red-bellied turtle vs red-bellied terrapin

red-bellied turtle and red-bellied terrapin both are nouns.

Word	Noun	Adjective	Verb	Adverb
red-bellied turtle	Yes	No	No	No
red-bellied terrapin	Yes	No	No	No

As nouns, red-bellied turtle and red-bellied terrapin are synonyms defined as:

red-bellied turtle and red-bellied terrapin: freshwater turtle of Chesapeake Bay tributaries having red markings on the lower shell

Other synonyms of red-bellied turtle include Pseudemys rubriventris, redbelly.

red-bellied turtle (noun)	red-bellied terrapin (noun)
freshwater turtle of Chesapeake Bay tributaries having red markings on the lower shell	freshwater turtle of Chesapeake Bay tributaries having red markings on the lower shell