Definition of Sipunculoidea
1
: a group of marine worms of obscure systematic position that are commonly classed as a division of Gephyrea and that lack setae and have the mouth at the end of a retractile introvert similar to a proboscis and usually provided with tentacles and the anus anterior and dorsal
2
in some classifications
a
: a group coextensive with Gephyrea
b
: a class or other group comprising Sipunculoidea (see sense 1 above) and Priapuloidea
