Chelyosoma productum Stimpson, 1864
Common name(s): Flattop sea squirt, horseshoe ascidian
|Chelyosoma productum from 75 m depth, San Juan Channel. Width of upper flattened disk on which the two apertures are located is 2.5 cm. This large individual has numerous diatoms and other fouling organisms attached to the tunic.|
|(Photo by: Dave Cowles, July 2008 )|
How to Distinguish from Similar Species:Chelyosoma columbianum has disk plates without concentric growth lines, the muscle strands connecting the two central disk plates are visible (at least in preserved specimens), there are one to 3 intermediary plates between the plates surrounding the apertures and the margin of the disk, and the disk diameter rarely is greater than 1.5 cm.
Geographical Range: Prince William Sound, Alaska to San Diego, CA. Those in the southern end of the range are usually smaller.
Depth Range: Low intertidal and subtidal to 50 (75) m depth
Habitat: Rocks; common on floats and pilings. Often several individuals are clumped together. Mostly in quiet waters.
This species is known to feed on barnacle and copepod nauplii (larvae),
eggs, and the larvae of gastropods and other ascidians. It reproduces
in spring, releasing its gametes in the early morning (it does not brood
its young). Fertilized eggs, which may be tan, yellow, or purple,
hatch into tadpole larvae in 29-40 hours at 11C. After swimming for
a few hours to a few days, the larvae settle, preferring to settle on the
tunics of individuals of the same species.
Predators include the seastar Orthasterias koehleri and the gastropodFusitron oregonensis (Oregon triton), which eats mostly large individuals (over 1.4 cm diameter). Several commensal copepod species may be found inside the branchial chamber.
This species may contain up to 800 ppm of the metal vanadium in the
tunic by weight.
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Johnson and Snook, 1955
Lamb and Hanby, 2005
Morris et al., 1980
O'Clair and O'Clair, 1998
General Notes and Observations: Locations,
abundances, unusual behaviors:
In this closeup view , the two siphons can be seen opening on the tunicate's upper surface. Several of the fouling organisms are also visible, such as the entoprocts seen above the siphon on the left.