Caudinidae Family of Sea Cucumbers

Sweet Potato Sea Cucumber, Caudina arenicola. A representative of the Caudinidae Family of Sea Cucumbers.

Phylogeny:  The Caudinid Sea Cucumbers are members of the Caudinidae Family and like Starfish and Sea Urchins belong to the Phylum Echinodermata and the Subphylum Echinozoa.  They are characterized by a larval stage with bilateral symmetry and an adult stage with radial (5-rayed) symmetry. They lack the tube feet of other echinoderms. They belong to the Class Holothuroidae the Order Molpadida.

Distribution: The Caudinid are found worldwide in marine environments of temperate tropical and polar seas. There are currently sixty-five known members of the Caudinidae Family of which  three are found along the Pacific coast of Mexico. The adults are benthic.

Morphology:  The Caudindid are unsegmented and their disc may be cucumber, sphere or star shaped. They lack arms, and they have a soft body with branched, unbranched or pinnate tentacles around their mouth utilized to capture food. They have smooth, or slimy, skin with fine to large papillae (projections). They have a water vascular system, tube feet, and a complete digestive system, but they lack eyes, a head, nervous system, or excretory system. They are primarily burrowers  that possess  an internal madreporite (perforated plate covering entry port of water vascular system) to keep it out of the sediment. They primarily consume dentris and diatoms. In turn they are preyed upon by crabs, crustaceans, fish, starfish, and sea turtles. They vary in color and pattern, but most are black, brown, or greenish.

Ecosystem Roles: The Caudinidid are perhaps the most sedentary of all the sea cucumbers. Molpadiidae Sea Cucumbers are found under and within rocks, rubble, and sand subtidally and to depths exceeding 5,200 m (17,056 feet). Most species are found at depths greater than 100 m (328 feet). They spend the majority of their life cycle in their burrow. They are active nocturnally. They are surface and subsurface depositional detritivores that feed by filtering food from the surrounding water, and others are depositional feeders, gathering food from the surface of the substrate. Some filter sand through their digestive tracts, removing food from the sand as it passes through.  In  turn they are preyed upon by crabs, fish, gastropods, marine animals, and sea stars. They vary in size, from small to over 60 cm (2 feet 0 inches) in length. They may also play host to several species of commensal, or parasitic, crustaceans and mollusks. Some species of Molpadiidae Sea Cucumbers are the subject of commercial fisheries and aquaculture operations. They are considered a food source and a source of pharmacological agents.

Reproduction:  The Caudinidid individuals are either male or female and they reproduce sexually with fertilization occurring externally. The embryos develop in to planktonic larvae and then doliolaria (barrel-shaped stage) before becoming juvenile sea cucumbers.