The Sipuncula or Sipunculida is a class containing about 162 species of unsegmented marine annelid worms. Sipuncula was once considered a phylum, but was demoted to a class of Annelida, based on recent molecular work.
Sipuncula
Sipunculus nudus
Lecthaylus gregarius, a sipunculan from the Silurian of Illinois.
A plate of Sipunculid worm jelly.
The annelids, also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.
Annelid
This sabellid tubeworm is budding
Burgessochaeta setigera
Phylogenetic tree of early lophophorates