Brittle Star By Ryan O'Meara

Habitat: the brittle star can be found 350 meters down from the surface of the ocean in hard sand or gravel from the subtidal zone. It lives in the deep sea.

Diet: It eats organic particles and other small animals like crustaceans. Different types of brittle stars eat in different ways: some eat food particles suspended in water, some eat organic particles that are on the seafloor, and some detect food by its odor.

Conservation status: They are currently on the endangered species list. In Port Phillip Bay, where some brittle stars are located, the beach is very urbanized and there is a lot of carbon emissions that are released from the nearby city that is affecting the muscle mass of the brittle stars. In acidic conditions like this, brittle stars need to regenerate their arms, which makes them lose muscle mass. This results in an alarming decreasing rate of brittle stars and their larvae.

Unique Characteristics: Their long whip-like arms can reach up to 60 cm in the biggest brittle stars. They can also regenerate lost arms or arm segments and use this to escape their predators. When they encounter a predator, some species can deliberately jettison their arms to elude their predator.

Predators: The glaucous-winged gull and the Puget Sound king crab. The gull swallows the entire star by bending the two stiff arms together and pushing them into its beak and then bends the remaining arms into the ground and then proceeds to swallow the whole specimen whole. Their main predators are the ballan wrasses, cuckoo wrasses, common dragonets, velvet crabs, spiny starfish and common starfish.

Reproduction: Brittle stars can reproduce asexually in two ways. The first way is when the arms and a portion of the central body break off and both pieces grow new bodies and arms to form another animal. The other way is when a brittle star is still young, and reproduce during their "settling stage". When their bodies are almost done being made, they lose two larval arms. At that point of attachment, special tissue is created which forms something called ophioplutei, and that swims off and creates new bodies of brittle stars.

Adaptations: In order for the brittle star to survive in its environment against its predators, it can readily remove its arms from its central body in order for it to run away from its predators. Some can also use the color of their bodies in order to blend into rock surfaces and sand.

Level of Organization: Brittle stars have a water vascular system, where the water is brought into the body using the madreporite, which is located on the underside of the body. It does not have a brain, but within the central disk are the stomach, genitals, muscles and a mouth surrounded 5 jaws. The arms of the brittle star are surrounded by vertebral ossicles (plates) made from calcium carbonate. These plates give the brittle star its flexibility in its arms. These plates are moved by mutable collagenous tissue, which is a type of connective tissue that is controlled by the nervous system. This allows the brittle star to be very flexible, move quickly and squeeze into tight spaces.

Significance: Brittle stars are prey to various types of fish, crabs and starfish. They can use their large beds for shelter for other animals such as bivalves. They remove particles from the water column by eating diatoms and phytoplankton, as well as decaying material off of the seafloor. They are host to many ectoparasitic copepod species as well as orthonectid species.

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