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

description: Genus Alainthesius n. gen.
Megaesthesius —Crosnier 1975: 110 (part).
Type species. Alainthesius signatus n. sp. (gender masculine) Other species included:
Alainthesius bertrandi n. sp.
Diagnosis. Small size, carapace quadrate, high, front bilobed, with median cleft; anterolateral margins straight, parallel to each other, armed with small teeth arranged in 3 or 4 lobes; dorsal surface smooth. Epistome (Fig. 19 U, V) compressed, posterior margin with broad median lobe with fissure, straight lateral margins. Eye peduncle conspicuously long, immobile, cornea long, pigmentation reduced. Antennule greatly enlarged (particularly in males), cannot be folded. Third maxillipeds nearly fill buccal cavern when closed; merus subtriangular, outer margin convex; ischium subquadrate, about same length or longer than merus; outer margin with teeth (A. signatus n. sp.; Fig. 34 E) or smooth (A. bertrandi n. sp.; Fig. 34 F). Chelipeds subequal, nearly identical in both sexes; cutting margins of both chelae with broad, shallow teeth in both sexes; fingers of minor chela relatively broad, proportionally short, prominently flattened laterally, cutting margins blade-like. Inner margin of cheliped carpus with small tooth. Ventral margin of cheliped propodus with teeth. Ventral surface of chelipeds merus smooth or with low tubercles. Ambulatory legs with minute teeth or tubercles on anterior or posterior or both margins of most articles. Fused thoracic sternites 1, 2 broadly triangular, short; fused sternites 3, 4 relatively broad. Male pleon with lateral margins of somite 6, fused somites 3–5 slightly convex; postero-lateral regions slightly swollen; telson proportionally short (A. signatus n. sp.; Fig. 19 L) or long (A. bertrandi n. sp.; Fig. 55 F). Sterno-pleonal cavity of male deep, press-button for pleonal holding as tubercle at middle portion of thoracic somite 5 near edge of sternopleonal cavity. Male thoracic sternite 8 proportionally long, rectangular; “supplementary plate” conspicuously narrow, only reaching median portion of exposed thorax, short, slightly longer at rounded outer margin. Outer (ventral) surface of penis calcified, resembling plate between “supplementary plate”, sternite 8. G1 stout (A. signatus n. sp.) or slender (A. bertrandi n. sp.), distal segment straight with spinules. G2 about 1/2 G1, stout, distal segment long, wide, almost as long as basal segment, directed inward. Somites of female pleon with slightly convex lateral margins; telson proportionally long. Sterno-pleonal cavity of female deep, vulvae on outer margins of cavity between sutures 5/6, 6/7.
Etymology. The name is derived from Alain Crosnier, who described the morphology of this species (as Megaesthesius sagedae) at length, in arbitrary combination with the genus name Megaesthesius. Gender of genus masculine.
Remarks. The differences between Alainthesius n. gen. and Megaesthesius Rathbun, 1909, have been discussed under the remarks of the latter genus.
Distribution. Indo-West Pacific region: western Indian and western Pacific oceans.
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 94-106, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646