'Rissoid' definitions:

Definition of 'Rissoid'

From: GCIDE

Rissoid \Ris"soid\, n. [NL. Rissoa, the typical genus ( fr. A. Risso, an Italian naturalist) + -oid.] (Zool.) Any one of very numerous species of small spiral gastropods of the genus Rissoa, or family Rissoidae, found both in fresh and salt water. [1913 Webster]