Asteriidae Family of Sea Stars

Phylogeny: The Asteriidae Sea Stars or Asteriids are members of the Asteriidae Family of Sea Stars, and like Sea Urchins and Sea Cucumbers, belong to the Phylum Echinodermata. They are in the Class Asteroidea and the Order Forcipulatida.

Distribution:  Asteriids are found over and within mud, rock or sand substrate from the intertidal zone to depths up to 1, 200 m (3,900 feet). They are found worldwide in tropical, temperate and sub-polar waters. There are presently one hundred and twenty-three known species in the Asteriidae Family; only nine are found along the Pacific Coast of Mexico.

Morphology:  Asteriids are characterized by having a flattened, star or pentagonal shaped body. There is a central disc, surrounded by five to forty 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. They lack a sharp differentiation between the ventral and dorsal sides of the disc and arms and have crossed pedicellariae (tiny pincers) on their dorsal surface, as well as single or grouped spines. Their tube feet lack a sucking disc. They are known for their spiny skins and 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 shaped. They have a water vascular system, tube feet, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. The water vascular system has diverse functions, including locomotion, gas exchange, and nutrient circulation. Asteriids are further defined by having a mesh-like aboral skeleton. Asteroideans are easily distinguished from Ophiuroideans by having a broad attachment point where the arms join the disc and arms that taper as they extend from the disc. Ophiuroideans have arms that are relatively the same width their entire length, giving them a narrow attachment point at the disc. All Asteroideans have the ability to regenerate amputated limbs. They can be found in a variety of colors including blue, brown, orange, purple, reddish, and yellow. The largest Asteriids may reach 1.00 m (3 feet 3 inches) in diameter. They are found only in marine environments.

Ecosystems Role:  Commencing in 2013, most Asteroidean species in the Temperate Eastern Pacific have seen dramatic drops in their populations, which has been as high as 80% for some species. The decline is attributed to Sea Star Wasting Disease, a Densovirus (Parvoviridae). It is unknown if this Densovirus is the cause of the high mortality or if it is a symptom of other causes such as environmental stressors. Only recently have some species begun to recover, and only within selected regions. From a conservation perspective the Sunflower Star, Pycnopodia helianthoides, is currently considered to be Critically Endangered. Asteriids are predators eating a variety of prey animals including: amphipods, other astriids, barnacles, bivalves, chitons, crabs, gastropods, isopods, polychaetas, sand dollars, sea cucumbers, and sea urchins; they may also scavenge dead carrion.  They feed by grabbing prey with their sucker covered arms and passing the prey to their mouth. They may swallow their prey whole, or evert their stomach and digest the prey externally. In tern Asteriids are preyed upon by shore birds, crabs, and marine mammals.