earthworm vs oligochaete

earthworm and oligochaete both are nouns.

Word	Noun	Adjective	Verb	Adverb
earthworm	Yes	No	No	No
oligochaete	Yes	No	No	No

As nouns, oligochaete is a hypernym of earthworm; that is, oligochaete is a word with a broader meaning than earthworm:

earthworm: terrestrial worm that burrows into and helps aerate soil; often surfaces when the ground is cool or wet; used as bait by anglers
oligochaete: hermaphroditic terrestrial and aquatic annelids having bristles borne singly along the length of the body

Other hypernyms of earthworm include oligochaete worm.

earthworm (noun)	oligochaete (noun)
terrestrial worm that burrows into and helps aerate soil; often surfaces when the ground is cool or wet; used as bait by anglers	hermaphroditic terrestrial and aquatic annelids having bristles borne singly along the length of the body