The Collaborative International Dictionary
Rissoid
Rissoid \Ris"soid\, n. [NL. Rissoa, the typical genus ( fr. A. Risso, an Italian naturalist) + -oid.] (Zo["o]l.) Any one of very numerous species of small spiral gastropods of the genus Rissoa, or family Rissoid[ae], found both in fresh and salt water.
Wiktionary
rissoid
n. (context zoology English) Any of the spiral gastropods of the genus (taxlink Rissoa genus) or family ''(taxlink Rissoidae family)'', found both in fresh and salt water.