Ethusa machaera, 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 : 534-536

Ethusa machaera n. sp.

( Fig. 13 )

Ethusa hirsuta – Chen 1987: 685, pl. 1, fig. F; 1993: 318 (key), 319 (list) (part) (not E. hirsuta McArdle, 1900 ).

TYPE MATERIAL. — Holotype: cl 11. 0 mm, cw 11.7 mm, Vauban , stn CH 94 ( MNHN-B 18274 ); paratypes: other two specimens listed under Material examined.

TYPE LOCALITY. — Madagascar, off southwestern coast, 22°18’S, 43°04.7’E, 400 m.

MATERIAL EXAMINED. — Madagascar. Vauban, stn CH 50, 15°19.0’S, 46°11.8’E, 405 m, A. Crosnier coll., 8.XI.1972, 1 ovig. cl 7.8 mm, cw 8.1 mm ( MNHN-B 18272). — Stn CH 61, 23°36.1’S, 43°31.0’E, 445-455 m, A. Crosnier coll., 27.II.1973, 1 ovig. cl 8.8 mm, cw 9.1 mm ( MNHN-B 18350). — Stn CH 94, 22°18’S, 43°04.7’E, 400 m, A. Crosnier coll., 27.XI. 1973, 1 holotype ( MNHN-B 18274).

ETYMOLOGY. — From machaera (Latin for sword or dagger) in reference to the slender, straight, sword-like outer orbital teeth.

DISTRIBUTION. — Known only from Madagascar. Depth: 400-455 m ( Fig. 34 ).

SIZE. — Maximum size: cl 11.0 mm, cw 11.7 mm (MNHN-B 18274); unknown.

DESCRIPTION

Carapace of females (males unknown) broader than long ( Fig. 13A ); dorsal surface covered by small granules, short, abundant hair, particularly longer along anterior third anterolateral borders. Urogastric, cardiac regions distinct, slightly elevated; cervical, branchial grooves indistinct. Branchial regions slightly inflated along sides.

Anterior border of carapace ( Fig. 13A ) with slen- der outer orbital teeth, directed slightly outwardly but with straight tips, reaching or nearly reaching shorter frontal teeth. Frontal teeth nearly triangular, equal or nearly equal. Orbital sinuses very broad, U- or nearly V-shaped, asymmetrical (inner margins steeper than outer margins); lateral frontal sinuses U-shaped; median frontal sinus V-shaped, wider than lateral frontal sinuses, narrower than orbital sinuses.

Anterior border of endostome ( Fig. 13B ) well below posterior border of antennular fossae of basal antennular articles.

Female chelipeds (P1) (males unknown) small, slender, smooth, nearly equal; fingers 1.7 times longer than propodus, with very short teeth in holotype, small triangular teeth in two paratypes. P2 ( Fig. 13A ), P3 relatively short, thick; meri with small granules; length of P2 meri 0.8- 0.9 times cl, 4.4-5.0 times longer than broad. P4, P5 covered with short hairs; P5 dactyli slender, slightly curved.

Female abdomen (males unknown) with six somites, triangular telson; somite 3 broadest, somite 6 longest.

REMARKS

Specimens from Madagascar identified by Chen (1987) as Ethusa hirsuta McArdle, 1900 clearly do not belong to this species. In the Madagascar specimens (Chen 1987: pl. 1, fig. F) the orbital sinuses are broad and U-shaped, the outer orbital teeth are slender, the branchial regions are inflat- ed laterally, and the anterior border of the endostome lies well below the posterior border of the antennular fossae ( Fig. 13B ). Although the type material of E. hirsuta could not be examined and it is not known if it is still extant, illustrations by Alcock & McArdle (1902) and Alcock & MacGilchrist (1905) show V-shaped orbital sinuses and triangular outer orbital teeth, and the branchial region was not inflated, making the sides of the carapace look almost straight (Alcock & M c A r d l e 1 9 0 2: p l. 5 9, f i g. 2; A l c o c k & MacGilchrist 1905: pl. 72, fig. 1). The anterior border of the endostome was clearly shown to extend above the level of the antennular fossae of the basal antennular articles ( Alcock & MacGilchrist 1905: pl. 72, fig. 1a) so that “there is no distinct epistome” ( McArdle 1900: 475). It was clearly described as such (“extends forward well between the bases of the antennules”) by MacGilchrist (1905: 258). Furthermore, the description refers to the outer orbital teeth as “directed slightly outwards”. None of these characters are found among the Madagascar specimens.

Chen (1987) identified the three Madagascar specimens as E. hirsuta since they were thought to agree with McArdle’s description. Nevertheless, Chen found two differences when the specimens were compared to the figures of Alcock & MacGilchrist (1905): “an oblique indistinct ridge” on the branchial regions instead of a groove in the figure and “the lateral part of the cardiac-intestinal region being swollen” (Chen 1987: 686).

The Madagascar specimens erroneously identified as E. hirsuta were recognized by Chen (1987: 66) to have frontal and outer orbital teeth that “closely resemble those of E. indica ”. Although the shape and relative length of the frontal and outer orbital teeth of E. indica vary widely ( Chen 1985: fig. 9b), its outer orbital teeth typically are directed outwardly whereas in E. machaera n. sp. they are straighter. The meri and propodi of P2 and P3 were found to be “very long” in E. indica when compared to those of the Madagascar specimens (Chen 1987: 686). The meri of the Madagascar specimens were described as “4.5-4.8 longer than broad”. When the specimens were measured again the average ratios (N = 3) were 3.8 for P2 propodus, 3.3 for P2 carpus, 3.0 for P3 propodus, and 3.5 for P3 carpus. The average values using the same method in randomly select- ed male and female specimens (N = 7; 6,

1) of varying size of E. indica from the Philippines (MNHN-B 18926, 18164, 18159) and Indonesia (MNHN-B 22860, 22871) were 5.6 for P2 propodus, 4.5 for P2 carpus, 6.7 for P3 propodus, and 4.9 for P3 carpus. In addition to the difference in the length of P2 and P3, E. machaera n. sp. has denser hair on the dorsal surface of the carapace as well as on P4 and P5 than E. indica .

Figures

FIG. 13. — Ethusa machaera n. sp., holotype cl 11.0 mm, cw 11.7 mm, off southwestern coast of Madagascar, Vauban, stn CH 94, 400 m (MNHN-B 18274); A, dorsal surface of carapace and P2; B, ventral view of anterior portion of body. Scale bars: A, 5 mm; B, 2 mm.

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