The Terrible Ellid Worm – Thelepus crispus

Well, really, it's not terrible at all - in fact it's a rather interesting 15 cm-long worm that hides under rocks in the intertidal zone along Pacific Northwest rocky shorelines. This worm belongs to the Family Terribellidae, one of several dozen families of worms in the Class Polychaeta of the phylum Annelida.

These segmented worms usually have multiple bristle-like apendages, a pair for each segment, thus the name "poly" (many) and chaete (bristles). Terribelid worms are characterized by the long, flexible thin tentacles that reach out from the end of a tube the animal builds from mud, shells or sand under a rock. Each of the white tentacles has a ciliated groove that carries particles of food to the mouth. The system is like a large array of conveyor blelts feeding food to the mouth of the worm, while it sits comfortably hidden in its tube beneath the rock. The short bright red tentacles are gills, filled with red blood cells containing a type of haemoglobin similar to our own. This molecule (or class of molecules) is a good "grabber" of oxygen, allowing the worm to live in oxygen-poor environments. Another name for this worm is "the hairy-gilled" worm, but the real "hairy" part is the feeding system, not the gills.