Actinozoan and Cnidarian

Actinozoan noun - Sessile marine coelenterates including solitary and colonial polyps; the medusoid phase is entirely suppressed.

Cnidarian and actinozoan are semantically related. In some cases you can use "Cnidarian" instead a noun "Actinozoan".

Cnidarian noun - Radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures; they occur in polyp and medusa forms.

Actinozoan and cnidarian are semantically related. Sometimes you can replace term "Actinozoan" with "Cnidarian", this nouns are similar.