Pacific Tube Anemone, Pachycerianthus fimbriatus

Pacific Tube Anemone, Pachycerianthus fimbriatus. Underwater photograph taken in coastal waters off La Jolla, California, August 2019. Photograph courtesy of Bob Hillis, Ivins, Utah.

Pacific Tube Anemone, Pachycerianthus fimbriatus. Underwater photographs taken in the coastal waters off Monterey, California, February 2022. Photographs and identifications courtesy of Bob Hillis, Ivins, Utah.

Pacific Tube Anemone, Pachycerianthus fimbriatus. Underwater photograph taken in the coastal waters off Isle Coronado, Baja California Sur, May 2023. Photograph and identification courtesy of Dr. Tom Bartol, Carlsbad, California.

Phylogeny:  The Pacific Tube Anemone,  Pachycerianthus fimbriatus (McMurrich, 1910), is a member of the Cerianthidae family of Tube Anemones. The genus Pachycerianthus is one of eighteen genera in this family, and there are eighteen species in this genus. They are also known as the Tube-dwelling Anamone and in Mexico as Anémona Tubo del Pacifico.

Morphology:  Pacific Tube Anemones have radial symmetry, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. Like other anemones, they have a flower-like appearance. Pacific Tube Anemones live in a parchment-like tube that is imbedded in sediment. They have a whorl of elegant, long, tentacles around their margin that extend outward and are primarily for food gathering and defense. They also have a whorl of short, erect tentacles around their mouth that are used for food manipulation. The tentacles may extend with the current, or be tightly coiled. The tube is elongate and it is made of a collagenous network of mucous and threads (ptychocysts) and therefore remains flexible. The tube is often covered by sand grains, shell fragments, and other debris. The entire animal can quickly withdraw into the tube if disturbed. Pacific Tube anemones lack the pedal disk that Sea Anemones use to anchor themselves to hard substrate and have to be buried or wedged sufficiently to hold themselves in place. Their oral disk, tentacles and stalk are smooth. They vary in color from white, orange, bluish, pink, purple, brown, or black. Sometimes, the tentacles are bi-colored. They reach a maximum of of 35 cm (13.8 inches) in height and have a crown diameter of 30 cm (11.8 inches). Their tubes can reach 2.0 m (6 feet 6 inches) in length.

Habitat and Distribution:  Pacific Tube Anemones are found mostly buried in sand, mud, or rubble substrates. They live from the lower intertidal zone to depths of 46 m (151 feet). They are primarily a temperate Eastern Pacific species.  In Mexican waters, they are found along the west coast of the Baja Peninsula, from the northern border to Isla San Martin (San Quintin area), Baja California. They are also found throughout the Gulf of California.

Diet:  Pacific Tube Anemones use their tentacles to capture small crustaceans, suspended detritus and plankton.

Predators:  Pacific Tube Anemones are preyed upon by crustaceans, fish, and the Giant Nudibranch, Dendronotus iris. The Giant Nudibranch feeds on this species by attacking the tentacles. When the Tube Anemone withdraws into its tube it sometimes brings the nudibranch with it. The nudibranch will continue feeding, but seldom kills the anemone. The tentacles  have the ability to regenerate.

Reproduction:  Pacific Tube Anemones are simultaneous hermaphrodites (having both male and female reproductive organs). They reproduce sexually, through broadcast spawning. This happens when mature gametes are shed into the coelenteron and spawned through the mouth. The fertilized egg develops into a planula larva, which then settles to the bottom substrate and metamorphoses into its adult stage.

Ecosystem Interactions:  There are no documented examples of Pacific Tube Anemones engaging in commensal, parasitic, or symbiotic relationships.

Human Interactions:   Pacific Tube Anemones have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a wide distribution and should be consider to be a species of Least Concern.

Synonyms:  Cerianthus elongatus and Pachycerianthus plicatus.