Although commonly known as starfish, these animals are not fish but echinoderms, animals that are closely related to sea urchins.
DIARIO DEL HUILA, ENVIRONMENT
A class (Asteroidea) of underwater living beings and invertebrates, belonging to the phylum of echinoderms (such as sea urchins), whose bodies are formed by five or more long arms attached to a central disc, are popularly known as starfish. thus giving them the appearance of a star.
Up to 1,600 different species have been identified in this same class of animals, distributed throughout the world at different levels of ocean depth.
They are one of the most common and well-known inhabitants of the sea floor, often appearing in various sizes and colors.
appendages.
In most human cultures they are considered attractive, harmless beings, which are a symbol of marine life and coastal areas. Many species of starfish are at risk of extinction due to the destruction of their habitat as a consequence of human activities in the oceans.
Origin of starfish
The presence of starfish in the fossil record, as well as other similar invertebrates, is not always easy to identify, since their soft parts do not fossilize well and their more rigid parts separate from the rest when the animal decomposes. However, it is estimated that its evolutionary origin would be in the Ordovician period, in the Paleozoic Era, approximately 485 million years ago.
Its greatest stage of diversification as a species was between the Early Jurassic and the Middle Jurassic, after the mass extinction events during the Late Devonian and the Late Permian, in which most species disappeared.
Where do sea stars live?
Starfish inhabit ocean floors throughout the world, and are incapable of subsisting in fresh water. The greatest variety of species is found in the tropical region of the Indo-Pacific Ocean, and the five-armed are the most predominant of all. They can be observed to depths of 6 kilometers below the surface.
What do starfish eat?
They are generally predators with little specific habits, capable of eating molluscs, clams, oysters, snails or any animal unable to evade their slow attack. Many feed on detritus or decaying matter, such as dead or nearly dead animals, sponges, plankton, or organic sheets attached to substrates.
Some species, such as Acanthaster planci, feed on coral polyps, thus posing a potential threat to the regrowth of weakened coral reefs.
Parts of the starfish
The body of the starfish is made up of two parts: a central disk, endowed with radial symmetry, where its organs and its mouth are; and a set of hollow limbs, which can range in number from 5 to 40.
Both parts are covered with a rigid crust, more resistant, with sheets of calcium carbonate, called ossicles, in which thorns or granules can be found on the outside. Below, they have tube feet, which are small appendages that perform locomotion and chemical transport functions.
The body of the starfish itself is made up of various layers of tissue, with a thin epidermis and a thicker dermis, between which lies the circulatory system. At the end of each limb, there is also an ocellus (simple eye) that makes it possible to detect movement and variations between the presence and absence of light.