Spiny Basket Sea Star, Astrocaneum spinosum

Spiny Basket Sea Star, Astrocaneum spinosum. Basket Sea Star provided by the commercial fishermen in the greater Los Cabos area, Baja California Sur, June 2009. Size: 15 cm (5.9 inches). Fairly common and found in the branches of the Red Gorgonian, Eugorgia daniana. Identification courtesy of Dr. Richard Brusca, Tucson, Arizona.

Phylogeny:  The Spiny Basket Star, Astrocaneum spinosum (Lyman, 1875), is a member of the Gorgonocephalidae family of Basket Stars. The genus Astrocaneum is one of thirty-two genera in this family, and there are two species in this genus. They are known in Mexico as Estrella Canasta Espinosa.

Morphology: Spiny Basket Stars have radial symmetry, a flattened central disk, and five arms. The arms have tube feet on their underside, but unlike the tube feet of sea stars, these feet lack suction cups. Their five arms branch repeatedly, into many dozens of arms. The branches change from Y- shaped to alternating (left/right) as you move away from the disk. The arms have 5-6 spines along their mid-line and each arm is tipped with a barb. The upper surface of each arm is leathery and granular. There is a mouth on the underside of the disk and consists of five “jaws”. Spiny Basket Stars cannot extend their stomach out though their mouth to digest prey externally. They use their arms and tube feet to pass prey into their mouth. Spiny Basket Stars are highly mobile, using their arms to walk and climb. They can be beige, tan, or brown in color. Spiny Basket Stars reach 13 cm (5.1 inches) to 26 cm (10 inches) in diameter.

Habitat and Distribution:  Spiny Basket Stars are found on gorgonians and over rubble, sand, or mud at depths between 9 m (30 feet) and 183 m (600 feet). They are fairly delicate and need to stay deep enough to avoid strong wave action. Spiny Basket Stars are a tropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean from Punta Eugenia, Baja California Sur south to Guatemala. They are found throughout the Sea of Cortez.

Diet:  Spiny Basket Stars feed by climbing high on to gorgonians and extending their many arms to form a net. This net captures small prey that is being swept by in the current.  Once the prey is grasped by the barbs, it is encased in mucous and then passed to the mouth. Prey includes planktonic crustaceans, fish larvae, worms, and jellies. They feed primarily at night.

Predators: There is limited documentation related to the predators of Spiny Basket Stars. Other species in this genus are primarily eaten by crustaceans and fish. As a defense mechanism Spiny Basket Stars can roll their arms into a tight ball making it it difficult for predators to nip at small arm tips. They also use this technique to avoid being swept away by strong currents.

Reproduction: Spiny Basket Stars are gonochoric (male or female for life). Reproduction is sexual, with external fertilization. The embryos develop in bursae, which act as brood chambers where the embryos develop into juveniles and later crawl out from the bursal slits. After their planktonic larval stage they metamorphose into basket stars and settle to the bottom.

Ecosystem Interactions:  Spiny Basket Stars are a poorly studied and poorly understood species. There is no documentation of their involvement in commensal, parasitic, or symbiotic relationships.

Human Interactions: Spiny Basket Stars are one of the top thirty invertebrate species targeted by the aquarium trade in Mexico. Over collection have caused the decline of local populations is some regions. 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:  Astrophyton spinosum.