The Echinoid Directory

Contributed by Heinke Schultz, August 2007

Arbaciella Mortensen, 1910, p. 327

Diagnostic Features	Small (the type is 7 mm in diameter); test low hemispherical, oral side flattened, ambitus sharp. Apical disc dicyclic; ocular and genital plates with radiating ridges; periproct with four large anal plates. Ambulacra trigeminate, slightly widened phyllodes; primary tubercles only on oral side and at the ambitus; on upper side distinct glassy pegs. Interambulacra: on oral side and at the ambitus up to two large tubercles per plate, of same size as ambulacral primary tubercles; the plates of the aboral side are set with more or less horizontal series of glassy pegs, the largest connected vertically to its neighbours by a narrow, vertical epistromal ridge. Peristome very large (about 60% of test diameter), naked except of five pairs of oval buccal plates, small platelets embedded in the membrane. Shallow buccal notches present. Spines longest around the ambitus (about 2 mm), shape leaf-like with a pointed tip, in cross-section triangular; on upper side median keel, each side slightly excavated, underside of spines with longitudinal ridges below a distinct cap. Single perradial sphaeridial pit.
Distribution	Recent, West Africa, Mediterranean. ?Danian Europe, Kazachstan
Name gender	feminine
Type	Arbaciella elegans Mortensen, 1910 p. 328, by original designation.
Species Included	A. elegans Mortenen, 1910; Recent, West Africa and the Mediterranean A. regularis (Arnaud, in Cotteau, 1887); Danian, France
Classification and/or Status	Euechinoidea, Echinacea, Arbacioida, Arbaciidae Monotypic.
Remarks	Mortensen (1910) stated, that this species looks very similar to young specimens of Arbacia lixula. But it differs by the total lack of aboral spines. He considered that Arbaciella might be a paedomorph of Arbacia. Last doupts on the validity of the genus were eliminated by the work on the microstructure of Arbaciella by Regis (1982). Arbaciella elegans was reported to live in the Mediterranean on the valves of Pinna, a bivalve, (Giacobbe & Rinelli, 1992). Recently it was found in the crevices of Lithotamnion, an incrusting Red Algae (Baumeister & Koch 1998). This species bears a striking resemblance to Podocidaris ornata (H.L. Clark 1912). It remains to be seen how these two taxa differ. Mortensen, T. 1910. Arbaciella elegans. Eine neue Echiniden-Gattung aus der Familie Arbaciidae. Mitteilungen des Naturhistorischen Museum Hamburg, 27: 327-334. Regis, M.B. 1982. Donnes microstructurales et validite du genre Arbaciella Mrtsn (Echinodermata-Echinoidea). Memoires sur le Biologie Marine et Oceanographique 12: 5-26. Giacobbe, S. & Rinelli, P. 1992. Ecological notes on Arbaciella elegans Mortensen from populations of Pinna in the Strait of Messina. In: Scalera-Liaci, L & Canicatti, C. (eds) Echinoderm Research 1991: 185-189; Rotterdam, Balkema. Baumeister, J.G. & I. Koch 1998. Arbaciella elegans (Echinoidea: Arbaciidae) aus dem Thyrrenischen Meer. Stuttgarter Beitrage zur Naturkunde. Serie A (Biologie) 568: 1-6. Stuttgart