Crisia occidentalis Trask, 1857
|Crisia occidentalis, about 3 cm tall.|
|(Photo by: Dave Cowles, August 2006)|
How to Distinguish from Similar Species: Of the bryozoans with erect branching colony and a biserial row of zooecia, Crisia pugeti and Crisia serrulata have an ooeciostome that is curved or bent forward. Crisia maxima has straight ooeciostomes the branches, rather than bending toward one another or ending with spikelike projections at their tips, are straight with long internodes. This species closely resembles Crisia eburnea from the Atlantic.
Geographical Range: Abundant in San Francisco Bay. Found at least from Los Angeles to Puget Sound. Reported from Jamaica (but see note above on C. eburnea)
Biology/Natural History: Cyclostome bryozoans are mostly marine, have tubular, calcareous zooecia, and the aperture is usually circular. They have no operculum. Embryos develop in ovicells which are seen as swellings on the colony. The current created by the cilia in this species is surprisingly strong. I watched particles from a distance of 4-5x the length of the lophophore tentacles become entrained in the current, drawn toward the tentacles, and blown away again, all within about 1/2 second. This species does not have a long planktonic stage.
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Johnson and Snook, 1955
Parker, T. and V. Tunnicliffe, 1994. Dispersal Strategies of the Biota on an Oceanic Seamount: Implications for Ecology and Biogeography Biological Bulletin 187: 3 336-345. (Found Crisia occidentalis on Cobb Seamount, 510 km offshore of the Oregon coast. The species does not have a long pelagic stage.
In this view one can see the double (biserial) row of zooecia along the branches, the round apertures without opercula, and the slight curving of the tips of the branches inward.
An Ooeciostome, or opening for the reproductive ovicell, can be seen in the center of the central branch near the lower third of the picture. Note that it is a straight, slitlike opening.
Several joints can also be seen in the branches, which gives the colony more flexibility.
This closeup of a branch tip shows several zooids with extended lophophores. Cilia (visible as fuzzy edges to the lophophore tentacles) beat rapidly on the lophophores, creating a strong water current which flows into the center of the lophophore cup and out between the tentacles.