Galeomma Turton, 1825

Oliver, P. Graham & Holmes, Anna, 2004, Cryptic bivalves with descriptions of new species from the Rodrigues lagoon, Journal of Natural History 38 (23), pp. 3175-3227 : 3197

Genus Galeomma Turton, 1825

Type species: Galeomma turtoni Sowerby, 1825 .

Galeomma sagenata n. sp.

( figures 75–77 )

HOLOTYPE: one specimen, live collected, Passe Demi , Rodrigues, 15 m, 19 ‡ 42.104 ’ S, 63 ‡ 17.570 ’ E. NMW. Z.2001.061.00023.

Description. Shell 4.81 6 2.22 mm. Thin, hyaline, valves gaping to almost 180 ‡, mantle covering valves and non-retractable. Subequilateral, beaks just in front of midline. Outline oblong; dorsal margin long, straight; anterior margin rounded, posterior margin slightly angulate; ventral margin long, more or less straight with a slight median sinus. Sculpture ( figure 76 ) reticulate, fine cords demarcating diamond-shaped areas, intersections of cords extended into low spines; margins deeply denticulate. Prodissoconch ( figure 77 ) large, with weak concentric lines, PdI 340 M m in diameter. Hinge teeth obsolete, internal resilium small; external ligament extending either side of beaks, about half the length of the dorsal margin.

Mantle white in colour, decorated by sparse globular tubercles. Exhalant and inhalant/pedal apertures small, the latter in the form of a short funnel.

Derivation of name. From the Latin sagena ‘a fish net’, referring to the coarse netted sculpture.

Habitat. Collected from a sample of coral rubble from 18 m off the reef front.

Remarks. The sculpture of this species is highly distinctive and we could find no described species with any similarity. The majority of the species described by Deshayes (1856a) have a weak radial sculpture and others are simply granular. The very distinctive nature of this shell gives us confidence to erect a new species based on a single example.

Figures

FIGS. 75–80. (75–77) Galeomma sagenata holotype, NMW.Z.2001.061.00023, external (SEM). (78–80) Galeomma sp., NMW.Z.2001.061.00024, external (SEM).