Spiny Sea Star, Amphiaster insignis

Spiny Sea Star, Amphiaster insignis. Pictured star’s wingspan: 12.5 cm (4.9 inches). Exceedingly rare. Identification courtesy of Dr. Chris Mah, Smithsonian Institute, Washington, D.C.

Phylogeny:  The Spiny Sea Star Amphiaster insignis (Verrill, 1868), is a member of the Asterodiscididae family of Asterodiscid Sea Stars. The genus Amphiaster is one of five genera in this family, and this is the only species in this genus. They are known as the Red Spiny Sea Star and in Mexico as Estrella Espinosa.

Morphology:  Spiny Sea Stars have a wide central disk and five, short, triangular arms. The arms have a broad attachment point at the disk. There are two rows of tube feet, with suckers, on the underside of each arm. They have conspicuous ossicles (calcareous particles that are part of the endoskeleton) along their margins. The disk 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. Numerous, sharp, conical spines cover the dorsal (aboral) and marginal surfaces of the disc and arms. They are reddish-orange to reddish-brown in color. The spines may be pale orange, tan, reddish-orange, reddish-brown, or black in color. Spiny Sea Stars reach 17.4 cm (6.9 inches) in diameter.

Habitat and Distribution: Spiny Sea Stars are found on sand and mud, intertidally to depths up to of 128 m (420 feet). They are a tropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean from Magdalena Bay, Baja California Sur, south to Guatemala, including the entire Sea of Cortez and the Revillagigedos Islands.

Diet:  Spiny Sea Stars are a poorly studied and understood species. There is very little documentation regarding their diet. There is some speculation that they feed on the Crassa Brittle Star, Ophiolepis crassa, based on the fact that they share the same habitat. Other species in this family feed on bivalves, crustaceans and gastropods.

Predators:  Spiny Sea Stars are poorly studied. There is no documentation regarding predation for this species. Other species in this family are preyed upon by shore birds, crabs and fish.

Reproduction:  Spiny Sea Stars are gonochoric (male or female for life). They reproduce sexually through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae. The larvae start life in a bilaterally symmetrical form and in adulthood gain their radial symmetry. They are in their larval form for a few weeks before beginning their benthic life.

Ecosystem Interactions:  Spiny Sea Stars are poorly studied. There is no documentation of Spiny Sea Stars engaging in any types of commensal, parasitic, or symbiotic relationships.

Human Interactions: Spiny Sea Stars have no direct impact on human activities. From a conservation perspective they have not been formally evaluated. While they have a wide distribution, that are not common and there is insufficient data to assess their population status.

Synonyms:  None