Channeled Sea Star, Tethyaster canaliculatus

Channeled Sea Star, Tethyaster canaliculatus. Sea Star provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, November 2011. Pictured star wingspan: 16 cm (6.3 inches).

Phylogeny: The Channeled Sea Star, Tethyaster canaliculatus (A. H. Clark, 1916), is a member of the Astropectinidae Family of Starfish. The genus Tethyaster is one of twenty-six genera in the Astropectinidae Family, and there are seven species in the Tethyaster genus. They are known in Mexico as Estrella Acanalada.

Morphology:  Channeled Sea Stars are somewhat flattened, with a wide central disc and five narrow, tapering, arms that often differ in lengths. The plates along the margins of the arms are very obvious. 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. These stars may be mottled or solid colored with brown, orange, reddish-brown, or tan colors. Channeled Sea Stars can reach a maximum  of  50 cm (20 inches) in diameter.

Habitat and Distribution:  Channeled Sea Stars are found on, or just under, the surface of mud and sand substrates. They reside from the intertidal zone to depths up to 180 m (585 feet). They are a subtropical to tropical Eastern Pacific species. The Channeled Sea Star is found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Bahía Vizcaino, Baja California, along the central and northwest coasts of the Baja Peninsula and north of the Midriff Islands in the Sea of Cortez. Interestingly, there are two isolated pockets of this species. One is in the Coronado Islands off the coast of the northern Baja California; the other is around Consag Rock off San Felipe in the extreme northern portion of the Sea of Cortez.

Diet: Channeled Sea Stars are a poorly studied and documented species. Little is known about their diet. Other species in the Astropectinidae family prey on bivalves, carrion, crustaceans, detritus, gastropods, other sea stars, and sea urchins. Because they cannot extrude their stomachs, they must swallow their prey whole.

Predators: Little is know about the predation of Channeled Sea Stars. Juveniles are preyed upon by shore birds, crabs, fish and  other sea stars.

Reproduction: Channeled Sea Stars are gonochoric (male or female for life). Reproduction may be asexual 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. Asexual reproduction is by fission or fragmentation.

Ecosystem Interactions: In the small area where their ranges overlap, Channeled Sea Stars are known to be parasitized by the Cooper’s Nutmeg Shell, Cancellaria cooperii. Otherwise, the commensal, mutualistic and parasitic relationships of Channeled Sea Stars have not been documented.

Human Interactions:  Channeled Sea Stars have no 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:  Moiraster gigas, Sideriaster canaliculata and Tethyaster gigas