Asterodiscidae Family of Sea Stars

Two Sea Stars of the Asterodiscidae Family can be found in this website:

Phylogeny: Asterodiscididae Sea Stars, like sea urchins and sea cucumbers, are in the phylum Echinodermata. Echinoderms (meaning spiny skin) are characterized by a larval stage with bilateral symmetry and an adult stage with 5-rayed radial symmetry. They are unsegmented and can be cucumber, disc, sphere or star in shape. They have a water vascular system, tube feet, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. They are found only in marine environments. Asterodiscididae Sea Stars are in the class Asteroidea, which is characterized by having a flattened, star shape. There is a central disc, surrounded by multiple (5-40) radiating arms (or rays). The disc contains most of the organs, with the mouth on the ventral side and the anus and madreporite (entry plate for the water vascular system) on the dorsal surface. Asteroidea Sea Stars are one of two major classes of Astereozoans. The other class is Ophiuroidea.  Asteroideans are easily distinguished from Ophiuroideans by the arms of Asteroideans having a broad attachment point where the arms join the disc. Their arms taper as they extend from the disc. Ophiuroideans have arms that are relatively the same thickness their entire length, giving them a narrow attachment point at the disc. All Asteroideans have the ability to regenerate amputated limbs. The Asterodiscididae Family is one of fifteen families in the order Valvatida. The Asterodicididae Family contains five genera and twenty-two species. These sea stars are commonly known as Asterodiscids.

Morphology: Asterodiscids generally have five arms, with two rows of tube feet on the underside of each arm. The tube feet have suckers. They have conspicuous ossicles (calcareous particles that are part of the endoskeleton) along their margins. Some species in this family have paxillae (small, umbrella shaped ossicles that form a watertight cavity housing the gills). Some species in this family have clamp-like pedicellariae (pincers) that are housed within the skeletal plates. Sea stars in this family may be brightly colored, and they range in size from only a few millimeters to a maximum of 75 cm (29.3 inches) in diameter.

Habitat and Distribution: Asterodiscids may be found on rock, coral, sand, or mud. They live intertidally, and to depths exceeding 800 m (2,625 feet).  They are found worldwide in tropical to temperate seas. Two species from the Asterodiscidae Family are found in Mexican waters.

Reproduction: Asterodiscids may be either gonochoric or simultaneous hermaphrodites. The reproduce sexually, through broadcast spawning, with external fertilization. They can also reproduce asexually through regeneration.

Ecosystem Interactions: Very little is documented regarding the behaviors of Asterodicids.  It is thought that they feed on bivalves, crustaceans, and gastropods. In turn they are preyed upon by shore brids, crabs and fish.