Gastropod and Shellfish

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

Shellfish and gastropod are semantically related. In some cases you can use "Shellfish" instead a noun "Gastropod".

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

Gastropod and shellfish are semantically related. Sometimes you can replace term "Gastropod" with "Shellfish", this nouns are similar.