Trizocarcinus tacitus Chace, 1940

CASTRO, PETER & NG, PETER K. L., 2010, Revision of the family Euryplacidae Stimpson, 1871 (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 2375 (1), pp. 1-130 : 110-112

Trizocarcinus tacitus Chace, 1940

( Figs. 45A, B ; 46G–M )

Goneplax tridentata — Boone 1927: 10, figs. 2–4 [ Belize]; 1930: 194, pl. 66, fig. A [Florida]. [not Trapezioplax tridentata (A. Milne-Edwards, 1880) ; Pseudorhombilidae ]

Trizocarcinus tacitus Chace, 1940: 41 , figs. 15, 16 [ Barbados]; 1956: 20 [Gulf of Mexico]. — Guinot 1969b: 518, 522 [discussion], figs. 34, 43, 45, 50, 51 [holotype]; 1971: 1081 [in list]. — Soto 1985: 484, 495; 1986: 3, 4, 36; 1991: 626, 627 [Florida]. — McLaughlin et al. 2005: 257 [in list]. — Ng et al. 2008: 78 [in list].

Type material. Male holotype ( MCZ 5646 ) .

Type locality. West Indies , Barbados, 272 m.

Material examined. Bahamas. Grand Bahama, Gerda , stn. 696, 26°28’N, 78°43’W, 22.07.1965: 1 male, 14.0 mm × 18.0 mm ( RMNH D 26876) .

Florida. Florida Straits , SW of Dry Tortugas, 24.3629°N, 83.2277°W, F. F. Snelson coll., 9.05.2006: 1 male, 11.5 mm × 15.2 mm ( UF 11583 ) .

Gulf of Mexico. Oregon, stn. 273, U.S. Fish & Wildlife Service, 1951: 1 female, 23.3 mm × 31.5 mm ( USNM 92164 ) .

Guadeloupe. Mission ORSTOM, IRPM, SMCB: stn. C34, off Basse Terre, 16°22.49’N, 61°48.99’W, 405 m, G. Leblond & J. Poupin, 04.1993: 1 female, 20.6 mm × 29.4 mm ( MNHN-B30602 ) .

St. Vincent. Pillsbury , stn.876, 13°18.9’N, 61°04.7’W, 231–258 m, 06.07.1969: 1 female, 18.5 mm × 26.3 mm ( RMNH D 26875) .

Diagnosis. Dorsal, ventral surface of carapace smooth, not granular ( Fig. 45 ). Stridulating ridge absent on pterygostomian region. G1 apex not particularly long ( Fig. 46K, L ).

Remarks. Trizocarcinus tacitus , which is Western Atlantic in distribution, can be differentiated from its Tropical Eastern Pacific congener, T. dentatus , by having a characteristically smooth carapace, not granular as in the latter. Other characters separating the two species are given in the Remarks for T. dentatus .

Distribution. Western Atlantic from the Bahamas and the Gulf of Mexico to St. Vincent, West Indies. Depth: 187– 462 m.

Genus Villoplax n. gen.

Trizocarcinus — Karasawa & Kato, 2003a: 151 [in list]; 2003b: 139 [in list] [part]. — Ng & Castro 2007: 44 [in list] [part]. — Ng et al. 2008: 78 [in list] [part]. (not Trizocarcinus Rathbun, 1914 )

Diagnosis. Carapace ( Figs. 47A, B ; 48A ) quadrate, slightly wider than long, dorsal surface minutely granular, without clear indication of regions; anterolateral borders nearly straight; front wide, straight or slightly bilobed, with small median notch. One triangular anterolateral tooth with acute tips posterior to narrowly triangular, acute, anteriorly oriented outer orbital tooth. Orbits ( Figs. 47C ; 48B ) moderately transversely long (nearly as long as front); thin supraorbital margin, with 2 notches; short inner suborbital tooth, sinuous median lobe, outer notch on granular suborbital border ( Figs. 47C ; 48B ); eye peduncles moderately long, shorter than front, approximately as long as corneas; large, spherical corneas. Basal antennal article immobile, orbital hiatus is closed excluding antennal flagellum from orbit ( Fig. 47C ). Anteroexternal margin of third maxilliped merus auriculiform ( Figs. 47C ; 48B ). Cheliped fingers slender, dorsoventrally flattened, slightly shorter than propodus, light in colour; carpus with acute, curved tooth on inner margin; tomentum long, conspicuous, on outer surface of propodus, carpus, anterior margin of merus ( Figs. 47A ; 48A, C ). Dorsal margins of ambulatory legs (P2–P5) meri, carpi, propodi unarmed, dactyli slender, smooth, with conspicuous tomentum along margins; P5 propodus, dactylus long, slender, fringed with many short setae ( Figs. 47A ; 48A ). Thoracic sternum wide; thoracic suture 2/3 complete, convex, close to anterior margin ( Figs. 47D ; 48B ); 3/4 deep, short, interrupted; 4/5, 6/7, 7/8 interrupted, 5/6 complete; median groove on thoracic sternites 7, 8. Sterno-abdominal cavity of male deep, reaching anterior margin of sternite 4 ( Fig. 47D ). Press-button of male abdominallocking mechanism as large tubercle near thoracic suture 4/5 (small tubercle present in pre-adult female holotype). Male abdomen proportionally wide, triangular (not T-shaped), telson longer than wide ( Figs. 47D ; 48D ); somite 3 only slightly transversely shorter than somites 4–6, reaching inner margins of P5 coxae, fitting under episternite 7; no portions of thoracic 8 exposed by closed abdomen, somite 2 transversely almost as long as somite 3 ( Fig. 48D ). G1 long, slender, slightly sinuous, thin distal part, acuminate apex, with many denticles ( Fig. 48E, F ); G2 less than one-third of G1, apex with 2 unequal processes ( Fig. 48G ). Male genital opening (gonopore) coxal; coxo-sternal disposition of long penis, protected by slightly convex posterior portion of thoracic sternite 7. Vulva of adult female unknown but, ovoid, transversely near median portion of sternite 6 in pre-adult female.

Type species. Trizocarcinus peruvianus Garth, 1973 (by present designation, gender feminine).

Etymology. From villosus Latin for “hairy”, in reference to the thick tomentum on the chelipeds of the only species included in the new genus, Villoplax peruvianus , and plax Greek for “plate” or “tablet”, a common suffix also used for many related goneplacoid genera.

Remarks. The only species included in the new genus, V. peruvianus ( Garth, 1973) was described as a species of Trizocarcinus . Although sharing with Trizocarcinus a triangular male abdomen, the new genus departs from the two species included in Trizocarcinus by several characters related to carapace shape (straight anterolateral border each with one anterolateral tooth but arched with two teeth in Trizocarcinus ), morphology of the orbits (thin, acute outer orbital tooth and an inner suborbital tooth in contrast to a triangular outer orbital tooth and the absence of an inner suborbital tooth in Trizocarcinus ), and thoracic suture 2/3 (close to the thoracic margin but broad space between suture and margin in Trizocarcinus ) (also see Remarks for Trizocarcinus and Table 1).

Species included. Trizocarcinus peruvianus ( Garth, 1973) The genus is restricted to the Tropical Eastern Pacific region.

Figures

FIGURE 45. Trizocarcinus tacitus Chace, 1940; female (20.6 mm × 29.4 mm) (MNHN-B30602), West Indies, Guadeloupe. A, overall view; B, female thoracic sternum and vulvae. Abbreviations: mg = median groove; md = median depression; s4–s7 = thoracic sternites 4 to 7, respectively; v = vulva.

FIGURE 46. A–F, Trizocarcinus dentatus, (Rathbun, 1893) (after Guinot 1969b: figs. 37, 44, 46, 48, 49); G–M, Trizocarcinus tacitus Chace, 1940 (after Guinot 1969b: figs. 34, 43, 45, 50a, 50b, 51). A, G, frontal view showing orbits and third maxillipeds; B, H, posterior portion of male thoracic sternum, abdomen, and gonopore; C, I, anterior portion of male thoracic sternum and abdomen; D, J, posterior portion of male thoracic sternum and abdomen; E, K, L, G1; F, M, G2. Abbreviation: a2, a3 = male abdominal somites 2 and 3, respectively; g = gonopore.

FIGURE 47. Villoplax peruvianus (Garth, 1973); A, B, female holotype of Trizocarcinus peruvianus Garth, 1973 (13.1 mm × 19.1 mm) (AHF 699; now LACM); C, D, male paratype of Trizocarcinus peruvianus Garth, 1973 (19.9 mm × 28.7 mm) (AHF 705; now LACM); Perú, off Paita. A, overall view; B, dorsal view of carapace; C, frontal view showing orbits and antennae; D, ventral view of carapace. Abbreviations: a3 = male abdominal somite 3; es7 = episternite 7; s4– s7 = thoracic sternites 4 to 7, respectively; t = telson. Photo credits: J. Martin (LACM).

FIGURE 48. Villoplax peruvianus (Garth, 1973); male paratype of Trizocarcinus peruvianus Garth, 1973 (10.0 mm × 28.9 mm) (LACM), Perú, off Paita. A, overall view; B, frontal view showing third maxillipeds, orbits, and antennae; C, outer surface of right chela; D, male abdomen; E, F, G1; G, G2 (after Garth 1973: fig. 5). Abbreviations: a2, a3 = male abdominal somites 2 and 3, respectively.