The Collaborative International Dictionary of English v.0.48:

Nerita \Ne*ri"ta\, prop. n. [L., a sort of sea mussel, Gr.
   nhri`ths, nhrei`ths.] (Zool.)
   A genus of marine gastropods, mostly natives of warm
   climates.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nerita
    n 1: a neritid gastropod having a short smooth or spirally
         ridged shell with thick usually toothed outer lip and
         toothed operculum