Banded Brittle Star, Ophiocomella alexandri

Banded Brittle Star, Ophiocomella  alexandri. A very common brittle star collected from a tidal pool in the greater Los Cabos area, Baja California Sur, January 2016. Wing span: 15 cm (5.9 inches).

Phylogeny: The Banded Brittle Star, Ophiocomella alexandri (Lyman 1860), is a member of the Ophiocomidae Family of Brittle Stars that has two subfamilies, Ophiocominae and Ophiopsilinae that have four genera and one hundred twenty-seven species and one genera with thirty species, respectfully. The Ophiocoma Genus has seventy-seven known species. They are also known as Alexander’s Spiny Brittle Star and in Mexico as Estrella Quebradiza Rubí.

Morphology: This echinoderm has a rounded central disk with five lobes and rounded oral plates. The long slender arms stem out from in between the lobes. This organism typically has five arms, but this number can vary from four to six depending on stage of arm regeneration. The arms are gray with dark brown banding and five to seven stout, blunt spines on each lateral plate that are perpendicular to the arm axis. The aboral or dorsal surface of the disk has a uniform light brown coloration and is covered with minute granules giving it a sandpaper feel. The ventral side is a uniform color without banding. Their color can changes as the day progresses to various shades of black, brown, and gray. Their central disk can reach a maximum of 2.5 cm (1.0 inch) in diameter; the arms can reach a maximum of 44 cm (17.5 inch) in length.

Distribution: The Banded Brittle Star is a benthic organism that favors rocky shores. They are found under rocks and in sand or mud. They live from the lower intertidal zone to depths up to 70 m (230 feet). Banded Brittle Stars are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean. They are normally mixed in with the Black Spiny Brittle Star, Ophiocoma aethiops.

Diet: Banded Brittle Stars are predators and scavengers that eat detritus, small fish, mollusks, plankton, and worms.

Predators: Banded Brittle Stars are preyed upon by crabs, fish, and sea stars.

Reproduction: The Banded Brittle Star reproduces via broadcast spawning. Fertilization occurs externally through the water, producing zygotes that develop into free-swimming pluteus larva. This results in distinct male and female sexes in equal numbers, known as gonochoric reproduction.

Ecosystem Interactions: Banded Brittle Stars are a poorly studied and understood species. There is no documentation of commensal, parasitic or symbiotic relationships.

Human Interactions: Banded Brittle 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 relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Ophiocoma alexandri.