Arbacia Gray, 1835

Courville, Erwan, Poulin, Elie, Saucede, Thomas, Mooi, Rich, Lessios, Harilaos, Salinas, Andrea Martínez & Diaz, Angie, 2023, Taxonomic reassessment of Tetrapygus niger (Arbacioida, Echinoidea): molecular and morphological evidence support its placement in Arbacia, Zootaxa 5375 (2), pp. 249-261 : 254

Genus Arbacia Gray, 1835

Type species. Arbacia lixula ( Linné, 1758) . Extant species with a wide distribution across the Atlantic Ocean, including the Brazilian coast, the Gulf of Guinea, the Azores, the East Atlantic Islands, and the Mediterranean Sea. The genus is also known from the Pleistocene of Madeira, Azores, and Italy ( Madeira et al. 2011; Stefanini 1911).

Emended diagnosis. Arbaciidae with ocular plates bearing small tubercle, usually resorbed during ontogeny; periproct slightly elongated in direction 1-IV and covered with four supra-anal plates; ocular pores double, not visible externally; peristome large (> 30% TD), the ambulacra protruding so as to form “ambulacral lips”; buccal notches shallow and wide; tags narrow, more or less elongated; oral primary spines with a cortex-layer “shoe” or “cap”; the ambital and upper spines without any cortex-layer; sphaeridia single, in a small pit close to the peristomial edge; epistroma conspicuously developed and may be of a characteristic design, forming randomly distributed punctation, or arranged in horizontal or vertical series.