Ophioderma longicauda, the Smooth Brittle Star (a.k.a. Snake Brittle Star or Brown Brittle Star), is a type of Brittle Star. These are echinoderms in the class Ophiuroidea closely related to starfish.
Brittle Stars or ophiuroids crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm in length on the largest specimens. They are also known as serpent stars; the New Latin class name Ophiuroidea is derived from the Ancient Greek ὄφις, meaning “serpent”.
The genus Ophioderma belongs to the family Ophiodermatidae, order Ophiurida, class Ophiuroidea, phylum Echinodermata and kingdom Animalia.
The Smooth Brittle Star is common on the Eastern Atlantic Ocean and widely spread in the seas around Malta in the Mediterranean Sea. It lives in dark places, on rocky or sandy ground, from a couple of metres depth down to 100 metres. Its colour varies from red to green to dark brown, almost black, sometimes orange on deep specimens. It is a sciaphilic species, living under rocks or preferring to take refuge in cracks or crevices, even very quickly if disturbed.
The ophiuroids diverged in the Early Ordovician, about 500 million years ago. Of all echinoderms, the Ophiuroidea may have the strongest tendency toward five-segment radial (pentaradial) symmetry. The body outline is like that of starfish, in that ophiuroids have five arms joined to a central body disk. However, in ophiuroids, the central body disk is sharply marked off from the arms.
The disk contains all the viscera. That is, the internal organs of digestion and reproduction never enter the arms, as they do in the Asteroidea. The underside of the disk contains the mouth, which has five toothed jaws formed from skeletal plates. The madreporite is usually located within one of the jaw plates, and not on the upper side of the animal as it is in starfish.
The ophiuroid coelom is strongly reduced, particularly in comparison to other echinoderms. Suckers and ampullae are absent from the tube feet.
Most ophiuroids have no eyes, or other specialised sense organs. However, they have several types of sensitive nerve endings in their epidermis, and can sense chemicals in the water, touch, and even the presence or absence of light. Moreover, tube feet may sense light as well as odours. These are especially found at the ends of their arms, detecting light and retreating into crevices.
Smooth Brittle Stars generally sexually mature in two to three years, become full grown in three to four years, and live up to 5 years. Ophiuroids can readily regenerate lost arms or arm segments unless all arms are lost. Ophiuroids use this ability to escape predators, in a way similar to lizards which deliberately shed the distal part of their tails to confuse pursuers. Discarded arms have not been shown to have the ability to regenerate.
Ophioderma longicauda use their arms for locomotion, moving rapidly by wriggling their arms which are highly flexible and enable the animals to make either snake-like or rowing movements. However, they tend to attach themselves to the sea floor or to sponges or cnidarians, such as coral. They move as if they were bilaterally symmetrical, with an arbitrary leg selected as the symmetry axis and the other four used in propulsion. The axial leg may be facing or trailing the direction of motion, and due to the radially symmetrical nervous system, can be changed whenever a change in direction is necessary.
The photo of this Smooth Brittle Star was taken at a depth of 5 metres at Reqqa Point on Gozo’s north coast.
Photo taken by Brian Azzopardi