Mollusca vs phylum

Mollusca and phylum both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mollusca	Yes	No	No	No
phylum	Yes	No	No	No

As nouns, phylum is a hypernym of Mollusca; that is, phylum is a word with a broader meaning than Mollusca:

Mollusca: gastropods; bivalves; cephalopods; chitons
phylum: (biology) the major taxonomic group of animals and plants; contains classes

Mollusca (noun)	phylum (noun)
gastropods; bivalves; cephalopods; chitons	(biology) the major taxonomic group of animals and plants; contains classes
	(linguistics) a large group of languages that are historically related