on outer margins of cavity close to suture 5/6.
Etymology. The species is named after Bertrand Richer de Forges, whose collections in New Caledonia and the western Pacific have substantially advanced our knowledge of brachyuran diversity.
Remarks. The species is superficially similar to Megaesthesius migmus n. sp. and share a similar anterolateral armature. Alainthesius bertrandi n. sp. can nevertheless be immediately separated by its more transversely rectangular carapace (Fig. 20 E‒H) (more quadrate in M. migmus n. sp., Fig. 20 A, B), and the dorsal margin of the carpus of ambulatory legs 2‒5 is lined with spinules (Fig. 20 E) (unarmed in M. migmus n. sp., Fig. 20 A, B). The most significant difference is with the G2 structure, which in A. bertrandi n. sp. is short (Fig. 83 H) but is markedly long in M. migmus n. sp. (Fig. 82 F). For this reason, A. bertrandi n. sp. is placed in Alainthesius n. gen.
A female from Papua New Guinea, unusually large for a megaesthesiine (5.6 × 6.9 mm, MNHN-IU-2013- 9012) (Fig. 20 G) shows a pereiopod spinulation of that is somewhat different from that of the other specimens of the species that were examined, most especially a row of small teeth on the inner margin of the cheliped carpus (one tooth in other specimens). This difference is perhaps size related.
Alainthesius bertrandi n. sp. can easily be distinguished from its only known congener, A. signatus n. sp., by its more granular carapace surface (Figs. 20 E–H, 27E, F) (smoother in A. signatus n. sp., Figs. 20 C, D, 27D) and differently structured G1 (Fig. 83 D–G versus Fig. 83 A, B in A. signatus). Alainthesius bertrandi n. sp. is also found at greater depths (200–509 m) than its congener (72 m).
Distribution. Western Pacific Ocean (Papua New Guinea, New Caledonia, and Fiji). Depth: 200– 509 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 114-129, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646