Peanut Worms (Sipunculids and Echiurans)

The now obsolete taxon of Vermes once encompassed all non-arthropod invertebrates.  This wall chart compares two different phyla of worm; sipunculids and echiurans.  Both groups have previously been classified with in the Annelida despite their lacking the segmentation and bristled parapodia characteristic of this group. They are now both classified as seperate phyla within a group known as the Lophotrochozoa based on both larval development (14 & 15) and ribosomal DNA evidence.  A typical sipunculid (peanut worm) has an introvertible anterior region often with a crest of tentacles (1, 2, & 3). Different species burrow into sediments, rocks or calcified organic structures with the anterior end protruding. Echiurans are found in soft sediments with a long proboscis extending to the surface of the sediment where organic particles settle down onto a ciliated gutter which moves food to the mouth via the proboscis (10).