Sweet Potato Sea Cucumber

Sweet Potato Sea Cucumber, Molpadia arenicola

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

The Sweet Potato Sea Cucumber, Molpadia arenicola (Stimptson, 1857) is a member of the Molpadiidae Family of Sea Cucumbers, and is also known as the Sea Sweet Potato.

The Sweet Potato Sea Cucumber has a thick fusiform body with leathery skin that has a smooth surface without hair and suckers. They are mottled orange in color. They have 15 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 that minutely pinnate toward the extremities. The oral ring is composed of 5 slender pieces projecting and branched below and notched above. They do not have tube feet or elongated tentacles. The Sweet Pea Sea Cucumber reach a maximum length of 16.5 cm (6.5 inches) as documented by the animal photograph above.

The Sweet Potato Sea Cucumber resides partially buried in muddy and sandy coastal habitats and may burrow to depths up to 40 cm (16 inches) but normally resides near the surface. They have mobility but are exceedingly slow moving. They feed by ingesting sand on a continuous basis and they remove and consume the associated microbes and detritus. The retain a large amount of sand within their body at all times affording them with an inflated appearance. The Sweet Potato Sea Cucumber has a commensal relationship (good for the invader; no value to negative value to the host) with the Pea Crab as the Pea Crab utilizes 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.

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.

From a conservation perspective the Sweet Potato Sea Cucumber has not been formally evaluated. They are found occasionally along the beaches of Southern California and are easily located by following their highly visible tracks.

Synonyms are Caudina arenicola and Liosoma arenicola.