Ethusina chenae Ng and Ho, 2003

(Fig. 4)

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 26 (Timor Sea; 09°27.0′S, 127°58.6′E –09°285.0′S, 127°56.1′E, 610–690 m deep), 3 m beam trawl; 19 June, 1972; 1 juv. (NSMT-Cr 29256: CB 4.0 mm, CL 4.2 mm), 1 juv. (NSMT-Cr 29257, dried up: CB 5.0 mm, CL 5.5 mm), 1 ♀ (NSMT-Cr 29255: CB 9.3 mm, CL 10.9 mm).

Remarks. Ethusina robusta (Miers, 1886), E. investigatoris (Alcock, 1896), E. desciscens (Alcock, 1896), E. vanuatuensis Chen, 2000, and E. alcocki Ng and Ho, 2003 are closely related, differing from each other mainly in details of the front-orbital tuberculation. Their complex synonymies were thoroughly clarified by Castro (2005): 1) Ethusina investigatoris and E. alcocki were synonymized with E. robusta; 2) Ethusina robusta identified by Chen (1986) was corrected to E. chenae Ng and Ho, 2003; 3) the identifications of E. desciscens identified by Chen (1986, 1998), and Chen and Sun (2002) were corrected to E. taiwanensis Ng and Ho, 2003; 4) Ethusina robusta identified by Chen (1993) was referred to E. vanuatuensis Chen, 1993, E. macrospina Ng and Ho, 2003, and E. stenommata Castro, 2005; 5) Ethusina robusta identified by Chen (2000) was reidentified as E. ciliacirrata Castro, 2005, and E. coronata Castro, 2005; and 6) the identification of E. robusta by Chen and Sun (2002) was similarly corrected to E. chenae Ng and Ho, 2003.

After detailed comparison with the literature, the female at hand (Fig. 4A–B), which is fully mature, was identified with E. chenae. Among the species mentioned above, E. chenae is characteristic in that 1) the carapace shape is not constricted behind the external orbital spine that is directed nearly forward or only slightly outward, with the tip reaching nearly to the tip of the median frontal tooth, 2) each median frontal tooth is triangular in dorsal view, with a sharp tip, and the lateral frontal tooth is directed forward, similar in shape to the outer orbital spine, extending beyond the tip of the median frontal tooth, 3) the median frontal sinus is comparatively wide and shallow, and the orbital sinus is distinctly shallow, with the orbital margin gently retreating toward the external orbital spine. The characters observed as above in the present female seem to be minor but reliable, agreeing well with the original description and figures by Ng and Ho (2003), and with comments by Castro (2005). In the holotype female, both of the median frontal teeth seem to be blunt, probably due to damage during lifetime. The figures represented by Chen and Sun (2002) as E. robusta are somewhat schematic, but indicative of the specific characters of E. chenae.

Two small juveniles at hand belong without doubt to Ethusina by having the swollen basal antennular article pushing the antenna and the long ambulatory legs, but it is remarkable in having the prominent eyestalks visible from above, different from most of the congeners and somewhat similar to the Ethusa species. They keyed out close to E. desciscens in the key provided by Castro (2005). The semitransparent soft carapace, with sharp but not spiniform frontal and external orbital teeth, and the distinct eyestalks may be referable to the immaturity of the specimens.

Distribution. East China Sea (Chen, 1986, as E. robusta), Taiwan (Ng and Ho, 2002; Castro, 2005), the Philippines (Chen, 1985, as E. desciscens; Castro 2005), 509–1649 m depth. The record of E. desciscens from Japan by Marumura and Kosaka (2003) is not yet verified.