nauplius
Concise Oxford English Dictionary © 2008 Oxford University Press:
nauplius /ˈnɔːplɪəs/
▶noun (pl. nauplii /-plɪʌɪ, -plɪiː/) Zoology the first larval stage of many crustaceans, having an unsegmented body and a single eye.
– origin C19: from L., denoting a kind of shellfish, or from the Gk name Nauplios, the son of the sea god Poseidon in Greek mythology.
'nauplius' also found in these Oxford entries:

