Edoneus Holthuis, 1978

Cai, Yixiong & Husana, Daniel Edison M., 2009, Cave Shrimps Of The Genus Edoneus Holthuis, 1978, From Luzon, The Philippines, With Descriptions Of Three New Species (Crustacea: Decapoda: Atyidae), Raffles Bulletin of Zoology 57 (1), pp. 51-63 : 52

Edoneus Holthuis, 1978

Edoneus Holthuis, 1978: 219 ; 1993: 51.

Type species: Edoneus atheatus Holthuis, 1978 , by monotypy; gender: masculine.

Diagnosis. – Body moderately robust, eyes developed or reduced; rostrum short; pterygostomian margin broadly rounded; supraorbital spine absent; ventral margin of pleura rounded; telson with a very tiny posteromedian projection; distal margin with intermediate pairs of setae much shorter than lateral pair of spines; palp of first maxilliped ending in finger-like projection, flagellum of the exopod very short, endopod high, as long as or distinctly exceed the flagellum of exopod in length; pereiopods without exopods; first and second pereiopods with chelae monomorphic, palm well developed, fingers tipped with brushes of long setae, carpus of first pereiopod moderately excavated anteriorly, twice longer than broad; carpus of second pereiopod much slender than previous one, not excavated anteriorly; branchial formula incomplete, with 6 or 7 pairs of gills, no arthrobranch on pereiopods; no arthrobranch, or with only one very small arthrobranch on base of third maxilliped; podobranch of second maxilliped less developed or vestigial; epipods present on first 4 pereiopods; first pleopod of male with endopod sub-rectangular, no appendix interna at endopod; second pleopod of male with appendix masculina rod-shaped, slender, spinose on inner surface; Uropodal diaeresis bearing 14–24 movable spinules, with outermost one distinctly longer than lateral angle. Ovigerous females with large eggs, sized 0.90–1.10 × 0.55–0.60 mm.

Distribution. – Known only from several caves in Atimonan, Quezon province and the northern part of Luzon, the Philippines.

Habitat. – All four species reported here were found in the subterranean water in caves of Luzon Island, northern Philippines.

Remarks. – Three undescribed species of atyids from a recent collection from caves in Luzon, the Philippines, share numerous characters with Edoneus atheatus Holthuis, 1978 , except for the presence of one arthrobranch on the third maxilliped in the former three. This difference is attributed to interspecific variation. Interspecific variation of the number and size of arthrobranchs in the third maxilliped have also been found in the genus Parisia ( Holthuis, 1956a, b). We redefine the genus Edoneus here to include the newly discovered species. In the original description, Holthuis (1978) described the branchial formula as follows: “In all, five pleurobranchs are present at the bases of the pereiopods; no other pleurobranch were observed, neither were any arthrobranchs or podobranchs.” His figures ( Holthuis, 1978: Figs. 5-i ), however, showed a lamina-shaped vestigial podobranch at the base of second maxilliped. Holthuis (1978: 220) also described the telson of E. atheatus as follows: “short hairs are implanted on the posterior margin of the telson above the spines; the margin itself shows no median tooth.” The examination of topotypical specimens of E. atheatus from the type locality in the present study shows that there is a very tiny posteromedian projection on the posterior margin of the telson (see Fig. 1A ). This structure agrees with that of the new species described herein, and is regarded as diagnositic character for the genus. Edoneus thus includes four species, all of which are endemic to Luzon, the Philippines.

Edoneus is most similar to Parisia Holthuis, 1956 , from Madagascar, Australia ( Williams, 1964), and Luzon (Cai & Anker, 2004). It can only be differentiated from Parisia by the presence of a very small posteromedian projection on the telson (vs. posteromedian projection on telson absent), the lateral angle of the uropodal diaeresis being distinctly shorter than the outermost spinules (vs. lateral angle of uropodal diaeresis much longer than outermost spinules), and minor differences in the branchial formula, viz., no or one arthrobranch on the base of third maxilliped (vs. one or two arthrobranchs). With respect to the short lateral angle of uropodal diaeresis, and the absence of one arthrobranch on the first pereiopod, Edoneus resembles to Lancaris , a genus that was recently described from highlands of Sri Lanka (Cai & Bahir, 2005). It, however, differs by the absence of an appendix interna on the male first pleopod, which is present on species of Lancaris ; and the posterior setae on the telson, in which, the median pairs of setae are much shorter than the lateral pair (vs. much longer in species of Lancaris ).

Figures

Fig. 5. Edoneus sketi, new species: A, first pereiopod; B, second pereiopod; C, third pereiopod; D, dactylus of third pereiopod; E, fifth pereiopod; F, dactylus of fifth pereiopod; G, male first pleopod; H, male second pleopod; I, uropodal diaeresis. Scale bars: A–C, E = 0.5 mm; D, F, I = 0.1 mm; G, H = 0.2 mm; (male, cl 4.1 mm, paratype, ZRC).

Fig. 1. Edoneus atheatus. A, telson; B, second maxilliped; C, fist pereiopod; D, second pereiopod; E, uropodal diaeresis. Scale bars: A, E = 0.1 mm; B–D = 0.3 mm. (male, cl 2.9 mm, RMNH).