Purple Starfish, Ophidiaster ophidianus, is a species of starfish from the East Atlantic (from mainland Portugal and the Azores down to the Gulf of Guinea) and the Mediterranean Sea. It has a big variation in colour (from red to orange) and may present brown spots. The central disc is small, covered by irregular plates, and the arms are thinner near the central disc. Each arm has lines of respiratory papillae. It can reach 40 cm in diameter.
Ophidiaster ophidianus belongs to the phylum Hechinodermata and to the class of Asteroidea and to the family Ophidiasteridae. This video was shot in Pantelleria in the Sicilian Channel while I was snorkeling along the cliffs of the island. It is a protected species due to the reduction of the population also due to the indiscriminate collection by divers and owners of marine aquariums: for its ease of breeding and adaptation.
Echinoderms possess a unique water vascular system. This is a network of fluid-filled canals derived from the coelom (body cavity) that function in gas exchange, feeding, sensory reception and locomotion. This system varies between different classes of echinoderm but typically opens to the exterior through a sieve-like madreporite on the aboral (upper) surface of the animal. The madreporite is linked to a slender duct, the stone canal, which extends to a ring canal that encircles the mouth or oesophagus.
From this, radial canals extend along the arms of asteroids and adjoin the test in the ambulacral areas of echinoids. Short lateral canals branch off the radial canals, each one ending in an ampulla. Part of the ampulla can protrude through a pore (or a pair of pores in sea urchins) to the exterior and is known as a podium or tube feet. The water vascular system assists with the distribution of nutrients throughout the animal’s body and is most obviously expressed in the tube feet which can be extended or contracted by the redistribution of fluid between the foot and the internal sac.