Pachycerianthus fimbriatus McMurrich 1910

This anemone-like species lives in a slippery black tube that they secrete. It has two rings of slender, translucent brownish, purplish-black, orange, or light colored tentacles. The inner ring may be held over the mouth while the outer ring is extended further. Animal length to 35 cm. Tube up to about 2.5 cm diameter and may be more than a meter long.

How to Distinguish from Similar Species: This is the only member of this Subclass in our area. Other members of the subclass include black corals

Biology/Natural History: This anemone-like cerianthid lives in a soft, black, slimy tube that may extend a meter or farther into the sediment. The tube extends slightly above the sediment and is made of a secretion of nematocyst-like organelles called ptychocysts. The cerianthid quickly withdraws into the tube when disturbed, and may leave a star-shaped track in the mud around the tube entrance with its tentacles when it withdraws. Predators include the nudibranch Dendronotus iris, which may be drawn into the tube and continue feeding when the cerianthid withdraws. Dendronotus iris attaches its eggs to the tube of the cerianthid, which appears to be its principal prey. Feeding by the nudibranch usually does not kill the cerianthid. The aboral end of the cerianthid is pointed and adapted to digging. Cerianthids differ from anemones in several ways, such as having an aboral anal pore. Cerianthids have unusually rapidly-conducting nervous systems for Anthozoans. Some cerianthids have fluorescent tentacles.

Very soft mud such as bays and harbors. Sometimes in sand.

Geographical Range: Southern Alaska to Isla San Martin, Baja California

Depth Range: Rarely intertidal, mostly subtidal to at least 54 m

Pachycerianthus fimbriatus is a cerianthid anemone that burrows in substrate and lives in a semi-rigid tube made of felted nematocysts. The anemone is often seen in bright orange to red.

Like most anemones, the tube-dwelling anemone contains stinging cells or nematocytes along its tentacles, however, the cells are not toxic to humans.

The ceriantharia possess two whorls of tentacles, one surrounding the mouth (labial tentacles) and one at the edge of the oral disc (marginal tentacles).