Echinasteridae Family of Sea Stars

Thin-spined Sea Star, Echinaster tenuispinus. A representative of the Echinasteridae Family of Starfishes.

Phylogeny: The Echinasterid Sea Stars are members of the Echinasteridae Family of Starfishes and are in the Phylum Echinodermata, a large Phylum that includes Brittle Stars, Sea Cucumbers, Sea Lilies, Starfish and Urchins. They are found in marine environments. Echinasterid Sea Stars are in the Class Asteroidea and the Order Spinulosida.

Distribution: Echinasterids have a cosmopolitan distribution and are found from tropical to polar seas. The Echinasteridae Family has one hundred thirty-six species of which eight are found along Mexico’s Pacific Coast. They reside on gravel, mud, rock and sand substrates. They normally live intertidally but can be found at depths up to 1,000 m (3,330 feet).

Morphology:   Echinasterids have a central disc that is surrounded by 5 radiating arms with a broad attachment point where the arms join the disc that have are long and tapering with a circular cross section with a flattened body that is unsegmented and are cucumber, disc, sphere or star in shape. They  have a spiny aboral (dorsal) surface with aboral reticulate (net-like) plates with ambulacral grooves that have fine or conical, cylindrical or thorny spines. They have a water vascular system, tube feet with a singular ampulla and a pass through small pores, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. 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. Their mouths are surrounded by triangular plates and these stars lack the pedicellariae found in other sea star families. They have a unique water vascular system that uses hydraulic power to operate a multitude of tiny tube feet that are used in locomotion and food capture. They feed via inserting the stomach out through the mouth surrounding the prey, secreting enzymes to digest the food and then retracting the stomach when finished eating. They are characterized by a larval stage with bilateral symmetry and an adult stage with 5-rayed radial symmetry. All Echinasterids have the ability to regenerate amputated limbs. Starfish in this family can reach 30 cm (12 inches) in diameter.

Ecosystem Roles:  Echinasterids have diverse diets and feeding styles grazing on algae, bryozoans, and sponges, or they may be predators feeding on hydroids, sea cucumbers, sea pens, other sea stars, sea urchins, and tunicates. In turn they are preyed upon by shore birds, crabs, fish, marine mammals and other sea stars.

Reproduction:  Reproduction occurs via broadcast spawning.