Ophiactis savignyi

Background

Ophiactis savignyi was first described in 1842 by the German zoologists Johannes Peter Müller and Franz Hermann Troschel. The specific name honors the French zoologist Marie Jules César Savigny.

The disc is up to 5 mm in diameter, with a pale greenish-brown aboral surface covered by large overlapping scales and a scattering of spines. The six arms are long, slender, and tapering, each segment bearing five or six thorny spines. The oral surface is cream-colored.

This brittle star has a near cosmopolitan distribution in warm seas, occurring in the western Indo-Pacific, eastern Pacific, and on both sides of the Atlantic. Populations in the Pacific and Atlantic were only united after the Panama Canal was cut in 1914. It is found from the intertidal zone down to about 500 meters, in reefs, mangroves, seagrass meadows, among seaweeds, and in contaminated waters, often living inside sponges possibly as a commensal.

O. savignyi is a deposit feeder and scavenger, feeding on detritus. It raises arm tips to detect food, rolls nutritious items into a ball, and moves them to the mouth using tube feet. Stomach contents have included bryozoans, foraminiferans, and gastropods among detritus and sand grains.

Individuals are either male or female and can reproduce sexually or asexually by fragmentation. In Taiwan, mature gametes occur from March to December, with peak spawning in May and June; fission occurs mostly between July and December. Sampling found 48% of individuals were regenerating, and the sex ratio was 24 males per female.