Spiny Sand Star, Astropecten armatus

Spiny Sand Star, Astropecten armatus. Collected from a tidal pool in the greater Los Cabos area, Baja Californa Sur, November 2015. Pictured stars wingspan: 17 cm (6.7 inches).

Phylogeny:  The Spiny Sand Star, Astropecten armatus (Gray, 1840), is a member of the Astropectinidae family of Astropectinid Starfish. The genus Astropecten is one of twenty-six genera in this family, and there are one hundred four species in this genus. They are also known as the Armored Sand Star and Comb Sand Star and in Mexico as Estrella Espinosa de Arena.

Morphology: Spiny Sand Stars are somewhat flattened, with a moderately wide disc. They have  five long  arms that taper to knob-like terminal plates.  The margins of the disc and arms are lined with spines and obvious plates. The underside of the arms are lined with pointed tube feet, which lack suckers. They use these tube feet, along with their spines to borrow under the surface of the soft sediments in which they live. The aboral (dorsal) surface of Spiny Sand Stars is covered with paxillae (small, umbrella shaped ossicles that form a watertight cavity housing the gills). They have sessile pedicellariae. The disk contains most of the organs, with the mouth on the ventral side and the madreporite (entry plate for the water vascular system) on the dorsal surface. They are unable to extrude their stomach like most other sea stars.  They may be gray, pink, orange, lavender, or brown in color. Spiny Sand Stars reach 36 cm (14 inches) in diameter.

Habitat and Distribution: Spiny Sand Stars are found on, or just under, the surface of sand, mud, and fine gravel. The combination of their pointy tube feet and marginal spines allow this species to move quickly over soft substrates. They live from the very low intertidal region to depths of, at least, 160 m (525 feet). Some sources extend the depth range to 302 m (990 feet). Spiny Sand Stars are a temperate and tropical Eastern Pacific species. In Mexican waters they are found along the entire Pacific coast, including the Gulf of California, the Tres Marias Islands, and the Revillagigedos Islands. They are probably the most abundant sea star in sandy habitats in Western Mexico.

Diet: Spiny Sand Stars are predatory carnivores that generally eat mollusks with the Purple Dwarf Olive Shell, Callianax biplicata, being its primary food source, but they also dconsume sand dollars, sea pansies, and dead fish. All prey is swallowed whole as they do not have the ability to extrude their stomachs.

Predators:  Spiny Sand Stars are a poorly studied and understood species. There is little documentation regarding predation of this species. Other species in this family are preyed upon by crabs and fish. They are most vulnerable in their juvenile stage.

Reproduction: Spiny Sea Stars are gonochoric (male or female for life). Reproduction may be asexual, by both regeneration and clonal, or sexual. Sexual reproduction involves broadcast spawning with external fertilization. The fertilized eggs hatch into planktonic larvae and later metamorphose into pentamerous juveniles which develop into young sea stars with stubby arms.

Ecosystem Interactions: Spiny Sand Stars are a poorly studied and understood species. The ecosystem interactions of this species have not been documented. Some species in this genus have commensal relationships with polychaetes. Also, endoparasitic crustaceans of the genus Dendrogaster parasitize species in Astropecten genus.

Human Interactions:  Spiny Sand Stars have little direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms:  None