Costasiella nonatoi Ev. Marcus and Er. Marcus, 1960
"Body whitish, with much melanic pigmentation. Cerata black, except tips, with greenish knobby diverticula visible in some specimens; scattered white areas toward tips of cerata. A distinctive whitish mask surrounds the large black eyes. Rhinophores short, with white tips, fused to each other anteriorly and to the snout at their anterior base; snout of head forming two broadly rounded lobes. Cerata clavate, arranged in 3-4 densely packed rows on each side. Foot not transversely divided; tail long and narrow. Length, to 5 mm." (Marcus, 1984, The Nautilus 98(2), p. 93).
Ground color is predominately black with a white stripe along the anterior edge of the foot, and a white line up the outer edge of each rhinophores to the white tip. The cerata are white-tipped and there is a large white patch around each eye.
Length reaches 5 mm.
Found on an eating the alga, Avrainvillea nigricans. Individuals burrow into the thallus of this alga to feed and oviposit (Marcus, 1984). This species also often occurs with Costaseilla ocellifera (Marcus, 1984).
The type locality of this species is northeast of Santos, Brazil. Its range includes Brazil and the Caribbean.
Guiry, M.D. & Guiry, G.M. 2011. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 18 January 2011.