Ophiothrix spiculata, commonly known as ‘western spiny brittle star‘, is a species of echinoderm belonging to the class Ophiuroidea, order Ophiurida and family Ophiothricidae. The genus name ‘Ophiothrix‘ comes from the Greek ‘ophis‘ meaning snake, and ‘thrix‘ meaning hair, referring to the long, flexible arms reminiscent of snakes. ‘Spiculata‘ derives from the Latin ‘spicula‘ meaning thorn, due to the presence of numerous spines on its arms. This species is widely distributed along the eastern Pacific coast from northern California to Peru, and is common in rocky reef habitats, soft bottoms and areas with hard substrates, between the intertidal zone and depths of up to 30 meters.
Ophiothrix spiculata has a small, rounded central disk that can reach up to 2 centimeters in diameter, from which extend five long, slender arms that can measure up to 15 centimeters in length each. These arms are extremely flexible and are covered with thin spines, which can vary in color from white to brown or even purple. The body of the spiny brittle star can exhibit colors ranging from bright red to orange, yellow, green or brown, and usually has a mottled or banded pattern. The arms are segmented and each segment is covered with small movable spines that aid in locomotion and the capture of food particles. Ophiothrix spiculata differs from similar species, such as Ophiothrix suensonii, by having longer and less dense spines, as well as a more distinctive and varied color pattern.
As for its diet, Ophiothrix spiculata is a filter-feeder and detritivore. It feeds mainly on organic particles, phytoplankton, detritus and small prey that it captures using its spine-covered arms. The brittle star extends its arms into the current to capture food particles, which are transported to the mouth, located at the bottom of the central disk, by coordinated movements of the spines. This feeding mode allows Ophiothrix spiculata to take advantage of water currents to efficiently obtain nutrients.
Reproduction of Ophiothrix spiculata is both sexual and asexual. Sexual reproduction takes place through the release of gametes into the water, where external fertilization occurs. Larvae are planktonic and go through several developmental stages before settling on the substrate and metamorphosing into juveniles. This species can also reproduce asexually by fission, where the body splits into two parts and each fragment regenerates the rest of the body. This method of asexual reproduction is common under favorable conditions and allows the population to rapidly increase in numbers.
An interesting fact about Ophiothrix spiculata is its ability to regenerate the arms it loses, a strategy it uses to escape predators. This ability to regenerate is a common feature among echinoderms, but Ophiothrix spiculata is especially notable for the speed with which it can do so. In addition, it often forms large aggregations in places where the current is favorable for food filtration, which can have a significant impact on the dynamics of the local ecosystem by contributing to the scavenging of suspended particles in the water. This species can also be found in symbiosis with sponges and other invertebrates, taking advantage of the protection and water flow offered by their hosts.
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