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

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Alainthesius bertrandi

n. sp.

Alainthesius bertrandi  n. sp.

( Figs. 19View FIGURE 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.GoogleMaps 

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.GoogleMaps 

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, 19.02.1989GoogleMaps  ; 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.GoogleMaps 

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.GoogleMaps 

Diagnosis. Carapace ( Fig. 20View FIGURE 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. 27View FIGURE 27 E, F), immobile, cornea reduced, non-pigmented. Epistome ( Figs. 19View FIGURE 19 U, V; 27F) compressed, posterior margin with broad median lobe with fissure, straight lateral margins without fissures. Antennule ( Fig. 27View FIGURE 27 E, F) greatly enlarged, particularly in males. Third maxillipeds ( Fig. 34View FIGURE 34 F) nearly fill buccal cavern when closed; merus subtriangular, outer margin smooth; ischium subquadrate, outer margin smooth, longer than merus. Chelipeds ( Figs. 20View FIGURE 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. 48View FIGURE 48 G, H). Inner margin of cheliped carpus ( Fig. 20View FIGURE 20 H) with one or more small, sharp tubercles or teeth. Proportionally long ambulatory legs ( Fig. 20View FIGURE 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. 55View FIGURE 55 F) broadly triangular, proportionally wide, short. Male pleon ( Fig. 62View FIGURE 62 D) with lateral margins of fused somites 3–5, somite 6, slightly convex; telson proportionally long. Male thoracic sternite 8 ( Figs. 19View FIGURE 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. 19View FIGURE 19 Y). G1( Fig. 83View FIGURE 83 D –G) slender, distal segment, straight, with spinules. G2 ( Fig. 83View FIGURE 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. 88View FIGURE 88 H) with slightly convex lateral margins; telson proportionally long. Sterno-pleonal cavity of female ( Fig. 92View FIGURE 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. 20View FIGURE 20 E ‒H) (more quadrate in M. migmus  n. sp., Fig. 20View FIGURE 20 A, B), and the dorsal margin of the carpus of ambulatory legs 2‒5 is lined with spinules ( Fig. 20View FIGURE 20 E) (unarmed in M. migmus  n. sp., Fig. 20View FIGURE 20 A, B). The most significant difference is with the G2 structure, which in A. bertrandi  n. sp. is short ( Fig. 83View FIGURE 83 H) but is markedly long in M. migmus  n. sp. ( Fig. 82View FIGURE 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. 20View FIGURE 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. 20View FIGURE 20 E –H, 27E, F) (smoother in A. signatus  n. sp., Figs. 20View FIGURE 20 C, D, 27D) and differently structured G1 ( Fig. 83View FIGURE 83 D –G versus Fig. 83View FIGURE 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.