Alainthesius signatus, Ng, Peter K. L. & Castro, Peter, 2016

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 108-114

Alainthesius signatus n. sp.

( Figs. 19 G–L; 20C, D; 27D; 34E; 48F; 55E; 83A–C)

Megaesthesius sagedae —Crosnier 1975: 110, fig. 1 [Madagascar]; Davie 2013: 475, figs. 3J–N, 4. Not Megaesthesius sagedae Rathbun, 1909 .

Type material. Holotype male (2.5 × 3.3 mm) (MNHN-IU-2013-9472, ex MNHN-B10214), Madagascar, Tulear , 23°23.0’S, 43°36.5’E, dredging, 72 m, C. Jouannic coll., 20.02 . 197372 m.

Paratype: female (2.7 × 3.0 mm) (MNHN-IU-2013-9471, ex MNHN-B10213), collected with holotype.

Diagnosis. Small size. Carapace ( Figs. 19 G; 20C, D; 27D; Crosnier 1975: fig. 1a, as Megaesthesius sagedae ) subquadrate, 1.1‒1.3 wider than long, dorsal surface smooth; front bilobed, with well-defined median cleft; anterolateral margins straight, with small, sharp teeth arranged in 3 or 4 lobes. Orbits long. Epistome ( Fig. 19 K; Crosnier 1975: fig. 1b, as M. sagedae ) compressed, posterior margin with broad median lobe with median fissure, straight lateral margins without fissures. Eye peduncle ( Figs. 19 I; 27D; Crosnier 1975: fig. 1k, as M. sagedae ) conspicuously long, immobile, cornea long, pigmentation reduced. Antennule ( Figs. 19 G, H; 27D; Crosnier 1975: 1a) greatly enlarged (particularly in males), cannot be folded. Third maxillipeds ( Fig. 34 E; Crosnier 1975: 1e) nearly fill buccal cavern when closed; merus subtriangular, outer margin convex; ischium subquadrate, about same length or longer than merus; outer margins of merus, ischium with teeth. Chelipeds ( Fig. 48 F; Crosnier 1975: fig. 1d) nearly identical in both sexes; cutting margins of both chelae with broad, shallow teeth in both sexes; small chela laterally flattened, shear-like; ventral surface of cheliped merus sometimes with obtuse tubercles. Inner margin of cheliped carpus ( Fig. 20 D) with one or more small, sharp tubercles or teeth. Ventral surface of chelipeds merus with low tubercles. Proportionally long ambulatory legs ( Fig. 19 J; Crosnier 1975: fig. 1i), 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. 19 K; 55E) broadly triangular, proportionally wide, short; fused sternites 3, 4 relatively broad. Male pleon ( Fig. 19 L; Crosnier 1975: 1b) with lateral margins of somite 6, fused somites 3–5 slightly convex; postero-lateral regions slightly swollen; telson proportionally short. 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 ( Fig. 83 A, B; Crosnier 1975: fig. 1f, g, as M. sagedae ) stout, distal segment straight with spinules. G2 ( Fig. 83 C; Crosnier 1975: fig. 1h, as M. sagedae ) about 1/2 G1, stout, distal segment long, wide, almost as long as basal segment, directed inward. Adult female unknown.

Etymology. The species name is derived from signum, Latin for “signal”, alluding to the large antennules of the species.

Remarks. The differences with A. bertrandi n. sp. are discussed under that species. Distribution. Known only from Madagascar, 72 m.

Figures

FIGURE 19. Species of Megaesthesius and Alainthesius n. gen. A, B, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.883); C ‒ F, Megaesthesius yokoyai (after Takeda & Miyake 1969 a: figs. 3 a, 4 f, 4 a, 4 e, respectively); G ‒ L, Alainthesius signatus n. sp., Madagascar: holotype male 2.5 × 3.3 mm (MNHN-IU- 2013 - 9472) (after Crosnier 1975: fig. 1 a, 1 k, 1 j, 1 b, 1 c, 1 i, respectively); M ‒ R, Megaesthesius westralia, Australia: holotype male 3.4 × 3.8 mm (after Davie 2013: figs. 1 A, B, 2 A, D, E, 3 E); S, W, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.885); T, X, Megaesthesius migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); U, Y, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073); V, Alainthesius bertrandi n. sp., Papua New Guinea: female 5.6 × 6.9 mm (MNHN-IU- 2013 - 9012). A, overall habitus; B, C, G, M, dorsal view of carapace; E, left P 4; F, I, frontal view of cephalothorax; H, O, frontal and anterolateral margin of carapace; N, ventral view of cephalothorax; J, right P 3; K, buccal cavity and posterior margin of epistome; Q, right P 4; R, right P 5; D, L, P, male pleon; S ‒ V, posterior margin of epistome; W ‒ Y, left thoracic sternites 7 and 8, “ supplementary plate ”, penis tube and penis. Abbreviations: cx 4 = coxa of P 4; cx 5 = coxa of P 5; p = penis; pt = calcified penis tube; sp = “ supplementary plate ”; st 7 = thoracic sternite 7; st 8 = thoracic sternite 8.

FIGURE 20. Overall dorsal view of species of Megaesthesius and Alainthesius n. gen. A, Megaesthesius migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); B, Megaesthesius migmus n. sp., Philippines: paratype female 3.9 × 4.5 mm (ZRC 2015.245); C, Alainthesius signatus n. sp., Madagascar: holotype male 2.5 × 3.3 mm (MNHN-IU- 2013 - 9472); D, Alainthesius signatus n. sp., Madagascar: paratype female 2.7 × 3.0 mm (MNHN-IU- 2013 - 9471); E, F, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073); G, Alainthesius bertrandi n. sp., Papua New Guinea: female 5.6 × 6.9 mm (MNHN-IU- 2013 - 9012); H, Alainthesius bertrandi n. sp., New Caledonia: female 3.4 × 4.0 mm (MNHN-IU- 2013 - 9007).

FIGURE 34. Third maxilliped of species of Megaesthesius and Alainthesius n. gen. A, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.885); B, Megaesthesius yokoyai, Japan: male 3.5 × 3.8 mm (after Takeda & Miyake 1969: fig. 4 c); C, Megaethesius westralia, Australia: holotype male 3.4 × 3.8 mm (after Davie 2013: fig. 2 C); D, Megaesthesius migmus n. sp., Philippines: paratype female 4.6 × 5.2 mm (ZRC 2015.243); E, Alainthesius signatus n. sp., Madagascar: holotype male 2.5 × 3.3 mm (after Crosnier 1975: fig. 1 e); F, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073). Scales = 0.5 mm.

FIGURE 48. Chelae of species of Megaesthesius, Alainthesius n. gen. and Microtopsis. A, B, Microtopsis takedai, Japan: holotype male 2.4 × 3.1 mm (after Komai et al. 2012: fig. 3 B, D); C, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.883); D, Megaesthesius migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); E, Megaesthesius yokoyai, Japan: male (after Takeda & Miyake 1969: fig. 4 d); F, Alainthesius signatus n. sp., Madagascar: holotype male 3.5 × 3.8 mm (after Crosnier 1975: fig. 1 d); G, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN- IU- 2013 - 9073); H, Alainthesius bertrandi n. sp., Papua New Guinea: female 5.6 × 6.9 mm (MNHN-IU- 2013 - 9012).

FIGURE 83. Gonopods of species of Alainthesius n. gen. A ‒ C, A. signatus n. sp., Madagascar: holotype male 2.5 × 3.3 mm (MNHN-IU- 2013 - 9472) (after Crosnier 1975: fig. 1 f ‒ h); D ‒ H, A. bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073). A, ventral view of right G 1; D, ventral view of left G 1; B, dorsal view of right G 1; E, G, dorsal view of distal part of left G 1; F, ventral view of distal part of left G 1; C, right G 2; H, left G 2. Scales = 0.1 mm.