Echinodermata Family of Sea Cucumbers

Phylogeny:  Sea Cucumbers of the Holothuriidae Family, like Starfish and Sea Urchins are in the Phylum Echinodermata and the Subphylum Echinozoa. They are in the Class Holothuroidae and the Order Holothuriida.

Distribution:  The Holothuriidae are found worldwide in temperate and tropical seas. They are found only in marine environments. There are currently two hundred known members of the Echinodermata Family of which twenty-five are found along the Pacific Coast of Mexico. They are found on, under and within rocks, rubble, and sand from the intertidal zone to depths that exceed 300 m (984 feet).

Morphology:  The Holothuriidae are unsegmented and their disc may be cucumber, sphere or star shaped. They have skin that has fine to large papillae (projections), and are characterized by a larval stage with bilateral symmetry and an adult stage with radial (5-rayed) symmetry. They lack arms, and they have a soft body wall and branched tentacles around their mouth utilized to capture food. The tentacles around their mouth are flattened, and often leaf-like. Their body wall is thick and leathery, with ossicles (tiny, calcified rods or tables under the skin) and their tube feet form a noticeable sole, and they may be spherical or elongate in shape.  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 also vary in size, from small, to over 60 cm (2 feet 0 inches) in length. They vary in color and pattern, but most are black, brown, or greenish.

Ecosystem Roles:  The Holothuriidae are active nocturnally. Some species are suspension feeders, 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. They primarily eat detritus and diatoms. In turn they are preyed upon by crabs, crustaceans, fish, starfish, and sea turtles. Holothuriidae larvae are planktonic, but the adults are benthic. Sea Cucumbers in this order may have one of two unique defense mechanisms. Some species can shoot sticky white threads (Cuvierian tubules) out of their anus, which may entangle or distract predators, allowing the Sea Cucumber to escape. Other species can eviscerate themselves by shooting their internal organs out of their anus, again, distracting a predator. The Sea Cucumber have the ability to quickly regrow a new digestive tract.

Reproduction:  Holothuriidae are either male or female, and fertilization takes place externally. Their larvae is planktonic and the adults are benthic.