Yellow-bellied Ribbon Worm        Paranemertes peregrina

This interesting six inch worm is a member of a major group of animals called Nemertea or ribbon worms.  Yellow-bellied Ribbon Worms occur from the Bering Sea to southern California and are very common burrowing in the low intertidal zone on sandy mud beaches.

Nemertea represent an advance in worm design over their distant cousin the flatworm by sporting an anal opening. However their lack of body segments make them simpler than polychaete worms.  In addition they possess a unique weapon, a proboscis, that is shot out capturing prey by either wrapping around the victim or piercing the body with a stylet and injecting poison.  The proboscis is then withdrawn and the victim (usually a polychaete worm) is swallowed whole. Interestingly Ribbon worms lack long-range sensors so they have to bump into their prey to detect them.

Nemertea are also unique in being very long for the width of the body - some reaching up to 75 feet and many species will fragment into tiny pieces when handled.  Fortunately these fragments will grow into a complete animal.

They breed in the late spring by releasing eggs and sperm.  While most species of Nemertea develop directly into an adult, some species have a fascinating larval form called a pilidium (resembling a Roman helmet).  After swimming for a while, a cavity forms separating the intestine of the larvae from the rest of the body. The intestine then develops into an adult form within the larva, breaking free to begin its life.