Definition of Nemertea
: a class or other category of Platyhelminthes comprising soft-bodied often brightly colored unsegmented acoelomate worms that have an anterior mouth and posterior anus, a long eversible proboscis, and a definite circulatory system, are typically elongate and contractile, and are usually marine and littoral and burrow in sand or mud though a few live in fresh water or on land — see anopla , enopla
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