Tuesday, October 12, 2021

Starfish (Sea stars)

Sea stars are all members of the phylum Echinodermata and the class Asteroidea. The starfish have been known from the earliest times, and the Greeks applied to them the name Aster, meaning star.

Around 1,500 living species of starfish occur on the seabed in all the world's oceans, from the tropics to subzero polar waters.

Sea star habitats are highly variable; these animals can be found in all ocean basins of the world and at a large assortment of depths and bottom composition. They are benthic animals, which means that they live on the ocean floor whether they are in deep or shallow water.

The underside of Sea stars are covered with hundreds of tiny feet. These are called tube feet. They use their tube feet to slowly crawl along the floor because starfish cannot swim.

The body wall consists of a thin cuticle, an epidermis consisting of a single layer of cells, a thick dermis formed of connective tissue and a thin coelomic myoepithelial layer, which provides the longitudinal and circular musculature.

The dermis contains an endoskeleton of calcium carbonate components known as ossicles. These are honeycombed structures composed of calcite microcrystals arranged in a lattice.

Starfish are really good at keeping themselves safe. They have thick skin and it is very prickly. This makes them hard to eat. Some starfish can change colour so that they match what they are sitting on. This makes them hard to see.

Sea stars can live a relatively long time. Some species, including the sunflower sea star, Pycnopodia helianthoides, live for more than 30 years.
Starfish (Sea stars)

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