Ophiuroidea – Brittle Stars
The Brittle Stars are a class in the phylum of the Echinodermata. The Ophiuroidea contain more than 2000 species, of which more than 1200 live deeper than 200m. The scientific name is derived from the Greek “ophis” for snake and “ura” for tail.
In contrast to many starfish, the central disc of the Brittle Stars is more clearly recognizable. From it almost always five thin arms are going off. The mouth is at the bottom and at the same time serves as an anus.
Ophiuroidea lack the suction cups on the feet. Instead, they crawl forward by means of arm movements.
In their epidermis, they have sensitive nerve cells that react to chemicals, touch and light.
Like starfish, Brittle Stars have a good regeneration capacity. If an enemy bites an arm off, it grows again rapidly.
Habitat and Distribution
The Brittle Stars are ground-dwellers, and reach to depths over 6000m. They are found both on rocky and muddy ground, in coral reefs and sea grass meadows.
Their distribution ranges from the Poles to the tropical seas. One can say that they are spread around a depth of 20m world wide.
Ophiuroidea, depending on the species, feed on carrion, detritus, algae, plankton, small crustaceans and worms.
Most species of Brittle Stars have separated sexes, although there are hermaphrodites and some even change the sex in the course of their lives.
Fertilization takes place externally in species of the more tropical zones, while in the polar regions there are many species that carry out brood care. In addition, some can reproduce asexually by dividing themselves.
Ophiuroidea are sexually mature with about 2 to 3 years. Their life expectancy is about 5 years, of course there are representatives who are much older.
In the Mediterranean there are occurrences of up to 10000 individuals per m²!
It is known that over 60 species bioluminize.
The arms of the Ophiuroidea are very fragile and therefore they are thrown off completely or partially at the smallest touch.