Nine-armed Sea Star, Luidia senegalensis

Nine-armed Sea Star, Luidia senegalensis. Sea star collected off of Tigertail Beach, Marco Island, Florida, January 2019. Size: 32 cm (13 inches).

Phylogeny:  The Nine-armed Sea Star, Luidia senegalensis (Lamarck, 1816), is a member of the Luidiidae family of Sea Stars. The genus Luidia is the only genus in this family and has  forty-nine species. In Mexico they are known as  Estrella de Mar de Senegal.

Morphology: The Nine-armed Sea Star has a relatively small disk that is circular in outline. Radiating from this disk are nine, long, thin, tapering, arms. The aboral (dorsal) surface is covered with square to irregularly shaped plates. The plates on the disk, and running down the center of each arm, are gray. The plates along the margins of the arms are cream to yellow in color, and spiny. The oral surface is whitish. The tube feet are transparent and lack suckers. Nine-armed Sea Stars reach a maximum of 40 cm (16 inches) in diameter.

Habitat and Distribution:  Nine-armed Sea Stars are found in calm waters, such as lagoons and bays. They live on soft substrates, including sand and mud. Nine-armed Sea Stars are found subtidally, and to depths up to 46 m (151 feet). This is a tropical Western Atlantic species and found in all Mexican waters including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.

Diet: Nine-armed Sea Stars feed by traveling through the substrate and preying on brittle stars, crustaceans, small mollusks and polychaetes. They also feed on detritus by ingesting substrate and filtering out organic matter. They lack an anus so undigested matter is passed out through the oral opening.

Predators: Nine-armed Sea Stars are a poorly studied and understood species. Documentation of their predators is limited to the genus level. Other species in this genus are consumed by crabs, fish and other sea stars.

Reproduction: Nine-armed Sea Stars are gonochoric (male or female for life). Reproduction can be asexual, through regeneration or cloning, or sexual. Sexual reproduction is accomplished through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae, which later settle to the bottom and metamorphose into pentamorous juveniles. These juveniles develop into young sea stars with stubby arms.

Ecosystem Interactions: The polychaete Podarke obscura sometimes lives in the ambulacral grooves of Nine-armed Sea Stars. The nature of this relationship has not been documented.

Human Interactions: Nine-armed Sea Stars have a very limited impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a wide distribution and should be consider to be of Least Concern.

Synonyms:  Asterias senegalensis and Luidia marcgravii.