Unidentified polychaete metatrochophore

This is a metatrochophore larva of an unidentified polychaete annelid that I collected from a January 2012 plankton tow off the docks in Charleston. Its gut contains a large number of yolk droplets (of various color and size). Yolk droplets of this kind are often found in eggs of annelids with lecithotrophic larvae (meaning they do not feed and derive nutrition from maternal supplies), e.g. in larvae from the family Nereidae.  This suggests that this is likely a lecithotrophic larva.  One can also see two ciliary bands. The broad ciliary band just posterior to the ocelli (eyes) is called the prototroch. The narrow band near the posterior end is called the telotroch. These are used for locomotion. In planktotrophic (feeding) larvae the prototroch may also be used for collecting food particles. This larva has three setigers (segments that bear setae), which is how we know it is an annelid.