Chelysoma columbianum Huntsman, 1912

Common name(s): 

Phylum Chordata
Subphylum Urochordata
Order Phlebobranchia
Family Corellidae
Chelyosoma columbianum collected at 120 m depth west of Yellow Island, San Juan Channel, WA.  The scale below is millimeters
(Photo by: Dave Cowles July 2007)
Description:  This solitary ascidian is translucent and attaches via a wide base to the substrate.  Both the oral and atrial siphons are on a flattened disk made up of several plates (see photo above).  There is a raised rim around the disk (photo).  The disk plates do not have concentric growth lines.  The muscle strands connecting the two central disk plates (and those connecting other plates as well) are visible through the tunic (photo).  Disk diameter up to 1.5 cm.

How to Distinguish from Similar Species:  Chelyosoma productum looks very similar but its disk plates have concentric growth lines and the muscle strands connecting the two central plates are not visible (at least when preserved).  It also can grow to greater than 1.5 cm disk diameter and can occasionally be found intertidally.

Geographical Range:

Depth Range:  Subtidal


Biology/Natural History:



Dichotomous Keys:
  Kozloff 1987, 1996

General References:

Scientific Articles:

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

This closeup of the disk shows both the oral and the atrial apertures and a few of the outlines of the plates the disk is made of.  The white muscle fibers which bind the plates together are visible in the tissue behind the disk.
The two white, calcified-appearing lumps at the left end of the disk appear to be part of the animal but I don't know what they are.

This side view of one of the siphons shows the raised rim of the plate and the fact that the aperture is ringed with small protuberances.  These are probably used to close the aperture.

Authors and Editors of Page:
Dave Cowles (2007):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)