Megaesthesius

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 89

Key to species of Megaesthesius

1. Outer margins of ischium and merus of third maxilliped unarmed ( Fig. 34 B). Ventral margin of chela unarmed, pollex rela- tively slender; cutting margins of fingers of major male chela unarmed ( Fig. 48 E) [ Japan; East China Sea ]...... M. yokoyai

- Outer margins of ischium and merus of third maxilliped lined with small teeth or spines (e.g., Fig. 34 A). Ventral margin of chela dentiform, pollex relatively stout; cutting margins of fingers of major male chela with small teeth (e.g., Fig. 48 C)....2

2. Lateral margins of carapace with numerous prominent sharp teeth and spines ( Fig. 19 A, B) [ Singapore; Vietnam; South China Sea ; questionably from Andaman Sea]............................................................ M. sagedae

- Lateral margins of carapace with lobiform teeth, the margins can be armed with spinules (e.g., Figs. 19 M, 20A, B)........3

3. Fingers of chela prominently longer than palm ( Fig. 48 D). Ambulatory legs, especially meri, conspicuously long, relatively slender ( Fig. 20 A, B) [ Philippines].......................................................... M. migmus n. sp.

- Chela unknown. Ambulatory legs, especially meri, relatively shorter ( Fig. 19 Q, R) [Western Australia]....... M. westralia

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).