Description: Members of Family Spirorbidae have most or all segments not longer than wide. The head has a series of radioles and an operculum. Members of the family are quite small and build a distinctive coiled, calcareous tube attached to the substrate (the part that attaches to the substrate is the dorsal side). The thoracic region of the worm's body has only 4 setigers. Circeis spirillum builds a thin, translucent calcareous tube that is round in cross section and always spirals dextrally (counterclockwise). The end of the tube usually points upward from the substrate (but not in this individual). The collar setae are obliquely geniculate, and have cross striations. The embryos are attached singly to the inside of the tube.
How to Distinguish from Similar Species:Circeis armoricana has collar setae that are sharply geniculate and have no cross striations, the tube is porcellanous rather than clear, and it lives on shells, kelp, or decapods. Several Spirorbis species have tubes that coil sinestrally (clockwise).
Geographical Range: Circumboreal (Arctic, North Pacific, and North Atlantic), but no farther south than where the water reaches 15 degrees C in August.
Depth Range: Subtidal
Habitat: Grows attached to bryozoans and hydroids
Kozloff, 1987, 1996
General Notes and Observations: Locations, abundances, unusual behaviors:
Authors and Editors of
Salish Sea Invertebrates web site provided courtesy of Walla