Alainthesius bertrandi, 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 : 114-129

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.

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 27. Frontal view of species of Megaesthesius and Microtopsis. A, Microtopsis takedai, Japan: paratype female 3.6 × 2.7 mm (ZRC 2012.0146); B, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.883); C, Megaesthesius migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); D, Alainthesius signatus n. sp., Madagascar: paratype female 2.7 × 3.0 mm (MNHN-IU- 2013 - 9471); E, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073); F, Alainthesius bertrandi n. sp., Papua New Guinea: female 5.6 × 6.9 mm (MNHN-IU- 2013 - 9012).

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 55. Anterior thoracic sternum and male pleon of species of Statommatia n. gen., Microtopsis and Megaesthesius. A, Statommatia granulosa n. sp., New Caledonia: holotype male 4.1 × 4.7 mm (MNHN-IU- 2013 - 9454); B, Microtopsis takedai, Japan: paratype male, carapace damaged (ZRC 2012.0146); C, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.885); D, Megaesthesius migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); E, Alainthesius signatus n. sp., Madagascar: holotype male 2.5 × 3.3 mm (MNHN-IU- 2013 - 9472); F, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073).

FIGURE 62. Thoracic sternites 7 and 8 and male pleon of species of Microtopsis and Megaesthesius. A, Microtopsis takedai, Japan: paratype male, carapace damaged (ZRC 2012.0146); B, Megaesthesius sagedae, Singapore: male 2.5 × 3.0 mm (ZRC 1995.885); C, Megaesthesius migmus n. sp., Philippines: holotype male 4.4 × 4.9 mm (NMCR); D, Alainthesius bertrandi n. sp., New Caledonia: holotype male 3.3 × 4.1 mm (MNHN-IU- 2013 - 9073).

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.

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.

FIGURE 88. Female thoracic sternum and pleon of species of Statommatia n. gen., Tenagopelta n. gen., Microtopsis and Megaesthesius. A, Statommatia apta, Philippines: female 8.5 × 10.6 mm (ZRC 2015.238); B, Statommatia malagasy n. sp., Madagascar: paratype female 9.4 × 8.1 mm (ZRC 2015.215); C, Tenagopelta pacifica n. sp., Philippines: female 9.2 × 10.4 mm (ZRC 2015.187); D, Tenagopelta brachyphallus n. sp., Australia: female 6.9 × 7.6 mm (NMV J 61680); E, Microtopsis takedai, Japan: paratype female 3.6 × 2.7 mm (ZRC 2012.0146); F, Megaesthesius sagedae, Singapore: female 3.0 × 3.6 mm (ZRC 2013.1804); G, Megaesthesius migmus, Philippines: paratype female 3.9 × 4.5 mm (ZRC 2015.245); H, Alainthesius bertrandi n. sp., Papua New Guinea: female 5.6 × 6.9 mm (MNHN-IU- 2013 - 9012). Vulvae exposed in E.

FIGURE 92. Vulvae of species of Microtopsis and Megaesthesius. A, Microtopsis takedai, Japan: paratype female 3.6 × 2.7 mm (ZRC 2012.0146); B, Megaesthesius sagedae, Singapore: female carapace length 2.9 mm, sides damaged (ZRC 1995.883); C, Megaesthesius migmus n. sp., Philippines: paratype female 3.9 × 4.5 mm (ZRC 2015.245); D, Alainthesius bertrandi n. sp., Papua New Guinea: female 5.6 × 6.9 mm (MNHN-IU- 2013 - 9012).