Ethusina robusta ( Miers, 1886 )

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 : 570-575

Ethusina robusta ( Miers, 1886)

( Figs 22 ; 25 )

Ethusa (Ethusina) gracilipes var. robusta Miers, 1886 : xxvii, 333, pl. 29, fig. 2.

Ethusa (Ethusina) investigatoris Alcock, 1896: 285 ; 1899: 34.

Ethusa investigatoris – Alcock & MacGilchrist 1905: pl. 72, fig. 3, 3a.

Ethusina investigatoris – Doflein 1904: 292 (list), fig. 65. — Ihle 1916b: 146, 151 (list), 153 (list), 156 (list).

Ethusina gracilipes – Ihle 1916b: 146, 151 (list) (part), 152 (list), 153 (list) (part), 156 (list) (part) (not E. gracilipes ( Miers, 1886)) .

? Ethusa investigatoris – Menon 1937: 37, figs 166-201.

Ethusa gracilipes robusta – Serène 1968: 40 (list).

Not Ethusa robusta – Chen 1986: 133, fig. 13 (= E. chenae Ng & Ho, 2003 ).

Ethusina investigatoris – Serène 1968: 40 (list). — Chen 1986: 135, fig. 14; 1997: 624. — Chen & Xu 1991: 60, fig. 9. — Chen & Sun 2002: 54, 250, fig. 107, pl. 9, fig. 5. — Ng & Ho 2003: 72 (list).

? Ethusa aff. investigatoris – Serène & Vadon 1981: 119, 121.

Not Ethusina robusta – Manning & Holthuis 1981: fig. 9b. — Wicksten 1989: 316. — Hendrickx 1995: 128; 1997: 76, fig. 65 (= Ethusina sp. ).

Ethusina desciscens – Chen 1993: 336 (key), 337; 1997: 624; 2000: 427 (not E. desciscens ( Alcock, 1896)) .

Ethusina investigator [sic] – Chen 1993: 336 (key).

Not Ethusina robusta – Chen 1993: 336 (key), 342 (= E. macrospina Ng & Ho, 2003 ; = E. stenommata n. sp.; = E. vanuatuensis Chen, 1993 ); 2000: 430 (= E. ciliacirrata n. sp.; = E. coronata n. sp.; = E. vanuatuensis Chen, 1993 ), fig. 3 (= E. coronata n. sp.). — Chen & Sun 2002: 54, 248, fig. 106 (= E. chenae Ng & Ho, 2003 ).

Ethusina robusta – Ng & Ho 2003: 72 (list).

Ethusina alcocki Ng & Ho, 2003: 74 , figs 4, 5.

? Ethusina robusta – Marumura & Kosaka 2003: 23.

TYPE MATERIAL. — Lectotype of Ethusina robusta ( Miers, 1886) : cl 10.0 mm, cw 10.1 mm, Challenger, stn 191 ( BMNH 84.44 ); paralectotypes: cl 15.2 mm, cw 15.6 mm, Challenger, stn 195 ( BMNH 84.44 ), cl 10.1 mm, cw 10.2 mm, cl 10.6 mm, cw 10.9 mm, Challenger, stn 191 ( BMNH 84.44 ).

Miers (1886) based his description on four female specimens without selecting a holotype. One of the four syntypes, the most complete of the three smaller females, is hereby designated the lectotype and the remaining three specimens are the paralectotypes.

Type material of Ethusina investigatoris ( Alcock, 1896) : unknown (Zoological Survey of India, Calcutta?).

Type material of Ethusina alcocki Ng & Ho, 2003 : holotype: cl 8.4 mm, cw 8.6 mm, TAIWAN 2000, stn CP 32 ( NTOU).

TYPE LOCALITY. — Arafura Sea, 05°41’S, 134°04.5’E, 1463 m.

MATERIAL EXAMINED. — Taiwan. TAIWAN 2000, stn CP 23, 22°11.9’N, 120°02. 9’E, 876 m, 29.VII. 2000, 1 parasitized by Sacculina sp. ( MNHN-B 28826). — Stn CP 32, 22°01.7’N, 120°11.1’E, 910-1129 m, 30.VII.2000, 1 holotype of E. alcocki (NTOU) .

TAIWAN 2002, stn CP 189, 21°39.91’N, 118°20.94’E, 1649- 1629 m, 27.VIII.2002, 1 ( NTOU). — Stn CP 190, 21°35.01’N, 118°15.02’E, 1650-1665 m, 28.VIII.2002, 1 ( NTOU).

TAIWAN 2003, stn CD 226, 22°19.15’N, 121°04.63’E, 1171-1212 m, 29.VIII.2003, 1 ( NTOU).

Indonesia. Makassar Strait, CORINDON 2, stn 220, 00°13.6’N, 118°12.3’E, 2350 m, 2.XI.1980, 1 ( MNHN-B 19077). — Stn 231, 00°04. 9’N, 119°47.8’E, 1080- 980 m, 4.XI.1980, 2 ( MNHN-B 19070).

Lesser Sunda Islands, Siboga , stn 48, off eastern tip of Sumbawa island, Bali Sea, 08°04.7’S, 118°44.3’E, 2060 m, 13.IV.1899, 1 ( ZMA Crust.De. 241702). Celebes, Siboga , stn 211, N of northern tip of Selayar island, southern Celebes, 05°40.7’S, 120°45.5’E, 1158 m, 25.IX.1899, 1 ( ZMA Crust.De. 241689).? Siboga , stn 208, S of Buna island, 05°39’S, 122°12’E, 1886 m, 22.IX.1899, 1 ( ZMA Crust.De 241709).

Banda Sea, Challenger, stn 195, 04°21’S, 129°07’E, 2624 m, 3.X.1874, 1 paralectotype ( BMNH 84.44).

Tanimbar Islands, KARUBAR, stn CP 53, 08°18’S, 131°41’E, 1026-1053 m, 30.X.1991, 1 ( MNHN-B 22876). — Stn CP 87, 08°47’S, 130°49’E, 1017- 1024 m, 5.XI.1991, 1 ( MNHN-B 22883), 1 ( MNHN-B 22875). — Stn CP 89, 08°39’S, 131°08’E, 1084- 1058 m, 5.XI.1991, 3 ovig.

( MNHN-B 22877).

Arafura Sea, Challenger, stn 191, 05°41’S, 134°04.5’E, 1463 m, 23.IX.1874, 1 lectotype, 2 paralectotypes ( BMNH 84.44).

Solomon Islands. SALOMON 1, stn CP 1764, 08°36.6’S, 160°07.4’E, 1327-1598 m, 27.IX.2001, 1 ( MNHN-B 28712).

Vanuatu. MUSORSTOM 8, stn CP 1109, 14°52.20’S, 167°18.00’E, 1550-1620 m, 8.X.1994, 1 ( MNHN-B 27509).

New Caledonia. BATHUS 3, stn CP 844, 23°06’S, 166°46’E, 908 m, 1.XII.1993, 1 ( MNHN-B 28528).

Fiji. MUSORSTOM 10, stn CP 1353, 17°30.9’S, 178°53.3’E, 879-897 m, 12.VIII. 1998, 1 ( MNHN-B 28673). — Stn CP 1354, 17°42.6’S, 178°55.0’E, 959-963 m, 12.VIII. 1998, 1 ( MNHN-B 28671). — Stn CP 1361, 18°00.0’S, 178°53.7’E, 1058-1091 m, 13.VIII.1998, 3 ( MNHN-B 28672).

BORDAU 1, stn CP 1458, 17°22’S, 179°28’W, 1216-1226 m, 5.III.1999, 3 ( MNHN-B 28670). DISTRIBUTION. — Known from Eastern and Western India ( Alcock 1896, as Ethusa investigatoris ( Alcock, 1896)) , East China Sea ( Chen 1986, as Ethusina investigatoris ), Taiwan ( Ng & Ho 2003, as Ethusina alcocki Ng & Ho, 2003 ), South China Sea ( Chen & Xu 1991, as Ethusina investigatoris ), Indonesia: Makassar Strait ( Chen 1993, as Ethusina desciscens ( Alcock, 1896)) , Lesser Sunda Is and Celebes ( Ihle 1916b, as Ethusina gracilipes ( Miers, 1886) and Ethusina investigatoris ), Tanimbar Is ( Chen 1997, as Ethusina desciscens and E. investigatoris ), and Banda and Arafura seas ( Miers 1886), Vanuatu ( Chen 2000, as Ethusina desciscens ), and now from the Solomon Is, New Caledonia, and Fiji ( Fig. 22 ). Depth: 876-2624 m ( Fig. 34 ).

SIZE. — Maximum size: cl 10.9 mm, cw 11.0 mm ( ZMA Crust.De 241709), cl 15.2 mm, cw 15.6 mm ( BMNH 84.44).

REMARKS

Ethusina robusta was described from four females as Ethusa (Ethusina) gracilipes var. robusta Miers, 1886 , a “variety” of Ethusa (Ethusina) gracilipes Miers, 1886 . The variety was distinguished by having: 1) “more dilated bases of the antennules”; 2) “the slightly tapering, not cylindrical [i.e. not flattened] eye-peduncles”; and 3) “the more robust chelipedes and ambulatory legs” ( Miers 1886: 333). These three differences are clearly shown in Miers’ figures ( Miers 1886: pl. 29). The examination of the type materials of both Ethusina gracilipes and its purported variety showed that these are clearly species-level differences. These and additional differences between E. robusta and E. gracilipes are further analyzed in the discussion of E. gracilipes (see above).

Of the four females studied by Miers, the most complete specimen ( Fig. 25A ; cl 10.0 mm, cw 10.1 mm, BMNH 84.44) has been designated the lectotype; a large female (cl 15.2 mm, cw 15.6 mm, BMNH 84.44), which was illustrated by Miers (1886: pl. 29, fig. 2), and the two remaining small females are the paralectotypes (see Type material above). The outer orbital and frontal teeth of the large female paralectotype were unfortunately severed and/or were worn out. As a result, the outer orbital teeth are shown in Miers’ figure as short and triangular rather than long and needle-like as in the other smaller females in the type material ( Fig. 25A ). Much confusion has resulted from the use of Miers’ illustration of this atypical, large specimen as a reference for E. robusta . Further sources of confusion have been the misinterpretation of Miers’ comparison with E. gracilipes and his use of the name “robusta” to imply that thick, short pereopods are diagnostic to E. robusta . More importantly, no investigators after Miers appear to have examined the type material, which also includes the three more typical females. The description of males and females of E. robusta as different species as a result of sexual dimorphism was an additional source of confusion.

Ambiguity about the identity of Miers’ species has led to numerous misidentifications and the description of two separate species: E. investigatoris ( Alcock, 1896) , and E. alcocki Ng & Ho, 2003 . Specimens referred to these two species show the diagnostic characters of E. robusta : very slender, needle-like, dorsally-directed outer orbital teeth that reach (and sometimes go beyond) the frontal teeth, slender P2 and P3, relatively long eye peduncles that, often in males and very rarely in females, are visible beyond the outer margins of the outer orbital teeth (as a result of a narrower carapace in contrast to the more inflated carapace of females), and characteristic, stout, nearly symmetrical G1.

Ethusina investigatoris was described by Alcock (1896: 286) from the Bay of Bengal and the Laccadive Sea. In its description Alcock stated that his new species “may possibly be only a variety of Ethusa (Ethusina) gracilipes, Miers ”. Alcock (1899: 35), however, distinguished E. investigatoris from E. gracilipes by the presence in E. investigatoris of: 1) a transverse “groove or crease” in the form of a flattened region along the anterior portion of the carapace (clearly visible in Alcock & M a c G i l c h r i s t 1 9 0 5: p l. 7 2, f i g. 3); a n d 2) longer eye peduncles, which allow the eyes to be typically visible beyond the outer margins of the outer orbital teeth and certainly above the lower margin of the orbital sinuses ( Alcock 1899: 35; Alcock & MacGilchrist 1905: pl. 72, fig. 3, 3a). Also characteristic and clearly visible in Alcock & MacGilchrist’s figure is the presence of a narrow, vertical depression that extends from the posterior edge of the median frontal sinus to the flattened region along the anterior portion of the carapace, thus clearly demarcating the anteri- or portion of the carapace into two lobed regions. Alcock (1896: 285) also added in his description that each outer orbital tooth is “long and needlelike, but its teeth falls considerably short of the tips of the rather acute frontal spines” ( Alcock & MacGilchrist 1905: pl. 72, fig. 3, 3a). The relative lengths of the outer orbital teeth, however, have been found to vary with body size.

The eye peduncles of E. investigatoris are long, indeed markedly longer than in E. desciscens ( Alcock, 1896) , a close species from the Indian Ocean, as illustrated by Alcock & MacGilchrist (1905: pl. 72, fig. 3a for E. investigatoris , fig. 2a for E. desciscens ). Alcock (1896: 286) described E. desciscens as a possible “variety” of E. investigatoris but the two are clearly different species (see Remarks of E. desciscens above).

Alcock’s description of E. investigatoris was based only on male specimens and all of the specimens that were eventually identified and recorded in the literature that agree with Alcock’s description and figures happen to be males. Although the type material of E. investigatoris , supposedly at the Zoological Survey of India in Calcutta, is unavailable, numerous male specimens from Taiwan, Indonesia, the Solomon Is, Vanuatu, New Caledonia, and Fiji agree with its description and figures by Alcock ( Alcock 1896; Alcock & MacGilchrist 1905). Although there was no actual “groove” demarcating the anterior border from the rest of the carapace, there was a clear flat border between the bilobed anterior border and the remaining, arched posterior portion of the carapace. The eye peduncles were always long in these specimens. The P2 and P3 were similarly long and slender.

The re-examination of the material (all males) previously identified as E. investigatoris s.s. by Ihle (1916b) and Chen (1997) has shown that they are E. robusta ( Miers, 1886) . Similarly, a male from the South China Sea originally identified as E. investigatoris by Chen was found by Ng & Ho (2003: 75) to be conspecific with E. alcocki Ng & Ho, 2003 , a junior subjective synonym of E. robusta . The Chinese material described by Chen (1986: fig. 14), Chen & Xu (1991: fig. 9), and Chen & Sun (2002: fig. 107) as E. investigatoris has yet to be re-examined (see Ng & Ho 2003: 75) but the figures (all of males) indicate the diagnostic characters of E. robusta .

The shape of the outer orbital and frontal teeth of E. robusta and E. investigatoris are practically identical, except that the outer orbital teeth are shorter in male E. investigatoris . Only male specimens of E. investigatoris could be distinguished from female specimens of E. robusta , and male specimens sharing the diagnostic characteristic of female E. robusta were yet to be found. The flat area between the anterior portion and the rest of the carapace, the bilobed character of the anterior portion of the carapace, and eye peduncles that are long and visible beyond the outer margins of the outer orbital teeth, the diagnostic characters of E. investigatoris , are indeed those characters that distinguish female from male E. robusta . E. investigatoris ( Alcock, 1896) is therefore a junior subjective synonym of E. robusta ( Miers, 1886) , and the differences between the two are the result of sexual dimorphism in E. robusta .

A similar sexual dimorphism in the shape of the carapace is observed in E. paralongipes Chen, 1993 (see Remarks of this species above). Indeed, males of E. paralongipes can be easily confused with males of E. robusta since both species share long outwardly directed outer orbital teeth. Males and females of both species can be separat- ed by the presence of unusually long P2 and P3 (1.1-1.2 times carapace length) in E. paralongipes , much longer than in E. robusta .

A large male collected by the Siboga expedition in Indonesia (cl 10.9 mm, cw 11.0 mm, ZMA Crust.De 241709) and identified as E. investigatoris by Ihle (1916b: 146) is cautiously referred to E. robusta . Its eyes were barely visible dorsally, although this may be the result of the larger carapace of the specimen. The G1, however, were clearly stouter and wider at the tip like those of E. robusta ( Fig. 25B ). A female from the same Siboga collection clearly belongs to E. robusta ; two other specimens are not extant. A male specimen from the Philippine Is identified as Ethusa aff. investigatoris by Serène & Vadon (1981) is missing from the MNHN collection so its identity could not be verified.

The two of the five specimens from Indonesia described by Ihle (1916b) as E. gracilipes that are extant (cl 4.0 mm, cw 4.1 mm, ZMA Crust.De. 241689;, ZMA Crust.De. 241702) were found to belong to E. robusta . They have much shorter eye peduncles than Miers’ type material of E. gracilipes , which allow the eyes to be barely seen dorsally ( Ihle 1916b: fig. 77), and much narrower (V-shaped rather than U-shaped) orbital sinuses. Chen (1985: 197) identified Ihle’s specimens as E. desciscens apparently based only on Ihle’s figure since there is no mention of an examination of Ihle’s material at ZMA. Indeed, neither Ihle’s nor Chen’s figures ( Chen 1985: fig. 15) conform to Alcock’s figure of E. desciscens ( Alcock & MacGilchrist 1905: pl. 72, fig. 2, 2a), nor there is mention of the examination of Alcock’s type material by either Ihle or Chen.

Two females, one from Taiwan and a second from the South China Sea, originally described as a new species, E. alcocki Ng & Ho, 2003 , are conspecific with E. robusta . Ng & Ho (2003: 75) agreed that their new species was close to E. investigatoris but opted to describe it as new based on three differences observed when comparing their two female s p e c i m e n s w i t h A l c o c k ’s f i g u r e s (A l c o c k & MacGilchrist 1905: pl. 72, fig. 3). Their specimens showed less prominent median frontal teeth, a relatively wider supraorbital margin, and P2 and P3 dactyli “about one-third” longer and narrower than in the male of E. investigatoris figured by Alcock. These characters are clearly the result of individual variation and sexual dimorphism. One major difference between their type material and Alcock’s figures, the much longer eye peduncles of Alcock’s male, remained nevertheless unnoticed. Ng & Ho, however, correctly recognized that specimens previously identified by Chen as E. investigatoris belong to their new species. Four additional specimens of E. robusta , three females and one male, have been identified from Taiwan since the description of E. alcocki .

The G1 of E. robusta ( Fig. 25B ; Chen 1986: fig. 14.70; Chen & Xu 1991: fig. 9; Chen & Sun 2002: fig. 107.5, all as E. investigatoris ) are relatively stout, dorsoventrally flattened, nearly symmetrical, and with slightly pointed tips. The distal ends of the G2 ( Fig. 25C ) are pointed.

The identity of a specimen of E. robusta from Japan ( Marumura & Kosaka 2003) needs to be verified. The status of specimens from the Eastern Pacific region referred to as E. robusta remains questionable. Rathbun (1906) synonymized Ethusina gracilipes with E. gracilipes var. robusta . The specimen from the Galápagos Is illustrated by Hendrickx (1997: fig 65) is definitely not E. robusta and it does not appear to be an Indo- West Pacific species. The eyes are not visible dorsally and the teeth along the anterior border of the carapace are much longer than in E. robusta . This Eastern Pacific species has been reported from Baja California to Ecuador ( Hendrickx 1997: 76).

Material from the Eastern Pacific previously synonymyzed with E. gracilipes by Rathbun (1937: 94) was referred to as E. robusta by Wicksten (1989: 316) and Hendrickx (1995: 128; 1997: 76). A photograph of a female specimen from the Galápagos Is ( Rathbun 1937: pl. 30, fig. 4, pl. 31, fig. 4, as E. gracilipes ) and a line drawing of a male from the same location (Henrickx 1997: fig. 65) demonstrate that the specimens do not belong to Miers’s species. Although there are similarities in the shape and relative size of the outer orbital and frontal teeth (longer in the male, however), the P2 and P 3 in the photographed specimen are short and thick. The Galapagos Is specimens may belong to an undescribed Eastern Pacific endemic. Manning & Holthuis (1981: fig. 9b) illustrate the tip of the G1 from a specimen referred to as E. robusta and collected from the Galápagos Is. It presumably belongs to the material similarly identified by Rathbun from the same area. Its shape, however, is different from that of the Indo-West Pacific E. robusta ( Miers, 1886) .

Figures

FIG. 22. — Geographical distribution of Ethusina gracilipes (Miers, 1886) (G) and Ethusina robusta (Miers, 1886) (●).

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