Ethusa, Roux, 1830

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 : 507-509

KEY TO INDO- WEST PACIFIC SPECIES OF ETHUSA

1. Anterior border of endostome extends below level of posterior (lower) border of antennular fossae of basal antennular articles, or at most, reaches posterior border of antennular fossae ( Fig. 1B ) .................................................................................... 2

— Anterior border of endostome extends above (beyond) posterior (lower) border of antennular fossae of basal antennular articles ...................................................... 24

2. Outer orbital teeth reaching higher or almost as high as lateral frontal teeth (at least 3/4 or more height of inner margin of orbital sinus) .............................................. 3

— Outer orbital teeth clearly not as high as lateral frontal teeth, only reaching 3/4 or less height of inner margin of orbital sinus .......................................................... 14

3. Outer orbital teeth reaching higher than frontal teeth; if equal or even slightly short- er than frontal teeth, outer orbital teeth slender (not triangular), horn-like, directed outwardly .............................................................................................................. 4

— Outer orbital teeth nearly as long (at least 3/4 height of inner margin of orbital sinus) as frontal teeth ............................................................................................ 5

4. Outer orbital teeth slender, acute, conspicuously directed outwardly ( Fig. 33C ; Chen 1985: figs 8, 9b). Orbital sinuses broad, U-shaped. Typically large-size (cl 15 mm or more) .................................................................................. E. indica

— Outer orbital teeth narrowly triangular, may be slightly directed outwardly ( Chen 1993: fig. 2a, b). Orbital sinuses V-shaped. Known only from small (max cl 7.3 mm) individuals .............................................................................................. E. crosnieri

5. Dorsal surface of carapace, P2-P5 covered by varying amounts of hair (particularly conspicuous along anterior, anterolateral borders) or long tomentum (hair may be covered by sediment) ............................................................................................ 6

— Dorsal surface of carapace naked or only covered by short, sparse setae ................ 7

6. P4, P5 long, slender, with slender dactyli ( Chen 1985: fig. 13). Outer orbital teeth typically directed inwardly. Dorsal surface of carapace with coarse granules .............. .................................................................................................................... E. foresti

— P4, P5 relatively short, with short, thick dactyli ( Chen 1985: fig. 11; Chen & Sun 2002: fig. 103.1). Outer orbital teeth typically directed outwardly. Dorsal surface of carapace with fine granules, varying amounts of hair ................................ E. izuensis 7. Carapace with lateral borders that are almost parallel to each other, diverging toward posterior border without conspicuous widening of posterior portion ........ 8

— Carapace with lateral borders that diverge toward posterior border by forming noticeable or conspicuous enlargement of carapace on posterior portion, often pearshaped in appearance ( Fig. 2 ) ............................................................................ 12

8. Outer orbital teeth not reaching height of frontal teeth; always slender, being longer than wide, slightly oriented outwardly. Western Indian Ocean in distribution .... 9

— Outer orbital teeth typically reaching height of frontal teeth (or are slightly shorter than frontal teeth); typically (but not exclusively) triangular, being as long as wide at base. Western Pacific Ocean in distribution .................................................. 10

9. G1 each with broad, thick distal end (Chen 1987: fig. 5e) .................. E. sinespina

— G1 each with slender distal end ( Fig. 15 ; Chen 1987: fig. 3e, as E. madagascariensis Chen, 1987 ) .................................................................................... E. zurstrasseni

10. G1 stout, each with attenuated distal end ( Chen 1993: fig. 5f-h) ........ E. granulosa

— G1 slender, each with pointed distal end .......................................................... 11

11. Distal end of each G1 with conspicuous notch ( Chen 1993: fig. 7e) ...................... ...................................................................................................... E. magnipalmata

— Distal end of each G1 smooth, without notch ( Fig. 14B ) .................... E. orientalis

12. Outer orbital teeth oriented slightly outward, slender, narrow, acute tip ................ .................................................................................................... E. machaera n. sp.

— Outer orbital teeth straight, triangular, proximal width being approximately equal to height ............................................................................................................ 13

13. Lateral frontal sinuses U-shaped, nearly symmetrical, outer margins (inner margins of outer orbital teeth) straight ( Fig. 2A ; Chen 1985: fig. 5, as E. sexdentata ( Stimpson, 1858)) .................................................................... E. abbreviata n. sp.

— Lateral frontal sinuses V-shaped, asymmetrical, outer margins (inner margins of outer orbital teeth) conspicuously swollen ( Sakai 1937: fig. 1a; 1965: pl. 11, fig. 2; 1976: fig. 26a; Chen 1993: fig. 14a) .................................................. E. sexdentata

14. Outer orbital teeth very short, less than 1/4 height of inner margin of orbital sinus ............................................................................................................................ 15

— Outer orbital teeth not reaching frontal teeth but more than 1/4 height of inner margin of orbital sinus ...................................................................................... 18

15. Outer orbital teeth located at outer margins of deep, V-shaped orbital sinuses. Carapace with lateral margins that strongly diverge toward posterior border, forming noticeable enlargement of posterior portion, pear-shaped in appearance ( Sakai 1983b: fig. 1a) .............................................................................. E. philippinensis

— Outer orbital teeth located at outer margins of L-shaped orbital sinuses. Carapace with parallel or near-parallel sides, square or rectangular in appearance .............. 16

16. Frontal border with only two (lateral frontal) teeth and two median frontal lobes ( Chen 1993: fig. 4a) .................................................................................. E. furca

— Frontal border with four teeth (two lateral frontal and two median frontal) ...... 17

17. Median frontal teeth reaching much higher than lateral frontal teeth; median frontal sinus much wider than lateral frontal sinuses ( Fig. 9 ); outer orbital teeth very small, straight, not directed laterally ................................................ E. hawaiiensis

— Median frontal teeth almost as high as lateral frontal teeth; median frontal sinus slightly wider than lateral frontal sinuses ( Sakai 1937: fig. 1c; 1976: fig. 26c; Chen 1985: fig. 10a); outer orbital teeth conspicuous, directed outwardly .... E. quadrata

18. Lateral frontal teeth oriented outwardly ( Chen 1997: fig. 4a); inner margins of outer orbital teeth (outer margins of orbital sinuses) sinuous, not straight, often making tips conspicuously narrower than rest of teeth .................... E. indonesiensis

— Lateral frontal teeth straight; inner margins of outer orbital teeth (outer margins of orbital sinuses) straight or J-shaped, not sinuous, so that tip not conspicuously constricted ........................................................................................................ 19

19. Orbital sinuses broad, U-shaped (Sakai 1977: fig. 1b; 1976: fig. 26b; Chen 1985: fig. 7a) .............................................................................................. E. latidactyla

— Orbital sinuses V-shaped .................................................................................. 20

20. Outer orbital teeth straight ( Chen 1997: fig. 3a) ................................ E. dilatidens

— Outer orbital teeth directed outwardly .............................................................. 21

21. P2, P3 relatively short, thick ( Fig. 6A ) ...................................... E. crassipodia n. sp.

— P2, P3 slender, not conspicuously thick ............................................................ 22

22. G1 conspicuously bent or curved ( Chen 1993: fig. 3e) .......................... E. curvipes

— G1 straight or only slightly sinuous .................................................................... 23

23. G1 each with small, slightly pointed tubercle at base of distal end ( Chen 1993: fig. 13f) ................................................................................................ E. pygmaea

— G1 each with conspicuous, rounded tubercle at base of distal end, giving pleopods foot-like appearance ( Chen 1993: fig. 12e) .................................... E. parapygmaea

24. Outer orbital teeth straight ................................................................................ 25

— Outer orbital teeth not straight, directed outwardly or inwardly ........................ 27

25. Outer orbital teeth slender; orbital sinuses wide, U-shaped ( Chen 1993: fig. 9a, as E. makasarica Chen, 1993 ) ...................................................................... E. hirsuta

— Outer orbital teeth triangular; orbital sinuses narrow, V-shaped ........................ 26

26. Dorsal surface of carapace covered by very conspicuous, long hairs ( Fig. 5A ); carapace with lateral borders that diverge toward posterior border ...... E. barbata n. sp.

— Dorsal surface of carapace without conspicuous, long hairs; carapace with lateral borders that are nearly parallel to each other ( Fig. 4 ) ...................... E. andamanica

27. Outer orbital teeth directed inwardly ( Chen 1993: fig. 11a, b) ........ E. obliquidens

— Outer orbital teeth directed outwardly .............................................................. 28

28. Orbital sinuses U-shaped. Surface, margins of carapace with conspicuous granules ( Chen 1997: fig. 5a, m) .................................................................. E. longidentata

— Orbital sinuses V-shaped ( Sakai 1937: fig. 1e; 1965: pl. 11, fig. 2; 1976: fig. 26e; Chen 1993: fig. 10a). Surface of carapace with small granules ................ E. minuta

Figures

FIG. 1. — Terminology used to describe the carapace of members of the subfamily Ethusinae; A, dorsal surface of the carapace; B, ventral view of anterior portion of the body.

FIG. 33. — A, Ethusa granulosa Ihle, 1916, cl 14.7 mm, cw 14.6 mm, Vanuatu, west coast of Malekula, MUSORSTOM 8, stn DW 1061, 458-512 m (MNHN-B 28698) (photograph by J.-L. Menou, IRD, Nouméa); B, Ethusa hawaiiensis Rathbun, 1906, cl 6.7 mm, cw 6.2 mm, Vanuatu, S of Anatom, MUSORSTOM 8, stn CP 963, 400-440 m (MNHN-B 28538) (photograph by J.-L. Menou, IRD, Nouméa); C, Ethusa indica Alcock, 1894, cl 7.8 mm, cw 7.8 mm, Vanuatu, SE of Éfaté, MUSORSTOM 8, stn CP 1036, 920-950 m (MNHN-B 28560) (photograph by J.-L. Menou, IRD, Nouméa); D, Ethusina challengeri (Miers, 1886), cl 25.9 mm, Mid-Indian Basin, SAFARI 2, stn 35, trawl CP 29, 4950-4928 m (MNHN-B 28697) (photograph by P. Briand, IFREMER); E, Ethusina macrospina Ng & Ho, 2003, cl 10.4 mm, cw 11.0 mm, Taiwan, off southwest coast, TAIWAN 2003, stn CD 203, 635-868 m (NTOU) (photograph by T.-Y. Chan, NTOU).

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.

FIG. 15. — Ethusa zurstrasseni Doflein, 1904, holotype cl 7.2 mm, cw 6.8 mm, southern Somalia, Deutsche Tiefsee Expedition, Valdivia, stn 254, 977 m (ZMB 13629), right G1, distal part, ventrolateral (left) and dorsolateral (right) views. Scale bar: 1 mm.

FIG. 14. — Ethusa orientalis Miers, 1886, lectotype cl 15.7 mm, cw 15.1 mm, Fiji, E of Kadavu, Challenger, stn 173A, 567 m (BMNH 84-44); A, dorsal surface of carapace; B, left G1, ventral (left) and dorsal (right) views; C, right G2, dorsal view. Scale bars: A, 3 mm; B, C, 2 mm.

FIG. 9. — Ethusa hawaiiensis Rathbun, 1906, cl 4.9 mm, cw 4.2 mm, French Polynesia, Marquesas Islands, Ua Pou, MUSORSTOM 9, stn DW 1146, 200 m (MNHN-B 28552).

FIG. 6. — Ethusa crassipodia n. sp., paratype cl 9.3 mm, cw 8.9 mm, Solomon Islands, E of Malaita, SALOMON 1, stn CP 1783, 399-700 m (MNHN-B 28701); A, dorsal surface of carapace and P2; B, ventral view of anterior portion of body; C, left G2, ventral view; D, left G1, dorsal (left) and ventral (right) views. Scale bars: A, 5 mm; B, 2 mm; C, D, 1 mm.

FIG. 5. — Ethusa barbata n. sp., juv. holotype cl 6.8 mm, cw 6.9 mm, Solomon Islands, N of Guadalcanal, SALOMON 1, stn CP 1804, 309-328 m (MNHN-B 28707); A, frontolateral portion of dorsal surface of carapace, most setae removed along right anterior margin; B, ventral view of anterior portion of carapace. Scale bars: A, 1 mm; B, 2 mm.

FIG. 4. — Ethusa andamanica Alcock, 1894, juv. “type” cl 6.8 mm, cw 7.1 mm, Andaman Sea off Andaman Islands, Investigator, stn 238, 110-137 m (BMNH 1939.9.20.10), dorsal surface of carapace. Scale bar: 5 mm.