Ethusina coronata, Castro, 2005

Castro, Peter, 2005, Crabs of the subfamily Ethusinae Guinot, 1977 (Crustacea, Decapoda, Brachyura, Dorippidae) of the Indo-West Pacific region, Zoosystema 27 (3), pp. 499-600 : 555-559

Ethusina coronata n. sp.

( Fig. 19 )

Ethusina robusta – Chen 2000: 430 (part), fig. 3 (not E. robusta ( Miers, 1886)) .

TYPE MATERIAL. — Holotype: cl 12. 1 mm, cw 12.0 mm, SOLOMON 1, stn CP 1764 ( MNHN- B 28734); paratype: cl 11.4 mm, cw 10.9 mm, MUSORSTOM 8, stn CP 1037 ( MNHN-B 27516 ).

The holotype is a male parasitized by Sacculina sp. but there was no evidence of morphological abnormalities. The carapace of two other males in the collection were badly damaged; a third male had already been illustrat- ed by Chen (2000: fig. 3).

TYPE LOCALITY. — Solomon Is, Indispensable Strait W of Malaita island, 08°36.6’S, 160°07.4’E, 1327- 1598 m.

MATERIAL EXAMINED. — Solomon Islands. SALOMON 1, stn CP 1764, 08°36.6’S, 160°07.4’E, 1327-1598 m, 27.IX.2001, 1 holotype, parasitized by Sacculina sp. ( MNHN-B 28734).

?SALOMON 1, stn CP 1752, 09°06.9’S, 159°53.2’E, 896-912 m, 25.IX.2001, 1 ( MNHN-B 28675).

Vanuatu. MUSORSTOM 8, stn CP 992, 18°52.34’S, 168°55.16’E, 775- 748 m, 29.IX,1994, 1 parasitized by Sacculina sp. ( MNHN-B 28662). — Stn CP 1037, 18°03.70’S, 168°54.40’E, 1058-1086 m, 24.IX.1994, 1 paratype ( MNHN-B 27516).

New Caledonia. BATHUS 1, stn CP 651, 21°41.80’S, 166°40.10’E, 1080 m, 11.III.1993, 1 ( MNHN-B 28663).

BATHUS 4, stn DW 884, 22°05.03’S, 165°56.63’E, 1100-1200 m, 1.VIII.1994, 1 ( MNHN-B 28664). ETYMOLOGY. — From corona, Latin for crown, in reference to the long, slender, typically outwardly orient- ed outer orbital teeth, which, together with the long and acute frontal teeth, give the anterior end of the carapace a crown-like appearance.

DISTRIBUTION. — Known from Vanuatu ( Chen 2000, as E. robusta ) and here from the Solomon Is and New Caledonia. Depth: 748-1598 m ( Fig. 34 ).

SIZE. — Maximum size: cl 12.1 mm, cw 12.0 mm ( MNHN-B 28734), cl 13.7 mm, cw 14.1 mm ( MNHN-B 28664).

DESCRIPTION

Carapace ( Fig. 19A ; Chen 2000: fig. 3, as Ethusina robusta ( Miers, 1886)) slightly longer than broad in males, wider in single female specimen; dorsal surface with very short setae, small granules. Urogastric, cardiac regions elevated, urogastric region bordered by conspicuous lateral grooves; branchial grooves shallow. Branchial regions inflated along sides, particularly in female specimen. Anterior border of carapace with triangular, slen- der, acutely tipped, outwardly directed (except in male paratype; Chen 2000: fig. 3, as E. robusta ) outer orbital teeth, reaching as high or nearly as high as frontal teeth. Frontal teeth longer, more conspicuous in males than female specimen, acute tips; lateral frontal teeth slender, nearly equal or slightly longer than triangular, acutely tipped (obtuse in female specimen) median frontal teeth. Orbital sinuses broad, V-shaped; inner margins slightly curved, outer nearly straight; lateral frontal sinuses U-shaped, asymmetrical in males, symmetrical in female specimen; median frontal sinus V-shaped, wider than lateral frontal sinuses but narrower than orbital sinuses.

Eye peduncles wide, slightly longer than or as long as cornea, immobile. Distalmost portion of peduncles, most of eyes visible dorsally.

Anterior border of endostome lies well below posterior border of antennular fossae of basal antennular articles.

Male chelipeds (P1) smooth, equal or nearly equal ( Chen 2000: fig. 3b, c, as E. robusta ); propodi swollen, almost as long as fingers; fingers slender, with broad cutting edges. Chelipeds of female specimen similar to male chelipeds except more slender propodi, no defined cutting edges on fingers.

P2, P3 ( Fig. 19A ; Chen 2000: fig. 3d, as E. robusta ) relatively short and thick; smooth; length of P2 meri 0.8-0.9 times cl, P2 meri 6.1-6.3 times longer than broad in males, 7.9 in female specimen. P4, P5 with short hairs; P5 dactyli relatively slender, curved ( Chen 2000: fig. 3e, as E. robusta ). Male abdomen ( Chen 2000: fig. 3f, as E. robusta ) with four somites (3-5 fused, basal half swollen), triangular telson. Somite 1 length three times as broad, somite 6 rectangular. Female abdomen with six somites, broad, triangular telson; somite 3 broadest, somite 6 longest.

G1 ( Fig. 19B ; Chen 2000: fig. 3g, as E. robusta ) stout; distal third narrower than proximal, conspicuously twisted, slightly curved, fringed by setae, each tip slightly pointed, short spines along dorsal surface; G2 ( Chen 2000: fig. 3h, as E. robusta ) relatively short, distal third straight, broad distal ends, blunt tips.

REMARKS

Ethusina coronata n. sp. shares prominent, slen- der but triangular outer orbital and frontal teeth with E. pubescens Chen, 1993 ( Chen 1993: fig. 19a). Nevertheless, the outer orbital teeth are much shorter, P2 and P3 more slender, and the carapace is covered by a more distinctive pubescence in E. pubescens .

A male specimen of the new species (cl 10.9 mm, cw 9.8 mm, MNHN-B 27516) was identified as E. robusta ( Miers, 1886) by Chen (2000: 430, fig. 3). It is clearly not conspecific with E. robusta , having wider, triangular outer orbital teeth and shorter, stouter P2-P5 dactyli than Miers’ species ( Fig. 25A ; Miers 1886: pl. 29, fig. 2). There are also differences in the G1 and G2, the G1 being flattened, not twisted, in E. robusta ( Fig. 25B ; Chen & Xu 1991: fig 9.2). In fact, none of the other material identified by Chen (2000) as E. robusta proved to belong to Miers’ species but to E. coronata n. sp. and two other species, E. vanuatuensis Chen, 2000 , and E. ciliacirrata n. sp.

A female from the Solomon Is (cl 13.7 mm, cw 14.1 mm, MNHN-B 28664), the only female in the collection, had more slender P2 and P3, the meri of P2 7.9 times longer than broad in contrast to 6.1-6.3 in the males. A similar sexual dimorphism, however, was observed in Ethusina stenommata n. sp. (see below), where more than one female specimen were available. A second, incomplete female from the same location (cl 12.2 mm, cw 12.3 mm, MNHN-B 28675) was questionably identified as belonging to E. coronata n. sp. The carapace, P2, and P3 were similar to the first female but of the partially severed outer orbital teeth only the left one is slightly directed outwardly and the right one is straight.

Ethusina desciscens ( Alcock, 1896) ( Fig. 20 )

Ethusa (Ethusina) desciscens Alcock, 1896: 286 ; 1899: 35.

Ethusa desciscens – Alcock & MacGilchrist 1905: pl. 72, fig. 2, 2a.

Ethusina desciscens – Doflein 1904: 292 (list), fig. 65. — Ihle 1916b: 153 (list), 156 (list). — Serène 1968: 40 (list). — Chen 1987: 689, fig. 7, pl. 2, fig. F; 1993: 336 (key). — Ng & Ho 2003: 72 (list).

Not Ethusina desciscens – Chen 1985: 197, figs 15, 16, pl. 1, figs 4, 5 (= E. chenae Ng & Ho, 2003 ).

Not Ethusina desciscens – Chen 1986: 136, fig. 15; 1993: 336 (key). — Chen & Sun 2002: 54, 251, fig. 108 (= E. taiwanensis Ng & Ho, 2003 ?).

Not Ethusina desciscens – Chen 1993: 336 (key), 337; 1997: 624; 2000: 427 (= E. robusta ( Miers, 1886)) .

Not Ethusina descisces [sic] – Chen 1998: 234 (= E. taiwanensis Ng & Ho, 2003 ?).

TYPE MATERIAL. — Unknown (Zoological Survey of India, Calcutta?).

TYPE LOCALITY. — India, Andaman and Laccadive seas.

MATERIAL EXAMINED. — Madagascar. Vauban, stn CH 127, 18°00’S, 43°00’E, 1715-1750 m, A. Crosnier coll., 16.I.1975, 1 ( MNHN-B 18364). — Stn CH 131, 13°46’S, 47°33’E, 1490-1600 m, A. Crosnier coll., 20.I.1975, 1 ( MNHN-B 18357). — Stn CH 138, 13°48.8’S, 47°29.4’E, 1800-2000 m, A. Crosnier coll., 27.II.1975, 2 ( MNHN-B 18354). — Stn CH 142, 13°45.6’S, 47°34.2’E, 1250- 1300 m, A. Crosnier coll., 28.II.1975, 1 ( MNHN- B 18277).

DISTRIBUTION. — Madagascar (Chen 1987), eastern India ( Alcock 1896, 1899). Depth: 485 ( Alcock 1896) - 2000 m ( Fig. 34 ).

SIZE. — Maximum size: cl 7.2 mm, cw 7.4 mm (MNHN-B 18277), cl 12.3 mm, cw 11.7 mm (MNHN-B 18354).

REMARKS

In his description, Alcock characterized Ethusina desciscens as close to E. investigatoris ( Alcock, 1896) , a junior subjective synonym of E. robusta ( Miers, 1886) , except for three differences: eye peduncles that are more mobile than in E. investigatoris sensu Alcock , a smaller size, and male chelipeds that are dissimilar in size ( Alcock 1896: 286). Another character not mentioned by Alcock but apparent in drawings of his material is the shape and length of the outer orbital teeth: longer in E. robusta , almost reaching the lateral frontal teeth ( Alcock & MacGilchrist 1905: pl. 72, fig. 3, 3a, as E. investigatoris ), than in E. desciscens , where the outer orbital teeth reach only a short distance above the base of the lateral frontal teeth. The outer orbital teeth of E. robusta , however, were described as each having a tip that “falls considerably short of the tips of the rather long acute frontal spines” ( Alcock 1896: 285, as E. investigatoris ). In fact, the length of the outer orbital teeth varies widely, a case similar to that of Ethusa indica Alcock, 1894 (see above). Large specimens that agree with the definition of E. desciscens (cl 11.0 mm, cw 11.0 mm,

cl 12.3 mm, cw 11.7 mm, MNHN-B 18354) have outer orbital teeth that are longer than the lateral frontal teeth. A similar condition, however, is found in E. investigatoris sensu Alcock (see Remarks of E. robusta below). Another, and more significant, difference shown in the drawings of Alcock’s material is the length of the eye peduncles, much longer in E. robusta ( Alcock & MacGilchrist 1905: pl. 72, fig. 3a, as E. investigatoris ) than in E. desciscens ( Alcock & MacGilchrist 1905: pl. 72, fig. 2a). Alcock (1899: 35) considered the presence in E. desciscens of eye peduncles that are relatively mobile as “the connecting-link between Ethusa and Ethusina ”. This, however, was not noticed in any of the Madagascar specimens that were examined. The apparent “mobility” of eye peduncles could simply depend on how long specimens have been fixed. There are also some very slight differences in the G1, being relatively more slen- der and narrow distally in E. desciscens ( Fig. 20A ) than in E. robusta ( Fig. 25A ). The G2 also show some differences, being relatively shorter and stouter in E. desciscens ( Fig. 20 B) than in E. robusta ( Fig. 25C ).

Alcock (1896: 286) described E. desciscens as a separate species but explained that he “should have regarded it as a variety of E. investigatoris but that two specimens coming from very different localities and depths present the same peculiarities”. One of his specimens came from the Andaman Sea at a depth of 485 m and the second from the Laccadive Sea at a depth of 1669-1703 m. The examination of the type material of both species, however, could clarify the problem. The material, if extant, is supposedly at the Zoological Survey of India, Calcutta, and it could not be examined. Nevertheless, different specimens agree well with the definition of the two species as given by Alcock as well as with the differences shown in his illustrations so that the two species are regarded here as clearly distinct.

Examination of most of the specimens identified as E. desciscens by Chen (1985: 197; 1993: 337; 1998: 234; 2000: 427) revealed that they do not agree with Alcock’s descriptions ( Alcock 1896: 286; 1899: 35) and illustrations ( Alcock & MacGilchrist 1905: pl. 72, fig. 2, 2a) of E. desciscens but that they belong instead to two species, E. robusta ( Miers, 1886) , and E. chenae Ng & Ho, 2003 (see synonymy above). Some of her material could not be examined, however, but Chen’s figures of E. desciscens from the East China Sea ( Chen 1986: fig. 15; Chen & Sun 2002: fig. 108) indicate that her material most probably belongs to a third species, E. taiwanensis Ng & Ho, 2003 , a view previously expressed by Ng & Ho (2002: 74).

The Madagascar specimens identified as E. desciscens by Chan (1987) have close similarities to E. robusta in terms of the shape of the carapace and eyes, and are more unlike the specimen of E. desciscens illustrated by Alcock & MacGilchrist (1905: pl. 72, fig. 2, 2a). The outer orbital teeth of these specimens are slightly longer than those of E. robusta , although this is a variable character in this last species. The G1 and G2 of a Madagascar male ( Fig. 20 ) are characteristic enough, however, to consider the Madagascar specimens different from E. robusta ( Fig. 25B, C ). The examination of the type material of E. desciscens and its comparison with those of E. investigatoris and E. robusta should shed light on the status of these species. Alcock’s material of the first two species, however, was unavailable.

Figures

FIG. 19. — Ethusina coronata n. sp., holotype cl 12.1 mm, cw 12.0 mm, Solomon Islands, Indispensable Strait west of Malaita, SOLOMON 1, stn CP 1764, 1327-1598 m (MNHN-B 28734); A, dorsal surface of carapace and P2; B, right G1, ventrolateral (left) and dorsal (right) views. Scale bars: A, 5 mm; B, 1 mm.

FIG. 34. — Bathymetric distribution of Indo-West Pacific ethusine crabs.

FIG. 25. — Ethusina robusta (Miers, 1886); A, lectotype cl 10.0 mm, cw 10.1 mm, Challenger, stn 191, Arafura Sea, 1463 m (BMNH 84.44), dorsal surface of carapace and P2; B, C, cl 8.6 mm, cw 8.2 mm, Solomon Islands, east of Malaita, SALOMON 1, stn CP 1764, 1327-1598 m (MNHN-B 28712); B, left G1, dorsal view; C, left G2, dorsal view. Scale bars: A, 5 mm; B, C, 1 mm.

FIG. 20. — Ethusina desciscens (Alcock, 1896), cl 7.2 mm, cw 7.4 mm, Madagascar, off northwest coast, Vauban, stn CH 142, 1250-1300 m (MNHN-B 18277); A, left G1, dorsal view; B, left G2, ventral view. Scale bars: 1 mm.

FIG. 2. — Ethusa abbreviata n. sp., holotype cl 13.8 mm, cw 14.5 mm, Vanuatu, N of Espiritu Santo, MUSORSTOM 8, stn CP 1124, 532-599 m (MNHN-B 27505); A, dorsal surface of carapace; B, ventral view of anterior portion of body; C, left G1, dorsal views; D, left G2, dorsal view. Scale bars: A, 5 mm; B-D, 2 mm.