Heteroplax transversa Stimpson, 1858

CASTRO, PETER & NG, PETER K. L., 2010, Revision of the family Euryplacidae Stimpson, 1871 (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 2375 (1), pp. 1-130 : 73-77

Heteroplax transversa Stimpson, 1858

( Figs. 27G–I ; 28A–F )

Heteroplax transversa Stimpson, 1858: 94 (40); 1907: 95 [ Hong Kong]. — Balss 1922a: 137, fig. 2 [ Hong Kong]. — Guinot 1969b: 511 [in list]; 1971: 1080 [in list]. — Ng et al. 2008: 78, 79 [in list].

(?) Heteroplax transversa — Rathbun 1910: 342 [Gulf of Thailand]. — Naiyanetr 1998: 78 [in list]; 2007: 90 [in list] [Andaman Sea coast of Thailand].

Eucrate transversa — Tesch 1918: 158 [in key, footnote]. — Campbell 1969: 119 [in key], 132 [discussion].

Heteroplax nagasakiensis Sakai, 1934: 312 , fig. 21; 1935: 185, fig. 95; 1939: 560 [in key], 560, 722, fig. 65; 1940: 57 [in list]; 1956: 46 [in list]; 1976: 531 [in key], 531, fig. 283, pl. 191, fig. 2 [colour] [ Japan]. — Miyake 1961: 21 [in list] [ Japan]. — Miyake et al. 1962: 130 [in list] [ Japan]. — Guinot 1969b: 511 [footnote]; 1971: 1080 [in list]. — Yamaguchi et al. 1987: 22 [ Japan]. — Miyake 1991: 220 [in list] [ Japan]. — Muraoka 1998: 8 [type], 47[in list] [ Japan]. — Watanabe & Muraoka 1999: 43, fig. 2 [ Japan]. — Ng et al. 2008: 78, 79 [in list].

not Heteroplax transversus — Serène & Lohavanijaya 1973: 72 [in key], 73, 98, figs. 183, 184, pl. 18, fig. A [Gulf of Thailand]. [= Trissoplax dentata ( Stimpson, 1858) ]

Type material of Heteroplax transversa Stimpson 1858 , lost.

Type locality. Hong Kong Harbour .

Type material of Heteroplax nagasakiensis Sakai, 1974 , 1 holotype male, 7.9 mm × 12.0 mm (KPM- NH 106474); type locality: Nagasaki, Japan .

Material examined. Japan. Off Wakanoura Kishu [= Wakaura, Wakayama (?)], id. as Goneplax maldivensis by M. J. Rathbun: 1 female, 5.0 mm × 7.6 mm ( USNM 45857 ) .

Seto Inland Sea. West of Yashiro I., 33°53.80’N, 137°09’E, 18 m, TRV Toyoshio-maru, cruise 1997–05, stn. 1, S. Ohtsuka coll., 10.07.2000: 1 male, 5.4 mm × 8.5 mm, 4 females, 3.8 mm × 6.2 mm, 3.9 mm × 6.7 mm, 4.5 mm × 6.6 mm, 5.6 mm × 9.0 mm ( CBM-CZ 7310 ); East of Hashira-jima I., 34°00’N, 137°27’E, 36 m, TRV Toyoshio-maru, cruise 2000–10, stn. 2, T. Komai coll., 27.05.2005: 1 pre-adult female, 5.3 mm × 8.8, 3 females, 5.6 mm × 8.8 mm, 5.7 mm × 8.8 mm, 6.0 mm × 9.5 mm ( CBM-CZ 5603 ) .

Kyushu. Nagasaki, I. Kaneko coll.: male holotype of Heteroplax nagasakiensis Sakai, 1974 , 7.9 mm × 12.0 mm ( KPM-NH 106474 ) .

Hong Kong: 1 male, 5.8 mm × 9.5 mm, 2 detached chelipeds of smaller specimen, 1 ovigerous female, 7.3 mm × 12.3 mm, leg SWIMS ( ZRC 2008.1356 ) ; 2 ovigerous females, 6.5 mm × 10.4 mm, 6.4 mm × 10.4 mm, 3 pre-adult females, 4.4 mm × 6.7 mm, 3.2 mm × 4.8 mm, 2.5 mm × 4.0 mm, 1 pre-adult, 1.8 mm × 2.5 mm ( SWIMS CRU-XX-063 ) . – Unknown location: 1 male, 1 ovigerous female, 1 pre-adult female, 4 pre-adults ( SWIMS CRU-XX-064 ) . – Unknown location: 27.06.1988, P. Davie coll.: female, 5.7 mm × 9.1 mm ( QM W28381) .

Diagnosis. First anterolateral tooth short, barely visible in larger individuals; second large, triangular, with anteriorly oriented, acute tip; third short, obtuse, triangular, continuing on anterolateral border as short sulcus ( Fig. 28A ). Eye peduncles long, almost as long as front ( Fig. 28B, C ).

Remarks. Thirteen adult and pre-adult specimens collected from Hong Kong, the type locality of H. transversa , agree with Stimpson’s very short description (only three sentences devoted to morphology) of the species ( Stimpson 1858: 94 (40); 1907: 95). The only difference is that the size of one of Stimpson’s male specimens was given as 0.26 mm × 0.38 inches (6.60 mm × 9.65 mm), a 1:1.5 ratio. The average ratio of the seven Hong Kong male and female specimens examined (see material examined) is of 1:1.6. It is assumed that Stimpson had more than one specimen available as he gives the carapace size “in a male”. Much as a neotype for this species is needed to help stabilise the taxonomy of the species and genus, the poor condition of the specimens on hand argue against taking such an action for the moment. Certainly a neotype should be selected for the species when better preserved specimens are collectd in the future.

Some slight variations were observed among the Hong Kong specimens that were examined. The outer orbital teeth, which are typically triangular, may sometimes have a rounded anterior margin. The first anterolateral teeth, the largest and the most conspicuous of the two anterolateral teeth, always have an acute apex but their anterior margins may be straight or slightly convex. In a female specimen (6.5 mm × 10.4 mm, SWIMS CRU-XX-063 ) the left tooth was straight and triangular in shape but the right tooth had a convex margin and thus crescent in shape. Conspicuous granules, mostly rounded but some acuminate, extended from the first anterolateral teeth along both sides of the carapace just below the long orbits. Some of the granules were located at the junction of the teeth with the carapace so that the proximal margin of the teeth appeared granular. Similar granules were found in the large male holotype of H. nagasakiensis Sakai, 1974 , a junior synonym (see below). The carapace was otherwise smooth in most specimens, including that of the neotype. In the smallest pre-adults, and in contrast to adults, the outer orbital teeth ware longer than the first anterolateral teeth .

A character not mentioned in Stimpson’s description is the presence of two short, obtuse tubercles on the outer margin of the cheliped merus. Also not mentioned is the presence of short, round tubercles across the anterior third of the carapace from the anterolateral teeth to the protogastric and branchial regions, a character found only in the largest females. The G1 and G2 are illustrated herein for the first time ( Fig. 27G–I ).

In addition to Stimpson’s specimen, Hong Kong material of H. transversa was also studied by Balss (1922: 137, fig. 2). Balss’ male specimen was not found in the Zoologische Staatssammlung, Munich, where many of the specimens studied by Balss were deposited. The specimen was most probably destroyed during World War II (R. Melzer, personal communication).

Examination of the male holotype (7.9 mm × 12.0 mm, KPM-NH 106474) and the abundant available material of Heteroplax nagasakiensis Sakai, 1974 , from Japan clearly shows that it is a junior synonym of H. transversa . The nine Japanese specimens (CBM-CZ 5603, 7310; Fig. 28 ) examined here, Sakai’s description of H. nagasakiensis ( Sakai 1934: 312, fig. 21), Sakai’s subsequent treatments of the species ( Sakai 1935, 1939, 1976), and the photograph given by Watanabe & Muraoka (1999: 43, fig. 2), all agree with the Hong Kong material of H. transversa as well as Stimpson’s description of the later. The G1 of E. nagasakiensis (see Sakai 1974: fig. 283b) is also identical to that of H. transversa ( Fig. 27G, H ). Sakai (1934: 313) remarked that his new species resembled H. transversa “in outer view” but the carapace was considered to be broader in H. nagasakiensis . A Japanese specimen examined by Sakai (1976) measured 8 mm × 12.5 mm, a carapace length to carapace width ratio of 1:1.6; the same as the ratio in the nine specimens examined here, which is identical to the ratio in H. transversa (see discussion of the species above) and close to the ratio of 1:1.5 given by Balss (1922a: fig. 2). One morphological difference, however, was the slightly more rounded telson of a Hong Kong male (5.8 mm × 9.5 mm; ZRC 2008.1356) and that of the only Japanese male (5.4 mm × 8.5 mm; CBM-CZ 7310) that was examined.

The four Gulf of Thailand specimens identified by Rathbun (1910) as H. transversa were not available for examination. Heteroplax transversa is only known from Japan and Hong Kong thus far.

Campbell (1969: 132) compared H. transversa to his new species, Eucrate haswelli , a junior synonym of Stimpson’s H. dentata , which is now being placed in Trissoplax n. gen. (see Remarks for Trissoplax dentata below). Campbell included both species in Eucrate , even when he agreed that the eye peduncles of his E. transversa were long. His comments, however, were based on Stimpson’s descriptions and not on the examination of specimens of H. transversa .

The suggestion by Serène & Lohavanijaya (1973: 75) that H. nagaskiensis and H. nitida are conspecific is not correct, both species not even being congeneric.

Colour pattern. Stimpson described the colours in life of his Hong Kong specimens as similar to those of H. dentata (= Trissoplax dentata , see below). Very little colour remained in the preserved specimens from Japan that were examined (CBM-CZ 5603, 7310). Most of the specimens showed a few small, irregular lightorange marking on the dorsal surface of the carapace, pereopods (particularly the ventral surface of the chelipeds), and on the proximal portion of the cheliped dactylus. Sakai’s colour plate ( Sakai 1976: pl. 191, fig. 2) shows similar markings on the pereopods, except that the orange markings on the ambulatory legs are in the form of bands and most irregular markings on the dorsal surface of the carapace are not shown on the plate.

Distribution. Japan and Hong Kong. Depth: 18– 50 m.

Genus Machaerus Leach, 1818

Machaerus Leach, 1818: 413 . — Manning & Holthuis 1981: 161 [discussion]. — Karasawa & Kato 2003a: 151 [in list]; 2003b: 139 [in list]. — Ng & Castro 2007: 44 [in list]. — Ng et al. 2008: 78 [in list]. — De Grave et al. 2009: 33 [in list].

Diagnosis. Carapace ( Figs. 29A, C ; 30A ) hexagonal, slightly wider than long, dorsal surface smooth (except granules on hepatic region, shallow sulcus extending from each third anterolateral tooth), without clear indication of regions; anterolateral borders arched; front wide, straight, with small median notch. Three obtuse to acute anterolateral teeth posterior to triangular or rounded, obtuse, anteriorly oriented outer orbital tooth. Orbits moderately long ( Figs. 29A, C ; 30A–C ), almost as long as or slightly longer than front; 2 notches (absent in M. atlanticus ) on thin or thick supraorbital border; obtuse, salient suborbital tooth, sinuous suborbital border ( Figs. 29D ; 30B, C ); eye peduncles moderately long, slightly longer than large, spherical corneas ( Figs. 29A ; 30B, C ). Basal antennal article immobile closes orbital hiatus excluding antennal flagellum from orbit ( Fig. 30B, C ; Monod 1956: figs. 445, 451). Anteroexternal margin of third maxilliped merus angular. Cheliped fingers moderately slender ( Figs. 29A, B ; 30D ), shorter than propodus, light in colour; carpus with obtuse tooth on inner margin; dense tomentum ( Fig. 30D ) on posterior margin of propodus and anterior margin of carpus (very short in M. atlanticus ). Dorsal margins of ambulatory legs (P2–P5) meri, carpi, propodi unarmed, dactyli slender, smooth, setose. P5 propodus subcylindrical; dactylus long, slender, fringed with long setae. Thoracic sternum ( Figs. 29D ; 30F ) wide; thoracic suture 2/3 complete, convex ( Figs. 29B, D ; 30C ); 3/4 deep, short, interrupted; 4/5, 6/7, 7/8 interrupted, 5/6 complete ( Fig. 29D ); median groove on thoracic sternites 7, 8. Sterno-abdominal cavity of male deep ( Fig. 30F ), reaching anterior margin of sternite 4 ( Figs. 29B ; 30E ). Male abdomen proportionally wide, triangular (not T-shaped), proportionally narrow telson ( Fig. 30E ); somite 3 transversely longer than somites 4–6, reaching inner margins of P5 coxae, episternite 7 ( Figs. 30G ; 32A, C ); small portion on each side of thoracic sternite 8 left exposed by closed abdomen ( Figs. 30G ; 32A, C ), somite 2 slightly transversely shorter ( Figs. 30G ; 32C ) or nearly as long as somite 3 ( Fig. 32A ). Press-button of male abdominal-locking mechanism as tubercle near thoracic suture 4/5 (small tubercle present in pre-adult females). G1 long, slender, slightly sinuous, acuminate apex, with many small denticles ( Figs. 30F ; 32B, D, E ); G2 less than one-third of G1, straight, apex with 2 unequal processes ( Fig. 32F ). Male genital opening (gonopore) coxal ( Figs. 30F ; 32A, C ); coxo-sternal disposition of long penis, protected by concave posterior portion of thoracic sternite 7, expanded episternite 7 ( Fig. 30F ). Vulva ovoid ( Fig. 29D ), extending across anterior third of sternite 6 close to median axis of thorax; covered by soft membrane, sternal vulvar cover absent.

Type species. Pilumnoplax oxyacantha Monod, 1956 (subsequent designation by Manning & Holthuis 1981; gender masculine)

Remarks. Monod (1956: 350) remarked on the similarities between Eucrate and both Pilumnoplax atlantica Miers, 1881 , and his new species, P. oxyacantha . Guinot (1969b: 517) included both species in the Euryplacinae but left their generic status unresolved (pour le moment … sans attribution générique). Manning & Holthuis (1981) revised the genus and confirmed its position in the Euryplacinae . They nevertheless concluded that the genus “appears to show closest affinities with Neopilumnoplax Serène ” ( Goneplacoidea , Mathildellidae ) whereas at the same time noticing the “much slenderer male abdomen” and telson than the latter ( Manning & Holthuis 1981: 162).

Although the male abdomen of Machaerus is relatively less slender than in Eucrate and other Indo-West Pacific euryplacids, it is certainly not triangular as in the Atlantic and Eastern Pacific euryplacids, Nancyplax and Trizocarcinus ( Fig. 1 ). Despite the shape of the male abdomen, all other diagnostic characters (most especially the long and deep sterno-abdominal cavity of the male and the long and slender G1; Fig. 30F ) clearly show that Machaerus is a euryplacid.

We should also comment on the status of what has been called “ Machaerus elata ” in the literature. Boone (1927: 7, fig. 1) referred a 6.0 mm × 9.0 mm male specimen from Isla de Pinos (= Isla de la Juventud) in Cuba to “ Pilumnoplax elata ”. It was clear that Boone was identifying it with a species from west Florida, which A. Milne-Edwards (1880b: 18) had named Eucratoplax elata . Eucratoplax elata A. Milne-Edwards, 1880 , is now regarded as a species of Panoplax Stimpson, 1871 , and in the xanthoid family Panopeidae (see Guinot 1969a: 264; 1971: 1080; Ng et al. 2008: 189). Guinot (1969b: 512) noted that Boone’s (1927) “ Pilumnoplax elata ” was a problem, stating On peut se demander si la Pilumnoplax elata de Cuba figurée par BOONE (1925, pp. 7–9, fig. 1), qui ne correspond nullement à l’elata typique d’A. MILNE EDWARDS, 1880, n’est pas une Euryplax : en l’absence de figure de la face ventrale et de description des régions antennaire et abdominale, il est difficile d’avoir une certitude. Mais la forme de la carapace et surtout celle du front, où l’on devine très nettement la présence de larges lobes antéro-externes …, évoquent Euryplax et l’on pense plus particulièrement à E. polita qui, comme sur la figure de BOONE, a des dents antéro-latérales alignées et spiniformes, subégales. L’ « elata » de BOONE semble malgré tout un peu moins large que polita, laquelle offre une carapace très transverse, des dents marginales plus rapprochées; par ailleurs, il faut se rappeler que polita a été récoltée à Panama et que le Crabe de BOONE vient de Cuba ”. Guinot (1969b: 515) added: Pilumnoplax elata de Cuba signalée par BOONE (1927, p. 7, fig. 1), qui ne correspond pas à l’ elata originale d’A. MILNE EDWARDS, 1880, ni à ce que RATHBUN (1918, p. 23, pl. 23) a désigné sous ce nom, n’est bien connue que par sa face dorsale et ses appendices. Ce pourrait être un Euryplacinae : la disposition du front suggère l’existence de larges lobes externes et d’une encoche supra-orbitaire (bien sûr, en supposant que le dessin soit exact). Pour cette espèce, au sujet de laquelle nous ne pouvons pas statuer, il faut de toute façon établir une appellation spécifique nouvelle et, lorsque les caractères fondamentaux seront connues, désigner le genre qui doit la recevoir. Guinot (1969c: 714), again stated her earlier position and suggested that although similar to Trapezioplax tridentata (A. Milne-Edwards, 1880) , P. elata was distinct and that it belongs to a genus other than Trapezioplax . The records of “ Pilumnoplax elata ” by Rathbun (1898: 281; 1918: 23, pl. 3 figs. 1, 2) from Florida were referred to two new genera and two new species, Robertsella mystica and Thalassoplax angusta , by Guinot (1969c: 716, 717). The record of “ Eucratopsis elata ?” by A. Milne-Edwards & Bouvier (1923: 341, pl. 7, figs. 4, 5) remains uncertain.

Unfortunately, some authors have regarded Boone’s name as a separate and valid taxon. This may have been partly due to Guinot (1971: 1081), who placed Boone’s (1927) name with three other valid species for which the generic relationships she was not sure at the time (under Autres Euryplacinae (attribution générique à préciser )): “? [ Pilumnoplax ] elata de Boone, 1927 (nec A. Milne Edwards)”, “[ Pilumnoplax ] atlantica Miers, 1881 ”, “[ Pilumnoplax ] oxyacantha Monod, 1956 ”, and “? [ Goneplax ] maldivensis Rathbun, 1902 ”. Pilumnoplax atlantica and P. oxyacantha are now regarded as species of Machaerus , whereas G. maldivensis is being referred to a new genus, Henicoplax n. gen. (see above). Števčić (2005: 133) followed Guinot’s (1969b: 512, 513, 515, 517; 1969c: 714) observations that Boone’s (1927) “ Pilumnoplax elata ” was a problem but accepted it as a valid name (though incorrectly giving the year of Boone’s publication as 1925) and proposed a new genus, Henryalphonsia , for the species. Henryalphonsia Števčić, 2005 , is a nomen nudum as no description or diagnosis was provided. The supposed type species, “ Pilumnoplax elata Boone, 1927 ”, is not a valid name as Boone (1927) had already made it clear because her identification was based on A. Milne- Edwards’ (1880) Eucratoplax elata . Ng et al. (2008: 78) also incorrectly treated it as a valid name when they listed it as an uncertain species of Machaerus .

The figure provided in Boone (1927: fig. 1) is relatively detailed, and although the male abdomen was neither figured nor described, it in fact bears a close resemblance to what is currently identified as Trapezioplax tridentata (A. Milne-Edwards, 1880) , as was been noted by Guinot (1969b, c). We examined a photograph of Boone’s specimen (in the Peabody Museum of Natural History, Yale University, catalogue number YPM 42682) and we agree that it is probably T. tridentata or a taxon close to it. Trapezioplax is currently placed in the xanthoid family Pseudorhombilidae , and we tentatively refer Boone’s (1927) “ Pilumnoplax elata ” to the synonymy of Trapezioplax tridentata .

Species included.

Machaerus atlanticus ( Miers, 1881)

Machaerus oxyacanthus ( Monod, 1956)

The genus is restricted to the Eastern Atlantic region (West Africa).

Species excluded from Machaerus Leach, 1818 :

Pilumnoplax elata Boone, 1927 [= Trapezioplax tridentata (A. Milne-Edwards, 1880) , Pseudorhombilidae ]

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 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).

FIGURE 29. Machaerus atlanticus (Miers, 1881); A, B, male (6.5 mm × 8.9 mm) (MNHN-B 10238), Senegal, Joal; C, D, ovigerous female (6.0 mm × 8.2 mm) (MNHN-B10239), Senegal. Gorée I. A, C, overall views; B, anterior portion of male thoracic sternum and abdomen; D, female thoracic sternum and vulvae. Abbreviations: s4–s6 = thoracic sternites 4 to 6, respectively; v = vulva.

FIGURE 30. Machaerus oxyacanthus (Monod, 1956); male (19.0 mm × 30.3 mm) (MNHN-B10242), Sierra Leone. A, overall view; B, frontal view showing orbits and antennae; C, third maxillipeds; D, outer surface of left chela; E, male thoracic sternum and abdomen; F, male sterno-abdominal cavity, G1, and penis; G, posterior portion of male thoracic sternum and abdomen. 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; g = male gonopore; p = penis; s4–s8 = thoracic sternites 4 to 8, respectively.

FIGURE 32. A, B, Machaerus atlanticus (Miers, 1881) (after Guinot 1969b: figs. 36, 53, as “Pilumnoplax” atlantica); C–F, Machaerus oxyacanthus (Monod, 1956) (after Guinot 1969b: figs. 38, 54a, 54b, 55, as “Pilumnoplax” oxyacantha); G–K, Nancyplax vossi Lemaitre, García-Gómez, von Sternberg & Campos, 2001 (after Lemaitre et al. 2001: figs. 5b–e). A, C, posterior portion of male thoracic sternum, abdomen, and gonopore; B, D, E, H, I, G1; F, J, K, G2. Abbreviation: a1–a3 = male abdominal somites 1, 2, 3, respectively; g = male gonopore.