Lucascinus, Poore, Gary C. B., Guinot, Danièle, Komai, Tomoyuki & Naruse, Tohru, 2016

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 : 502

Lucascinus n. gen.

Type species. Halicarcinus bedfordi Montgomery, 1931 , herein designated.

Diagnosis. Rostrum a triangular plate ( L. bedfordi ) or rod-like spine ( L. coralicola , L. keijibabai ), 0.25–0.46 times carapace length, similar in males, females; apex with long setae. Supraocular eave arching, defined anteriorly by pseudorostral spine or tubercle, or by subrostral ridge not visible in dorsal view, posterior to pseudorostral angle; postocular angle or margin defined by sinuous anterior margin of subhepatic region. Subhepatic region with 2 tubercles on ventral margin. Carapace with well or moderately developed gastro-cardiac, thoracic grooves; without longitudinal cardiac groove; hymenosomian groove completely surrounding dorsum, isolating rostrum. Thoracic sternum of male with pleonal cavity defined laterally, anteriorly by sharp rim, about 0.4 as long as sternal length; without locking button on sternite 6. Male pleomeres 1–5, pleotelson free; pleomere 1 wider than pleomere 2, laterally lobed; pleonal margin tapering evenly from pleomere 2. Thoracic sternum of male, female with sternites 1–3 forming a separate plate, suture 3/4 being well marked, sternites 4–8 considerably enlarged, sutures 4/5–7/8 variably restricted laterally. Thoracic sternum of female with paired vulvae placed anteriorly on membranous medial area; with paired branchiosternal canal apertures ventrally on sternite 8. Pleon of ovigerous female discoid, pleomeres 1–5, pleotelson free. Antennule with broad basal article, produced laterally ( L. bedfordi , L. coralicola ) or not produced laterally ( L. keijibabai ); interantennular proepistome distinct, ridge-like, fused to epistome ( L. bedfordi , L. coralicola ) or apparently absent ( L. keijibabai ). Epistome an oblique broad plate, anterior margin ridge-like under eyes, antennae, posterior margin truncate with slight median excavation ( L. bedfordi ) or produced medially, sinuous on either side of narrow median notch ( L. bedfordi , L. coralicola ). Eyestalks moderately compact, without tubercle on anterior margin. Maxilliped 3 endopod, exposed exopod almost fully covering lateral width of buccal cavern when closed; ischium mesially expanded; axial length of ischium-merus less than twice maximum ischium width; merus with grossly expanded anterolateral lobe, exceeding buccal cavern anterolaterally or nearly so. Cheliped in male 2.5–4 times as long as carapace length; merus with swollen distal apical lobules; propodus elongate, cylindrical, fingers short, gaping at midpoint (‘nut-cracker’-like); dactylus with short proximal tooth, distal blade closing on end of fixed finger. Ambulatory legs elongate (pereopod 2 2–3 times as long as carapace length); with articulation between propodus, dactylus supported by plate on each side; dactyli mostly straight, with row of sharp spines along flexor margin. Gonopod 1 with swollen base; distal part, stout, tapering to apex directed anteriorly, distally setose. Gonopod 2 comprising a triangular base and short mesiodistal lobe about one-quarter length of base, with truncate apex. Female pleopods 2–4 biramous; pleopod 5 with exopod only; carrying c.100 embryos.

Etymology. Lucascinus honours John Lucas whose 1980 paper on Hymenosomatidae was a pioneering work and combines his name with Carcinus , a crab genus name appearing in Halicarcinus . Gender: masculine.

Included species. Lucascinus bedfordi (Montgomery, 1931) n. comb. (ex Halicarcinus ); L. coralicola (Rathbun, 1909) n. comb. (ex Rhynchoplax ); L. keijibabai (Takeda & Miyake, 1971) n. comb. (ex Rhynchoplax ).

Distribution. Southwestern Australia through the west Pacific to Japan.

Remarks. Lucascinus n. gen. comprises three species of which the males have elongate chelipeds having short ‘nut-cracker’-like fingers, straight tapering gonopod 1, distolaterally lobed merus of maxilliped 3, and free pleomeres. Lucascinus bedfordi has a shorter more triangular rostrum than the other two species of the genus whose more elongate rod-like rostrum resembles that of most species of Rhynchoplax . In as far as they are known they differ from all species of Rhynchoplax in the form of the male cheliped and gonopod 1, uniramous female pleopod 5, and in having free pleomeres in the male.