Thursday, April 26, 2012

Phyllodocid metatrochophore

Polychaete metatrochophore larvae like this one were collected in plankton tows off the docks in Charleston, OR in April.  I identified them as members of the family Phyllodocidae, largely due to the presence of their leaf-like dorsal cirri.  Cirri are fleshy projections found on polychaete segments (e.g. prostomium, peristomium or pygidium) or their parapodia (appendages bearing chaetae).  Phyllodocid polychaetes have rounded dorsal (and sometimes ventral) cirri on each parapodium.  The cirri of this metatrochophore were particularly leaf-like in their shape and texture, which is a characteristic of the genus Phyllodoce (Crumrine 2001).  This image is a lateral view (anterior up) showing the distinct dorsal cirri, one of the two red eye spots, and the prototroch (a transverse ciliated band encircling the larva at its widest point).  One can also see the four pairs of long finger-like tentacular cirri just posterior to the prototroch.  The second image was taken at a higher magnification to show the leaf-like characteristics of the dorsal cirri.

I kept one of these metatrochophores in a sea table in our lab. When I checked in on it several days after collection, I discovered that it had grown into a juvenile worm and was crawling around on the bottom of the bowl.  At first glance this juvenile looks rather different from the metatrochophore in the above photographs.  But with closer examination, one can see the foliaceous dorsal cirri and the four pairs of long tentacular cirri just posterior to the oval prostomium (anterior-most segment bearing eyes).  The characteristics of both the metatrochophore and the juvenile suggest that this specimen belongs to the genus Phyllodoce.  Identification to species requires examination of the polychaete’s proboscis (the large semi-transparent shape that can be seen through the body wall in this picture).  The arrangement of papillae on the surface of the everted proboscis is a species-specific characteristic within this genus (Carlton 2007). But unfortunately this worm did not evert its proboscis while I was watching, and so the species remains undetermined.   

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. 

No comments:

Post a Comment