Seven-armed Starfish, Luidia ciliaris

The seven-armed starfish (Luidia ciliaris) is a species that can be found in the eastern waters of the Mediterranean Sea and the Atlantic Ocean. Its range extends from the Faroe Islands and Norway to the Azores and Cape Verde in the south. It is typically found on soft seabeds, although it may reside on rocks, at depths of up to 1,312 feet.

The seven-armed starfish is named for its seven arms, which extend from its disc-like body. It can reach an average body length of 1.3 feet from one arm to another. The body and arms are typically orange-brown in color, with whitish fringe occurring along the edges of each arm. Its skin is covered with many pillar-like spines known as paxillae. This species has no protective plates along the top side of its body, but its underside holds pedicellariae and a number of tube feet, which help it move around, although these feet do not create suction. Its reproductive organs are located along two arms, while its mouth can be found in the center of its body. This species has no anus, pyloric stomach, or intestines.

The breeding season for the seven-armed starfish occurs in the early summer months. Females first release millions of eggs into the water column, which encourages males to release their sperm shortly after. Fertilization occurs within four days, after which the zygotes turn into larvae that intermix with the plankton in the water column. After three to four months, the larvae are large enough to float to the sea floor, at which time seven arms can be seen developing. This species undergoes metamorphosis when it falls to the sea floor, a trait that is unique to the species.

The diet of the seven-armed starfish consists mainly of other species of echinoderms, although it will scavenge for food occasionally instead of eating live animals. Main prey items in the Irish Sea include Ophiura albida, a sea urchin known as Psammechinus miliaris, brittle stars, and Ophiothrix fragilis. Although it was found to consume Ophiocomina nigra in considerable quantities, this species was not a main prey item because it is more capable of escape than other species.

The seven-armed starfish is able to “walk” by lifting itself off the seabed and launching itself forward. It will do this when catching prey and will then consume its food by extending the plates around its mouth. The plates extend so far, that it can consume species that are larger than its mouth. After digesting what it can, this species will spit out the remains of its food.

Image Caption: Luidia ciliaris in Sala Maremagnum of Aquarium Finisterrae (House of the Fishes), in Corunna, Galicia, Spain. Credit: Cwmhiraeth/Wikipedia (CC BY-SA 3.0)

Seven-armed Starfish Luidia ciliaris

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