Megaesthesius westralia Davie, 2013

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 91-92

Megaesthesius westralia Davie, 2013

( Figs. 19 M–R; 34C; 82J–M)

Megaesthesius sagedae —Poore et al. 2008: 46. Not Megaesthesius sagedae Rathbun, 1909 .

Megaesthesius westralia Davie, 2013: 470 , figs. 1, 2, 3A‒E [type locality: Western Australia].

Type material. Holotype male (3.4 × 3.8 mm) ( NMV J54597 ), Australia, Western Australia, off Ningaloo, Southern Surveyor, stn SS10-2005, 22°04.00’S, 113°48.40'E, Sherman sled, 101-106 m, 10.12.2005.

Diagnosis. Carapace ( Fig. 19 M; Davie 2013: fig. 1A, B) subquadrate, 1.1 wider than long; front bilobed, with deep median cleft; dorsal surface with low, spherical tubercles. Lateral margins straight, parallel to each other, each with 4 teeth (last as large tubercle) separated by deep notches. Long orbits, eye peduncle elongated ( Fig. 19 O); Davie 2013: fig. 2A, B), immobile, cornea reduced, non-pigmented. Antennule greatly enlarged ( Fig. 19 N, O; Davie 2013: fig. 1), particularly in males. Third maxillipeds ( Fig. 34 C; Davie 2013: fig. 2C) nearly fill buccal cavern when closed; merus subtriangular, outer margin with small teeth; ischium subquadrate, outer margin with small teeth, about same size as merus; outer margins of merus, ischium with small spines. Chelipeds unknown. Proportionally short ambulatory legs ( Fig. 19 Q, R; Davie 2013: fig. 2D, E), dorsal, ventral margins of meri of P4 with minute teeth. Fused thoracic sternites 1, 2 ( Fig. 19 P; Davie 2013: fig. 1B, C) broadly triangular, proportionally broad, short. Male pleon ( Fig. 19 P; Davie 2013: fig. 3E) with lateral margins of somite 6, fused somites 3–5 nearly straight; postero-lateral regions slightly swollen; telson proportionally short. G1 ( Fig. 82 J–L; Davie 2013: fig. 3A– C) slender, distal segment straight, with spinules, apex slanted. G2 ( Fig. 82 M; Davie 2013: fig. 3D) nearly as long as G1, straight; slender, distal segment long, curved, as long as basal segment, directed inward. Female unknown.

Remarks. This species is known only from one male specimen without chelipeds. It is apparently closest to M. yokoyai , but can be separated by a suite of carapace, ambulatory legs, male pleon, and G1 characters (see key to species of Megaesthesius ).

Distribution. Known only from Western Australia. Depth: 101- 106 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 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 82. Gonopods of species of Megaesthesius. A ‒ C, M. sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.885); D ‒ F, M. migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); G ‒ I, M. yokoyai, Japan: male 3.5 × 3.8 mm (after Takeda & Miyake 1969: fig. 4 h, i); J ‒ M, M. westralia, Australia: holotype male 3.4 × 3.8 mm (after Davie 2013: fig. 3 A ‒ D). A, D, G, H, J, K, ventral view of left G 1; B, E, I, K, L, dorsal view of left G 1; C, F, M, left G 2. Scales = 0.1 mm.