Elamena minuta A. Milne-Edwards, 1873

Poore, Gary C. B., Guinot, Danièle, Komai, Tomoyuki & Naruse, Tohru, 2016, Reappraisal of species attributed to Halicarcinus White, 1846 (Crustacea: Decapoda: Brachyura: Hymenosomatidae) with diagnosis of four new genera and one new species from New Ireland, Papua New Guinea, Zootaxa 4093 (4), pp. 480-514 : 493-494

Micas Ng & Richer de Forges, 1996

Micas Ng & Richer de Forges, 1996: 265.

Type species. Elamena minuta A. Milne-Edwards, 1873 , by original designation.

Diagnosis. Rostrum a broadly triangular projection, or a simple rod ( M. lucasi only); apex without long setae. Supraocular eave obsolete, without preocular definition or defined anteriorly by pseudorostral element of a broad triangular lobe; without postocular structures. Carapace as long as wide; with well-developed grooves, including complete or partial median cardiac groove; hymenosomian groove completely surrounding dorsum but only weakly isolating rostrum. Thoracic sternum of male with pleonal cavity defined laterally and anteriorly by sharp rim, about 0.8 of sternal length; locking button on sternite 6 unknown. Male pleomeres 1 and 2 free, 3–4 fused, 5 and pleotelson free, or pleomeres 3–pleotelson fused; pleomere 1 as wide as pleomere 2; pleonal margin tapering most strongly from pleomere 3–4. Thoracic sternum of female with paired vulvae anteriorly on membranous medial area; with paired branchiosternal canal apertures ventrally on sternite 8. Pleon of ovigerous female discoid, pleomeres 2–5 free or fused. Eyestalks compact, without tubercle on anterior margin. Maxilliped 3 endopod and exposed exopod covering almost all or three-quarters of lateral width of buccal cavern when closed; axial length of ischium-merus twice maximum ischium width; merus without expanded anterolateral lobe. Cheliped in male with grossly swollen barrel-like propodus, fingers with finely denticulate cutting edges, gape without felt of setae; dactylus usually with simple proximal tooth. Ambulatory legs elongate (pereopod 2 3 times as long as carapace length); with articulation between propodus and dactylus supported by short narrow plate on each side; dactyli curved, with 1 or 2 subterminal teeth. Gonopod 1 with swollen base, narrow distal section tapering through a sharp proximal ventral curvature and twist, with apex acute sharply bent ventrally. Female pleopods 2–5 biramous.

Included species. Micas afecundus (Lucas, 1980) (ex Halicarcinus ); M. falcipes Ng & Richer de Forges, 1996; M. filholi (De Man, 1888) (ex Elamena ) n. comb.; M. lucasi (Richer de Forges, 1993) (ex Halicarcinus ); M. minutus (A. Milne-Edwards, 1873) (ex Elamena ).

Distribution. Tropical western Pacific, subtidal to 244 m.

Remarks. Micas differs from all other taxa discussed here in having a twisted gonopod 1 with the apex bent and in having two subapical teeth on the dactylus of ambulatory legs rather than a row of several along its length. Grouping these five species on the basis of gonopod 1 (known in only three of the five species) and similar pereopodal dactyli is far from satisfactory. Micas lucasi with its rod-like rostrum is the odd one out but is too poorly known to place elsewhere with confidence. The proepistome, epistome and gonopod 2 have not been illustrated for any species in this genus.

Aletheiana Ng & Lukhaup, 2015, is known from a single cave-dwelling Indonesian species, A. tenella Ng & Lukhaup, 2015 . This too has simple dentition on the ambulatory dactyli, one subterminal tooth plus 0–3 smaller more proximal teeth. The genus differs from Micas in having narrow maxillipeds 3 only partially covering the buccual cavern (Ng & Lukhaup 2015: fig. 3E) whereas maxilliped 3 is broad and covering at least three-quarters of the buccal cavern in species of Micas (Ng & Chuang 1996: fig: 19; Ng & Richer de Forges 1996: fig. 4G). Aletheiana tenella has a more reduced rostrum and a simpler gonopod 1 without a strong curve and twist.

Another monotypic genus, Apechocinus Ng & Chuang, 1996 , shares with Micas broad maxillipeds 3, elongate and slender ambulatory legs, and a strongly twisted distal section of gonopod 1 (Ng & Chuang, 1996: fig. 4). The genus differs from Micas in having much broader rostrum that merges with the pseudorostral element (Ng & Chuang, 1996: fig. 4A) whereas the rostrum is narrower and the pseudorostral element, if any, is clearly separated from the rostrum in species of Micas ( Fig. 4 b; Lucas 1980: fig. 3G; Richer de Forges 1993: fig. 2; Ng & Richer de Forges 1996: figs. 3A, 4B).

Figures

FIGURE 4. Micas filholi (De Man, 1888). Holotype of Elamena filholi De Man, 1888, male, cl 4.0 mm, SMF ZMG 805: a, carapace and right pereopods; b, rostrum and anterior carapace; c, right pereopod 3, dactylus; d, pleon; e, gonopod 1. Scale bars a – d = 1 mm, e = 0.5 mm.