Shellfish and Univalve

Shellfish noun - Invertebrate having a soft unsegmented body usually enclosed in a shell.

Univalve and shellfish are semantically related. In some cases you can replace term "Univalve" with "Shellfish", this nouns are similar.

Univalve noun - A class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes.

Shellfish and univalve are semantically related. You can use "Shellfish" instead a noun "Univalve".