Henicoplax trachydactylus, CASTRO, PETER & NG, PETER K. L., 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 : 68-73

Henicoplax trachydactylus n. sp.

( Figs. 26A–F ; 27C–F )

Type material. Male holotype, 3.4 mm × 5.3 mm ( MNHN-B29236 ) ( Figs. 26A, B ; 27C–E ); 1 female paratype, 4.4 mm × 7.2 mm ( MNHN-B29236 ) ( Fig. 26C–F ) .

Type locality. Madagascar, northeastern coast, Nosy Iranga I., 25 m, sandy bottom .

Material examined. Madagascar. Nosy Iranga I., 25 m, sand, R. Plante coll., 26.08.1965: male holotype, damaged, 3.4 mm × 5.3 mm, 1 female paratype, 4.4 mm × 7.2 mm ( MNHN-B29236 ) .

Diagnosis. Postorbital ridge of carapace absent. Chelipeds without tomentum. Cheliped dactyli granular ( Fig. 27F ). G1 with acuminate apex ( Fig. 27C, D ) (see also Table 3).

Description. Carapace ( Fig. 26A, C ) hexagonal, transversely elongated, wider than long (1.6 wider than long in male holotype), anterolateral borders nearly straight, dorsal surface without clear indication of regions; front wide, lacking median notch. Transverse depression below orbits absent. One short, triangular, obtuse (apex of right tooth acute in male holotype) anterolateral tooth posterior to triangular, anteriorly oriented outer orbital tooth. Orbits long ( Fig. 26A, C, E ), slightly longer than front (1.1 frontal width); slightly sinuous, thin supraorbital border lacking notches; suborbital border ( Fig. 26E ) sinuous, with broad median lobe, inner suborbital tooth absent. Eye peduncles long (0.6 frontal width), much longer than corneas (1.8 times cornea length in paratype); large, spherical corneas ( Fig. 26E ).

Basal antennal article slightly mobile, orbital hiatus is closed excluding antennal flagellum from orbit.

Posterior margin of epistome lobular; lateral lobes large, with straight margins, separated from median portion by deep fissure; median portion with 2 broadly rectangular lobes separated by cleft. Anterior margin of endostome well demarcated from buccal cavern, endostomial ridges low. Pterygostomian region smooth. Third maxillipeds completely closing buccal cavern; ischium rectangular with deep submedian line; merus relatively square in shape, anteroexternal part angular, rounded; exopod long, reaching to just before anterior edge of merus with long flagellum.

Cheliped fingers moderately slender, slightly longer than swollen propodus, dorsal margin of dactylus with short, rounded tubercles (very low tubercles on outer margin of propodus, carpus) ( Fig. 27F ), distal portion light in colour. Inner (dorsal) margin of carpus with small triangular tooth plus sparse, long, simple setae. Dorsal, ventral margins of ambulatory legs (P2–P5) smooth, with long, sparse simple setae; dactyli long, slen- der; P5 merus long, moderately slender, ventral margin slightly curved, distal end does not reach anterolateral tooth when folded against carapace; P5 propodus (1.1 mm long, 0.6 mm wide in holotype), proportionally stout, subcylindrical, inner margin fringed with short, simple setae, outer margin with scattered long, simple setae; P5 dactylus ( Fig. 26A–D ) proportionally slender (1.2 mm long, 0.2 mm maximum width in holotype), subcylindrical, fringed with scattered simple setae.

Thoracic sternum ( Fig. 26F ) 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 ( Fig. 26B ) deep, nearly reaching anterior margin of sternite 4, anterior extremity rounded. Press-button of male abdominal-locking mechanism not visible in holotype.

Male abdomen missing in holotype. G1 ( Fig. 27C, D ) long, slender, slightly sinuous, acuminate apex, with relatively few, small denticles; G2 ( Fig. 27E ) less than one-third of G1, straight, apex with 2 processes: one long, tip acute; second much shorter, tip obtuse. Male genital opening (gonopore) coxal; coxo-sternal disposition of long penis, protected by concave posterior portion of thoracic sternite 7.

Vulva ( Fig. 26F ) ovoid, extending across anterior portion of sternite 6 close to median axis of thorax, sternal suture 6/7 deflected; covered by soft membrane, sternal vulvar cover absent.

Colour pattern. Unknown.

Etymology. From trachys, Greek for “rough”, and dactylus, Greek for “finger”, as a noun in apposition, in reference to the granules on the dorsal surface of the cheliped dactyli that is characteristic of the new species.

Remarks. Two specimens from the northwestern coast of Madagascar, which included the damaged holotype male, are morphologically distinct from all known species of Henicoplax . n. gen. Henicoplax trachydactylus n. sp. can be distinguished from its four congeners by the presence of small tubercles on the outer surface of the cheliped dactylus, short granules on the cheliped propodus and merus ( Fig. 27F ), and the absence of postorbital ridges on the carapace ( Table 3).

Distribution. Only known from Madagascar. Depth: 25 m.

Genus Heteroplax Stimpson, 1858

Heteroplax Stimpson, 1858: 94 (40); 1907: 94 [diagnosis] (part). — De Man 1887: 89 [discussion] (part). — Alcock 1900: 292 [in list] (part). — Balss 1922a: 136 [list of species] (part); 1957: 1656 [in list] (part). — Sakai 1934: 312 [discussion] (part); 1939: 555 [in key], 560 (part); 1976: 531 (part). — Guinot 1969b: 511 [discussion] (part); 1971: 1080 [in list] (part). — Serène & Lohavanijaya 1973: 71 [discussion] (part). — Takeda & Shimazaki 1974: 60 [discussion] (part). — Karasawa & Kato 2003a: 151 [in list] (part); 2003b: 130 [in list] (part). — Ng & Castro 2007: 44 [in list] (part). — Ng et al. 2008: 78, 79 [discussion] (part).

Eucrate — Alcock 1900: 292 [in list], 298 (part). — Tesch 1918: 157 (part). — Campbell 1969: 119 [in key of species]. [not Cancer (Eucrate) De Haan, 1835 ]

not Heteroplax — Poore et al. 2008: 46. (= Neogoneplax Castro, 2007 (part), Paragoneplax Castro, 2007 (part) [ Goneplacidae ])

Diagnosis. Carapace ( Fig. 28A ) transversely elongated, much wider than long (1.5–1.6 times wider); dorsal surface smooth without clear indication of regions, continuous elevation following sinuous orbital margin from each second anterolateral tooth to just below inner limit of orbits; anterolateral borders straight, nearly parallel to each other; front wide, nearly straight with long, shallow median notch (barely visible in some individuals). Three teeth posterior to triangular, anteriorly oriented outer orbital tooth: first short, obtuse, barely visible in larger individuals; second large, triangular, with anteriorly oriented, acute tip; third short, obtuse, triangular, continuing on anterolateral border as short, shallow sulcus. Orbits long ( Fig. 28A–C ), longer than front, small notch on inner third portion of thin supraorbital border; short, triangular median lobe, inner suborbital tooth absent on thin suborbital border ( Fig. 28B, C ); eye peduncles long, almost as long as front; large, spherical corneas. Basal antennal article mobile, fills orbital hiatus excluding antennal flagellum from orbit ( Fig. 28B ). Anteroexternal margin of third maxilliped merus angular. Cheliped fingers moderately stout ( Fig. 28F ), slightly longer than swollen propodus, light in colour; carpus with tooth on inner margin; long simple, plumose setae along anterior margin of carpus. Dorsal margins of ambulatory legs (P2–P5) meri, carpi, propodi unarmed, dactyli slender, smooth, setose; P5 propodus, dactylus long, slender, subcylindrical, smooth surface, fringed with scattered, long setae. Thoracic sternum ( Fig. 28D ) wide; thoracic suture 2/3 complete, convex, close to anterior margin of sternum ( Fig. 28C ); 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. 28C, D ). Press-button of male abdominal-locking mechanism as large tubercle near thoracic suture 4/5 (small tubercle present in pre-adult females). Male abdomen narrow, slender (Tshaped), lateral margins of somites 4–6 abruptly narrowing from somite 3 to narrow telson ( Fig. 28D ); somite 3 reaching inner margins of P5 coxae; small portion on each side of thoracic sternite 8 left exposed by closed abdomen even if somite 2 transversely almost as long as somite 3 ( Fig. 28E ). G1 long, slender, sinuous, acuminate apex, with relatively large denticles ( Fig. 27G, H ); G2 less than one-third of G1, straight, apex with 2 unequal processes ( Fig. 27I ). Male genital opening (gonopore) coxal; coxo-sternal disposition of long penis, protected by concave posterior portion of thoracic sternite 7. Vulva slightly transversely elongated, across anterior portion of sternite 6 close to deflected suture 5/6; margin thick, with small, triangular lip on posterior portion; covered by soft membrane, sternal vulvar cover absent.

Type species. Heteroplax transversa Stimpson, 1858 . Subsequent designation by Guinot (1969b: 511), not H. dentatus determined by Stimpson (1858, 1907) as stated by Serène & Lohavanijaya (1973: 73); gender feminine (see Ng et al. 2008: 79, note 3).

Remarks. Serène & Lohavanijaya (1973: 71) and Ng et al. (2008: 78) discussed the status of Heteroplax . Stimpson (1858: 94 (40); 1907: 94) described the genus as “allied” to Goneplax “in the shape of the carapax [broadly transverse] and the form of the orbits [long]”. Two new species from or near Hong Kong, H. dentata and H. transversa , were included, even if the carapace of H. dentata was correctly described as “narrow”. Stimpson’s species were not figured and his material is unfortunately no longer extant. Two new species were subsequently added, H. nitida Miers, 1879 , from Korea, and H. nagasakiensis Sakai, 1934 , from Japan.

Miers (1879: 39) had doubts about the inclusion of his new species, H. nitida , in Heteroplax because of Stimpson’s (1858) description of the genus having a “basal antennal joint [that] is longer and occupies the orbital hiatus”. The second article of Miers’ specimen was described as “small, occupying the hiatus between the inner angle of the orbit and the frontal margin”. Actually, both the first and second articles fill the gap in the specimens of H. nitida examined, including the holotype. In any case, H. nitida Miers does not belong in Heteroplax and is here referred to Henicoplax n. gen. Several authors (De Man 1888, Alcock 1900, Tesch 1918, Campbell 1969) eventually considered Heteroplax as a junior synonym of Eucrate whereas most ( Balss 1922a; Sakai 1934, 1939, 1976; Guinot 1969b, 1971; Serène 1968, Serène & Lohavanijaya 1973, Serène & Soh 1976) kept them separate. Sakai (1934: 312) was nevertheless only “inclined to retain” the genus, but reiterated that the basal antennal article “differs in shape from that of “ Eucrate ” form, so that the antennal flagellum is not completely shut out from the orbit as discussed by Balss [1922a] ”. Guinot (1971: 1080) considered the genus as “very close” to Eucrate and a possible synonym (peut-être synonyme). The affinities between Stimpson’s Heteroplax dentata (placed herein in Trissoplax n. gen.) and Eucrate were in particular pointed out by several authors (see remarks for Henicoplax n. gen. below).

Serène & Lohavanijaya (1973: 71) clarified the definition of Heteroplax , gave a key to its four species known at the time, and summarized the views of various authors, particularly regarding the relationship of the genus with Eucrate . For these authors ( Serène & Lohavanijaya 1973: 71) the main differences between the two genera is that in Heteroplax : 1) the basal antennal article is mobile and does not fill and close the orbital hiatus (following Stimpson 1858, 1907; Alcock 1900; Sakai 1939) in contrast to being immobile, filling in the orbital hiatus in Eucrate , and 2) the carapace (“closer to that of Goneplax ”) and orbits are broader and the eye peduncles are longer (the “orbit breadth is as long or longer than the frontal breadth”) than in Eucrate . Confusion about the differences in the basal antennal article may have arisen from different interpretations of the character. The article is immobile in adult Eucrate because of the presence of a disto-lateral process that clearly locks the article against the margin of the orbit. The process is absent in Heteroplax and so the article may be mobile, but the article does fill the orbital hiatus.

Heteroplax is restricted here to Heteroplax transversa , its type species, on account of its wide carapace and moderately long orbits and eye peduncles ( Fig. 28A–C ). Another species, Heteroplax nitida Miers, 1879 , as well as a second species sometimes assigned to Heteroplax ( Goneplax maldivensis Rathbun, 1902 ), both having longer orbits and eye peduncles than Heteroplax sensu stricto, only one anterolateral tooth on each side of the carapace, and a postorbital ridge, are assigned to Henicoplax n. gen. Heteroplax dentata Stimpson, 1858 , is assigned to Trissoplax n. gen. because the carapace and orbits that are narrower that those in Heteroplax sensu stricto.

Two “ Heteroplax ” species from Western Australia ( Poore et al. 2008: 46) actually belong to species included in the Goneplacidae : Neogoneplax renoculis (Rathbun, 1914) and, shown in a colour photograph, Paragoneplax serenei ( Zarenkov, 1972) .

Species included.

Heteroplax transversa Stimpson, 1858

= Heteroplax nagasakiensis Sakai, 1934

The genus is restricted to the Indo-West Pacific region.

Species excluded from Heteroplax Stimpson, 1858 :

Heteroplax dentata Stimpson, 1858 (in Trissoplax n. gen.)

Heteroplax nitida Miers, 1879 (in Henicoplax n. gen.)

Goneplax maldivensis Rathbun, 1902 [“ Heteroplax ” maldivensis ( Rathbun, 1902) in Ng et al. 2008] (in Henicoplax n. gen.)

Figures

FIGURE 26. Henicoplax trachydactylus n. sp.; A, B, male holotype (3.4 mm × 5.3 mm) (MNHN-B29236), Madagascar; C–F, female paratype (4.4 mm × 7.2 mm) (MNHN-B29236), Madagascar. A, C, overall views; B, D, ventral views of carapaces; C, dorsal view of carapace; E, orbit and suborbital border; F, female thoracic sternum and vulvae. Abbreviations: s4–s7 = thoracic sternites 4 to 7, respectively; v = vulva.

FIGURE 27. A, B, Henicoplax pilimeles n. sp.; male holotype (4.2 mm × 6.8 mm) (ZRC 1984.7739–7740), Thailand, Andaman Sea coast; C–F, Henicoplax trachydactylus n. sp.; male holotype (3.4 mm × 5.3 mm) (MNHN-B29236), Madagascar; G–I, Heteroplax transversa Stimpson, 1859, male (5.8 mm × 9.5 mm) (ZRC 2008.1356), Hong Kong. A, B, P5; C, D, right G1, dorsal view; E, right G2, dorsal view; F, left cheliped, dorsal view; G, H, left G1, dorsal view; I, left G2, dorsal view. Scale bars: A, B, F, 1.0 mm; C, G, 0.5 mm; D, 0.2 mm, E, H, I, 0.1 mm.

FIGURE 28. Heteroplax transversa Stimpson, 1858; male (5.4 mm × 8.5 mm) (CBM-CZ 7310), Japan, Seto Inland Sea. A, overall view; B, frontal view showing orbits and antennae; C, third maxillipeds; D, anterior portion of male thoracic sternum and abdomen; E, posterior portion of male thoracic sternum and abdomen; F, outer views of chelae. Abbreviations: a1–a3 = male abdominal somites 1, 2, 3, respectively; cx5 = coxa of fifth pereopod (P5).