Ophiocomella alexandri
A banded, spiny brittle star from the eastern Pacific.
Ophiocomella alexandri, also called Alexander's spiny brittle star or the banded brittle star, is a marine brittle star species. Theodore Lyman first scientifically described it in 1860, naming it for his friend Alexander E. R. Agassiz, who was the son of Lyman's mentor, Louis Agassiz.
This animal has five arms radiating from a central disk, giving it pentaradial symmetry. Its body is dark brown, with lighter gray bands on the upper arm surfaces that have hints of yellow. These colors shift daily, possibly as camouflage against predatory fish, similar to the banding pattern. Males and females look identical. The central disk is rounded, with small bumps on top, and can reach up to 25.2 millimeters (0.99 inches) across. It houses the mouth, digestive system, and gonads. The arms are highly flexible, and when stretched straight, the brittle star can span up to 450 millimeters (18 inches). As the common name suggests, the arms are very spiny, with five to seven long spines on each lateral plate.
The species lives from the intertidal zone down to 70 meters (230 feet) deep. It is benthic, dwelling on the seafloor, and prefers rocky bottoms and coral reefs. Its range covers the eastern Pacific Ocean from southern California to Colombia, including the Gulf of California, and it is also found in the Galapagos Islands.
Alexander's brittle stars reproduce by broadcast spawning. They are gonochoric, with separate male and female individuals in roughly equal numbers. Males release sperm and females release eggs into the water, where fertilization occurs. The resulting zygotes develop into free-swimming pluteus larvae. This species feeds on detritus, and there is evidence that it catches and eats small fish in aquariums.
Quick Facts
- Taxon
- Ophiocomella alexandri
Facts from the source article.
Lore & Background
This brittle star is pentaradially symmetric with five arms attached to a central disk. It is dark brown with lighter bands on the upper side of the arms; the lighter parts are gray with hints of yellow. The colors change on a daily cycle, which, like the banding, may be a form of camouflage to hide from predatory fish. Males and females are identical in appearance. The central disk is rounded with small bumps on its upper side and can be up to 25.2 mm across. It contains the mouth, digestive system, and gonads. The arms are very flexible, and when straight give the brittle star a diameter of up to 450 mm. As its common name suggests, the arms are quite spiny, with five to seven long spines on each lateral plate. The species lives from the intertidal zone to a depth of 70 meters, on rocky bottoms and coral reefs, in the eastern Pacific from southern California to Colombia, including the Gulf of California and the Galapagos Islands. It reproduces by broadcast spawning and is gonochoric, with approximately equal numbers of males and females. Zygotes develop into free-swimming pluteus larvae. It feeds on detritus, and there is evidence that these brittle stars catch and eat small fish in aquariums.
Reader's Guide
Ophiocomella alexandri is notable for its distinctive banded appearance and daily color changes, which may serve as camouflage against predatory fish. Its description by Theodore Lyman in 1860 connects it to the prominent Agassiz family of naturalists, as it was named for Alexander E. R. Agassiz. The species exhibits typical brittle star anatomy with pentaradial symmetry and spiny arms, and its size—up to 450 mm in diameter—makes it a relatively large brittle star. Its distribution along the eastern Pacific from southern California to Colombia, including the Galapagos Islands, and its habitat on rocky bottoms and coral reefs, define its ecological niche. The species is gonochoric and reproduces via broadcast spawning, with free-swimming larvae. While primarily a detritivore, there is evidence it may also catch small fish in aquariums, suggesting opportunistic feeding behavior. The equal sex ratio and lack of sexual dimorphism are also noted.
More in Sea Cucumbers and Brittle Stars, Part 3 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced