Nephtys sp. metatrochophore

This is a metatrochophore larva of a nephtyid polychaete (family Nephtyidae).  In April and May 2012, we frequently encountered these larvae in plankton samples from Coos Bay, OR.  These larvae are propelled by two ciliary bands - an anterior prototroch and a posterior telotroch. The prominent red pigment bands near the prototroch and pygidium (the posterior-most segment) inspired me to look at them more closely.  Upon closer inspection, one can see striking blue (!) pigment in the lining of the gut.  Also in the gut, is this larva’s most recent meal, a centric diatom.  We determined that this larva belongs to the genus Nephtys due to the distinct red and blue pigments mentioned above as well as the dome shaped episphere and a single pair of red eyes (Crumrine 2001).  

In one week, this planktonic larva turned into a benthic juvenile polychaete (left) displaying additional characteristics of Nephtys species.  These predatory worms commonly found burrowing in mudflats use an eversible pharynx armed with a pair of jaws (visible in the third picture as two glowing arrowheads) to capture and subdue prey such as mollusks, crustaceans or other polychaetes.  Furthermore, we noticed that the juvenile possessed an anal cirrus (looks like a small sphere on the pygidium in the bottom photograph).  The presence of an unpaired anal cirrus is  characteristic of Nephtys species, although it is often lost when adults are handled.  

There are more than six species within this genus in the NE Pacific, but N. caeca and N. caecoides are most common (Rudy and Rudy 1983).  To identify species within this genus, one must examine the interramal cirri (slender projections between parapodial branches) on the adult parapodia (Carlton 2007), which was not possible for this juvenile stage.    

Crumrine, L.  2001.  Polychaeta. In: An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest.  Edited by Alan Shanks.  OSU Press, Corvallis.

Carlton, J T.  2007.  The Light and Smith Manual:  Intertidal Invertebrates from Central California to Oregon 4th Edition.  University of California Press, Berkeley. 

Rudy, P and L Rudy.  1983.  Oregon Estuarine Invertebrates: An Illustrated Guide to the Common and Important Invertebrate Animals.  Oregon Institute of Marine Biology, Charleston, OR.