Trissoplax tuberosa, Castro & P. K. L. Ng, 2010

CASTRO, PETER & NG, PETER K. L., 2010, Revision of the family Euryplacidae Stimpson, 1871 (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 2375 (1), pp. 1-130 : 104-109

Trissoplax tuberosa n. sp.

( Figs. 42A–E ; 43D–F )

“? Heteroplax dentatus ” — Serène & Lohavanijaya 1973: 72 [in key], 73, 98, figs. 178–182, pl. 17 [Gulf of Thailand]. Heteroplax nitidas [sic] — Serène & Soh 1976: 23 (part) [Andaman Sea]. [not Henicoplax nitida ( Miers, 1879) ]

Type material. Male holotype, 7.6 mm × 10.2 mm ( MNHN-B10340 ) ( Fig. 42 ). Type locality. Indonesia, Moluccas, Ceram , Piru Bay, Tanjung Ani, 03°14'50'' S, 128°04'20''E .

Material examined. Thailand. Andaman Sea , Thai-Danish Expedition: stn.1047-8, 05°43’N, 100°13’E, 15 m, 26.01.1966, id. as Heteroplax dentata by R. Serène: 1 feminised male parasitized by sacculinid, 3.8 mm × 4.4 mm, 1 juv. male ( ZMUC CRU-10066 ) .

Indonesia. Moluccas. Rumphius 1 Expedition : Ceram , Piru Bay, Tanjung Ani, stn. D1, 03°14'50'' S, 128°04'20''E, sand with mixed dead shells and dead corals, 23.01.1973: male holotype, 7.6 mm × 10.2 mm ( MNHN-B10340 ) .

Diagnosis. Suborbital border straight, without inner suborbital tooth or median lobe ( Fig. 42E ). Outer surface of chelipeds with spherical tubercles ( Fig. 42E ).

Description. Carapace ( Fig. 42A ) hexagonal, transversely elongated, wider than long (1.3 wider than long in male holotype), anterolateral borders nearly straight, dorsal surface without clear indication of regions; front wide, with shallow median notch, transverse sulcus along margin. Three anterolateral teeth posterior to triangular outer orbital tooth (first well developed, triangular, obtuse tip; second largest, triangular, acute tip; third short, obtuse tip); margin of teeth slightly granular, margin between outer orbital tooth, first anterolateral teeth curved, margin between first, second anterolateral teeth straight. Orbits moderately long ( Fig. 42A, E ), nearly as long as front (0.8 times frontal width in holotype); small notch on inner third portion of slightly sinuous, thin, granular (from notch to outer orbital tooth) supraorbital border; suborbital border granular, sinuous, without inner suborbital tooth or median lobe ( Fig. 42E ); eye peduncles moderately long (0.4 frontal width in holotype), much longer than corneas (2.6 times cornea length in holotype); large, spherical corneas.

Basal antennal article slightly mobile, with small disto-lateral process so that orbital hiatus is closed excluding antennal flagellum from orbit ( Serène & Lohavanijaya 1973: pl. 17, fig. A, as Heteroplax dentatus ).

Posterior margin of epistome lobular; lateral lobes large, with straight margins, separated from median portion by deep fissure; median portion with 3 lobes separated by very weak clefts, with median lobe broadly rectangular. Anterior margin of endostome well demarcated from buccal cavern, endostomial ridges low. Pterygostomian region with coarse granules. Third maxillipeds completely closing buccal cavern; ischium rectangular with deep submedian line; merus relatively square in shape but anteroexternal part angular, rounded, auriculiform; exopod long, reaching to just before anterior edge of merus with long flagellum ( Serène & Lohavanijaya 1973: fig. 178, pl. 17, fig. A, as Heteroplax dentatus ).

Cheliped fingers moderately stout, slightly longer than swollen propodus, distal portion light in colour. Outer (dorsal) surface of carpus, propodus, dactylus covered with large, spherical, mammillate tubercles ( Fig. 42E ; Serène & Lohavanijaya 1973: pl. 18, figs. C, D, as Heteroplax dentatus ). Inner (dorsal) margin of carpus with large tooth; clump of short setae on anterior margin of carpus, long plumose setae on ventral margin; outer (dorsal) margin of merus with large, obtuse, distal tooth with few, long, simple setae; median portion of ventral surface with 3, 4 rows of large, spherical tubercles. Dorsal, ventral margins of ambulatory legs (P2– P5) smooth, with long, sparse simple setae; dactyli long, slender; P5 merus long, moderately slender (4.1 mm long in holotype), ventral margin slightly arched, distal end reaches past third anterolateral tooth but not second anterolateral tooth when folded against carapace; P5 propodus (1.8 mm long, 0.8 mm wide in holotype), proportionally stout, subcylindrical, inner margin fringed with row of numerous short, simple setae, outer margin with scattered long, simple setae; P5 dactylus (2.2 mm long, 0.2 mm maximum width in holotype) proportionally slender, subcylindrical ( Fig. 42A, B ), fringed with short, simple setae.

Thoracic sternum ( Fig. 42C, D ) wide, thoracic suture 2/3 complete, convex; 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, nearly reaching anterior margin of sternite 4 ( Fig. 42D ). Press-button of male abdominal-locking mechanism not visible in holotype.

Male abdomen ( Fig. 42C ; Serène & Lohavanijaya 1973: fig. 180, as Heteroplax dentatus ) narrow, slender, transversely narrow (T-shaped), lateral margins of somites 4–6 abruptly narrowing from somite 3 to narrow, pointed telson; somite 3 reaching inner margins of P5 coxae; small portion on each side of thoracic sternite 8 left exposed by closed abdomen, somite 2 transversely almost as long as somite 3 ( Serène & Lohavanijaya 1973: fig. 180, as Heteroplax dentatus ). G1 ( Fig. 43D, E ; Serène & Lohavanijaya 1973: figs. 181, 182, as Heteroplax dentatus ) long, slender, sinuous, acuminate apex, with small denticles; G2 ( Fig. 43F ) less than onethird of G1, straight, with 2 processes: one long, tip obtuse; second much shorter, tip acute. Male genital opening (gonopore) coxal; coxo-sternal disposition of long penis, protected by concave posterior portion of thoracic sternite 7.

Female not examined (female abdomen illustrated by Serène & Lohavanijaya (1973: fig. 179, as Heteroplax dentatus ).

Etymology. From tuber, Latin for “swelling” or “bulb”, in reference to the conspicuous, spherical tubercles on the outer and dorsal surface of the chelipeds (P1) that is diagnostic of the species.

Remarks. Photographs and drawings of specimens from Manila Bay, Philippines that were identified as “? Heteroplax dentatus ” by Serène & Lohavanijaya (1973: figs. 178–182, pl. 17) clearly show that their two specimens, a male and a female, are referable to the new species. These authors did not realize that their Philippine specimens were actually different from either of Stimpson’s two species of Heteroplax , even after not- ing that H. dentata lacks the coarse cheliped granules found in their Philippine specimens, that the carapace of Stimpson’s H. dentata was narrower than that of the Philippine specimens, and that the conspicuous tomentum on the cheliped meri of Stimpson’s H. dentata was missing in the Philippine specimens.

One difference between Serène & Lohavanijaya’s specimens and the holotype is that in their male specimen the cheliped granules were “less numerous and more worn out” than in their female specimen, a situation that is evident from their photograph ( Serène & Lohavanijaya 1973: pl. 17, fig. B, D, as “? Heteroplax dentatus ”).

Two of a number of specimens from the Andaman Sea identified by Serène & Soh (1976: 23) as Heteroplax nitida (the remaining belong to Henicoplax pilimeles n. sp., see above) are also referred to T. tuberosa n. sp. The detached chelipeds of one of the two specimens (a male feminised by a sacculinid, 3.8 mm × 4.4 mm; ZMUC CRU-10066) are characteristic of the new species. The second, a very small juvenile male, had no chelipeds but both specimens are clearly conspecific and differ from T. dentata because the suborbital border lacks teeth, but possesses a defined median lobe in contrast to T. dentata ( Fig. 41A, B ).

Although close to T. dentata in the general shape of the carapace, T. tuberosa n. sp. is easily distinguished from its sole congener by the presence of coarse tubercles on the outer surface of its chelipeds (smooth in T. dentata ; Fig. 41E ), the absence of the conspicuous tomentum of T. dentata ( Fig. 39D–F ; 40A–E ; 41E ), and, as mentioned above, the absence of both, an inner suborbital tooth and a median lobe on each suborbital bor- der (both present in T. dentata ; Fig. 41A, B ).

Distribution. Andaman Sea coast of Thailand, Philippines ( Serène & Lohavanijaya 1973, as “? Heteroplax dentatus ”), Indonesia ( Moluccas). Depth: shallow subtidal of at least 15 m depth.

Genus Trizocarcinus Rathbun, 1914

Trizocarcinus Rathbun, 1914a: 117 ; 1918: 16 [in key], 17 [diagnosis]. — Balss 1957: 1656. — Guinot 1969b: 517, 518 [discussion]; 1971: 1081 [list of species]. — 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]. — De Grave et al. 2009: 33 [in list].

Diagnosis. Carapace ( Figs. 44A ; 45A ) nearly quadrate, slightly wider than long, dorsal surface granular ( T. dentatus ) or smooth ( T. tacitus ), without clear indication of regions; anterolateral borders slightly arched; front wide, straight or slightly bilobed, with small median notch. Two triangular anterolateral teeth with acute tips posterior to triangular, anteriorly oriented outer orbital tooth on outer orbital angle. Orbits ( Figs. 44B ; 45A ) moderately transversely long (shorter than front) or long (almost as long as front in T. tacitus ); thin supraorbital margin, granular or smooth, with 2 notches; inner suborbital tooth absent (only slightly elevated margin), sinuous median lobe, outer notch on granular or smooth suborbital border ( Figs. 44C ; 46A, G ); eye peduncles moderately long, shorter than front, approximately as long as corneas; large, spherical corneas ( Figs. 44B, C ; 46G ). Stridulating ridge on pterygostomian region in T. dentatus ( Rathbun 1918: fig. 3). Basal antennal article immobile, orbital hiatus is closed excluding antennal flagellum from orbit ( Figs. 44B, C ; 46A, G ). Anteroexternal margin of third maxilliped merus auriculiform ( Figs. 44C ). Cheliped fingers slender, dorsoventrally flattened, slightly shorter than propodus, light in colour ( Fig. 44D ); carpus with acute, curved tooth on inner margin; conspicuous tomentum on outer surface of propodus, carpus (plus anterior margin of merus in T. tacitus ; Figs. 44A, D ; 45A ). Dorsal margins of ambulatory legs (P2–P5) meri, carpi, propodi unarmed, dactyli slender, smooth, setose; P5 propodus, dactylus long, slender, fringed with many short setae ( Figs. 44A ; 45A ). Thoracic sternum ( Figs. 44F ; 45B ; 46C; 46I ) wide; thoracic suture 2/3 complete, slightly convex ( Fig. 45B ); 3/4 deep, short, interrupted; 4/5, 6/7, 7/8 interrupted, 5/6 complete ( Fig. 45B ); median groove on thoracic sternites 7, 8. Ovoid concavity on anterior portion of sternite 1–2. Sterno-abdominal cavity of male deep, reaching anterior margin of sternite 4 ( Fig. 46C, I ); sterno-abdominal cavity of female with deep, wide depression along median portion of sternite 4 ( Fig. 45B ). Press-button of male abdominal-locking mechanism as large tubercle near thoracic suture 4/5 (small tubercle present in pre-adult females). Male abdomen proportionally wide, triangular (not T-shaped), telson longer than wide ( Figs. 1A ; 44E ); somite 3 only slightly transversely shorter than somites 4–6, reaching inner margins of P5 coxae, fitting under episternite 7 ( Fig. 44G ; 46D; 46J ); small portion on each side of thoracic sternite 8 left exposed by closed abdomen, somite 2 transversely shorter than somite 3 ( Fig. 44G ). G1 long (particularly in T. dentatus , which has long, thin distal part), slender, slightly sinuous, with many small denticles, acuminate apex ( Figs. 44F ; 46E, K ); G2 less than onethird of G1, apex with 2 unequal processes ( Fig. 46F, M ). Male genital opening (gonopore) coxal ( Fig. 46B, H ); coxo-sternal disposition of long penis, protected by slightly convex posterior portion of thoracic episternite 7 ( Fig. 44F ). Vulva relatively large, ovoid, transversely near median portion of sternite 6, extending across median half of sternite ( Fig. 45B ); thick, elevated outer-posterior margin; covered by soft membrane, sternal vulvar cover absent.

Type species. Carcinoplax dentatus Rathbun, 1893 (by monotypy, gender masculine).

Remarks. The proportionally wide, triangular male abdomen of Trizocarcinus ( Figs. 1A , 44E ) contrasts with the T-shaped abdomen of most other euryplacids, a character shared with Nancyplax and Villoplax n. gen. (see Remarks for Euryplacidae ). The G1 is particularly long, with a narrow distal part, in T. dentatus ( Figs. 44F ; 46E ), longer than in its congener T. tacitus and all other euryplacids except one (see below). All other characters, however, clearly argue for its inclusion in the Euryplacidae (see Guinot 1969b: 518).

Trizocarcinus peruvianus Garth, 1973 , like T. dentatus also described from the Tropical Eastern Pacific region, is being referred to Villoplax n. gen. (see below). Trizocarcinus dentatus appears to be sympatric with V. peruvianus ( Garth, 1973) , along its southernmost distribution in northern Perú. Both species share a conspicuous tomentum and a G1 with a long, narrow apex. Other characters, most importantly the shape of the carapace, nevertheless provide evidence of their inclusion in separate genera (see Remarks for Villoplax n. gen. and Table 1).

Species included.

Trizocarcinus dentatus ( Rathbun, 1893)

Trizocarcinus tacitus Chace, 1940

The genus is restricted to the Western Atlantic and Tropical Eastern Pacific regions.

Species excluded from Trizocarcinus : Trizocarcinus peruvianus Garth, 1973 (= Villoplax peruvianus ( Garth, 1973))

Figures

FIGURE 1. Variation in the shape of the male abdomen among the genera of Euryplacidae. A, Trizocarcinus dentatus (Rathbun, 1893); male (14.7 mm × 20.2 mm) (MNHN-B20990), Mexico, Gulf of California; B, Machaerus oxyacanthus (Monod, 1956), male (19.0 mm × 30.3 mm) (MNHN-B10242), Sierra Leone; C, Systroplax angusta (Rathbun, 1914), male (32.3 mm × 37.2 mm) (MNHN-B29377), Fiji; D, Eucrate solaris Yang & Sun, 1979, male (23.3 mm × 28.1 mm) (ZRC 2008.1333), Philippines, Bohol, Panglao. Abbreviations: a3 = abdominal somite 3.

FIGURE 39. Colours in life. A, Euryplax nitida Stimpson, 1871; male neotype (7.1 mm × 11.3 mm) (UF 15166), Gulf of Mexico; B, Euryplax nitida Stimpson, 1871; male (4.4 mm × 7.0 mm) (UF 15168), Gulf of Mexico; C, Psopheticoides sanguineus Sakai, 1969, male (22.2 mm × 26.7 mm) (MNHN-B29728), Philippines, Bohol, Panglao; D, Trissoplax dentata (Stimpson, 1858), male (6.2 mm × 8.3 mm) (NHM), Thailand, Andaman Sea; E, Trissoplax dentata (Stimpson, 1858), young male, not preserved, Singapore, Changi; F, Trissoplax dentata (Stimpson, 1858), female (8.7 mm × 11.5 mm) (ZRC 2000.2240), Singapore. Photo credits: A, B by Florida Museum of Natural History (UF); D by P. F. Clark (NHM).

FIGURE 40. Trissoplax dentata (Stimpson, 1858); A, male neotype of Heteroplax dentatus Stimpson, 1858 (16.4 mm × 21.5 mm) (QM W27400), Hong Kong, Tolo Harbour; B, male holotype of Eucrate haswelli Campbell, 1969 (15.0 mm × 19.5 mm) (AM P6991), Australia, Queensland, Port Denison; C, male (20.0 mm × 26.2 mm) (ZRC 2008.1236), Singapore, Changi Point; D, male lectotype of Eucrate affinis Haswell, 1882 (6.6 mm × 8.7 mm) (AM P2972), Australia, Queensland, Port Denison; E, male paratype of Eucrate costata Yang & Sun, 1979 (25.0 mm × 19.0 mm) (BMNH J79140), China, Dongshan, Fujian Province; F, pre-adult female holotype of Pseudorhombila sulcatifrons var. australiensis Miers, 1884 (8.4 mm × 6.0 mm) (NHM 1882.93), Australia, Queensland, Port Molle. A–C, E, F, overall views; D, dorsal view of carapace. Photo credits: D by R.T. Springthorpe © (AM), F by P. Crabb (NHM).

FIGURE 41. Trissoplax dentata (Stimpson, 1858); A–D, F, male neotype of Heteroplax dentatus Stimpson, 1858 (16.4 mm × 21.5 mm) (QM W27400), Hong Kong, Tolo Harbour; E, male (20.0 mm × 26.2 mm), Singapore, Changi Point; G, female (8.7 mm × 11.5 mm) (ZRC 2000.2240) (ZRC 2008.1236), Singapore. A, frontal view showing third maxillipeds; B, frontal view showing orbits and antennae; C, anterior portion of male thoracic sternum; D, posterior portion of male thoracic sternum and abdomen; E, outer surface of right chela; F, male sterno-abdominal cavity, G1 and penis; G, female thoracic sternum and vulvae. Abbreviations: a1–a3 = male abdominal somites 1, 2, 3, respectively; cx5 = coxa of fifth pereopod (P5); es7 = episternite 7; G1 = first male pleopod; G2 = second male pleopod; mg = median groove; p = penis; s4–s7 = thoracic sternites 4 to 7, respectively; vc = sternal vulvar cover.

FIGURE 42. Trissoplax tuberosa n. sp.; male holotype (7.6 mm × 10.2 mm) (MNHN-B10340), Indonesia, Moluccas. A, overall view; B, ventral view of carapace; C, anterior portion of male thoracic sternum and abdomen; D, male sternoabdominal cavity and G1; E, frontal view showing orbits, antennae and outer surfaces of chelae. Abbreviations: G1 = first male pleopod; sc = sterno-abdominal cavity. Photo credits: A, B by H. H. Tan (ZRC).

FIGURE 43. Gonopods. A–C, Trissoplax dentata (Stimpson, 1859); male neotype of Heteroplax dentata Stimpson, 1859 (16.4 mm × 21.5 mm) (QM W27400); D–F, Trissoplax tuberosa n. sp., male holotype (7.6 mm × 10.2 mm) (MNHN-B10340), Indonesia, Moluccas. A, B, D, E, right G1, dorsal view; C, F, right G2, dorsal view. Scale bars: A, 1.0 mm; B, D, 0.5 mm; C, E, F, 0.2 mm.

FIGURE 44. Trizocarcinus dentatus (Rathbun, 1893); male (14.7 mm × 20.2 mm) (MNHN-B20990), Mexico, Gulf of California. A, overall view; B, frontal view showing orbits and antennae; C, third maxillipeds; D, outer surface of right chelae; E, anterior portion of male thoracic sternum and abdomen; F, posterior portion of male thoracic sternum and abdomen; G, male sterno-abdominal cavity, G1, and penis. Abbreviations: a1–a3 = male abdominal somites 1, 2, 3, respectively; cx5 = coxa of fifth pereopod (P5); es7 = episternite 7; G1 = first male pleopod; mg = median groove; p = penis; s6–s8 = thoracic sternites 6 to 8, respectively.

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.