Astropectinidae Family of Sea Stars

Phylogeny: The Astropectinid Sea Stars or Astropectinids are members of the Astropectinidae 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 Paxillosida. Asteroidea Sea Stars Ophiuroidea are the two major Classes of Astereozoans.  Asteroideans are easily distinguished from Ophiuroideans as their arms have a broad attachment point where the arms join the disc and 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. The Paxillosida Order is characterized by having only one larval phase, compared to the two phases of other Orders in this Class. 

Distribution:  Astropectinids are found on and within soft sediments such as sand and mud that affords them camouflage from predators. They are found intertidally to depths that exceed 3,200 m (10,500 feet). The Astropectinid Sea Stars are found worldwide in tropical, temperate, and polar seas. There are two hundred forty-three species placed into twenty-three Genera in the Astropectinid Family of which  ten species are found along Mexico’s Pacific Coast.

Morphology:  Astropectinids 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) that taper to knob-like terminal plates. Their marginal plates are block-like, granular  or spiny in texture, and covered with spines. These spines, projecting from the margins, may have a comb-like appearance, leading to the common name Comb Stars. The aboral (dorsal) surface of these Sea Stars is covered with paxillae (small, umbrella shaped ossicles that form a watertight cavity housing the gills). 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 have large mouth angle plates comprised of fused ambulacral ossicles. They have a water vascular system, tube feet, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system lacking an anus and the ability to extrude their stomach like most other sea stars. The water vascular system has diverse functions, including locomotion, gas exchange, and nutrient circulation. They have sessile pedicellariae. Their tube feet are pointed and lack suckers. They use these tube feet, along with their spines to burrow under the surface of the soft sediments in which they live. They 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. Most species in this family have fairly drab coloration, but some species have bright colors including orange, purple, and red.  Astropectinids can reach up to 55 cm (22 inches) in diameter. They are found only in marine environments.

Ecosystems Role: Astropectinids prey on bivalves, carrion, crustaceans, detritus, gastropods, sea urchins, and other sea stars. Because they cannot extrude their stomachs, they must swallow their prey whole. In turn they are preyed upon by crabs and fish. Commencing in 2013, most Asteropectinid 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.