Also found in: Thesaurus, Medical.
Any of various amoeboid protozoans having a hard external covering, found in soil and freshwater habitats.
[From New Latin Testācea, former order name, from Latin, neuter pl. of testāceus, covered with a shell, from testa, shell.]
(Animals) any of various invertebrate animals with a hard shell
(Zoology) (of an invertebrate) having a hard shell