Sweet Potato Sea Cucumber, Caudina arenicola

Sweet Potato Sea Cucumber, Caudina arenicola. Collected from a tidal pool of Bahía Santa Rosalillita, Baja California, August 2019. Collection, photograph and identification courtesy of Barry Mastro, Escondido, California.

Sweet Potato Sea Cucumber, Caudina arenicola. Collected off the “beach” in Agua Verde, Baja California Sur, March 2020. Collection, photograph and identification courtesy of Barry Mastro, Escondido, California.

Phylogeny: The Sweet Potato Sea Cucumber, Caudina arenicola (Stimpson, 1857) is a member of the Caudinidae Family of Sea Cucumbers. The genus Caudina is one of five genera in this family, and there are six species in this genus. This species is also known as the Sea Sweet Potato. In Mexico it is called papa dulce.

Morphology: The Sweet Potato Sea Cucumber has a thick fusiform body with smooth leathery skin. They are mottled orange in color. They have fifteen very small tentacles that contract into circular groove at the margin of the mouth where they are concealed.  Each tentacle has a short peduncle with 4 or 5 finger-like projections at the disk-like summit.  The oral ring is composed of 5 slender projecting pieces that are branched below and notched above. They do not have tube feet or elongated tentacles. Sweet Potato Sea Cucumbers reach a maximum of 25 cm (10 inches) in length.

Habitat and Distribution: The Sweet Potato Sea Cucumber resides partially buried in mud or sand, and may burrow under the sand to depths up to 40 cm (16 inches) but normally resides near the surface. They are found along subtidal coastal habitats and to depths of at least 60 m (197 feet).   In Mexican waters the Sweet Potato Sea Cucumber is only known to be found between Estero de Punta Banda, Ensenada and the USA border along the extreme northwest coast of Baja. The first collection photographed above represents a 650 km southerly range extension to the central west coast of Baja. The second photograph strongly suggest its presence in the Sea of Cortez.

Diet:  Sweet Potato Sea Cucumbers feed by ingesting sand on a continuous basis and then removing and consuming the associated microbes and detritus. The retain a large amount of sand within their body at all times affording them with an inflated appearance.

Predators:   Sweet Potato Sea Cucumbers are eaten by fish, crabs, and Western Gulls, Larus occidentalis.

Reproduction:  Sweet Potato Sea Cucumbers are gonochoric (male or female for life). They reproduce sexually through broadcast spawning and fertilization occurs externally. The eggs hatch into planktonic larva which eventually settle to the seafloor and metamorphose into juvenile sea cucumbers.

Ecosystem Interactions: The Sweet Potato Sea Cucumber has a commensal relationship (good for the invader; no value to negative value to the host) with two species of Pea Crab, Pinnixa barnharti and Opisthopus transversus. The Pea Crabs utilize the Sea Cucumber’s intestinal tract for food and shelter. They are also prone to attack by a tiny eulimid snail that has pointy white shell that drills a hole in the Sea Cucumbers skin, and then siphons off body fluids for its survival until the host finally dies.

Human Interactions:  Sweet Potato Sea Cucumbers have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern. 

Synonyms:  Liosoma arenicola and Molpadia arenicola.