sea spider vs pycnogonid

sea spider and pycnogonid both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea spider	Yes	No	No	No
pycnogonid	Yes	No	No	No

As nouns, sea spider and pycnogonid are synonyms defined as:

sea spider and pycnogonid: any of various small spiderlike marine arthropods having small thin bodies and long slender legs

sea spider (noun)	pycnogonid (noun)
any of various small spiderlike marine arthropods having small thin bodies and long slender legs	any of various small spiderlike marine arthropods having small thin bodies and long slender legs