We explain what starfish are, what their habitat and diet are like, and what their characteristics and reproduction are.
What are starfish?
It is popularly known as starfish. a class (Asteroidea) of underwater living beings and invertebratesbelonging to the phylum of echinoderms (such as sea urchins), whose bodies are made up of five or more long arms attached to a central disk, thus giving them the appearance of a star.
They have been identified up to 1600 different species in this same class of animalsdistributed throughout the world at different levels of ocean depth.
It is one of the most common and well-known inhabitants of the sea floor, which usually appear in various sizes and colors.
In most human cultures They are considered attractive beingsharmless, which are a symbol of marine life and coastal areas.
Many species of starfish are found at risk of extinction due to habitat destructionas a consequence of human activities in the oceans.
See also: Turtle
Origin of starfish
The presence of starfish in the fossil record, as well as other similar invertebrates, is not always easy to identify, given that its soft parts do not fossilize well and its most 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 It was between the Early Jurassic and the Middle Jurassicafter the mass extinction events during the Late Devonian and Late Permian, in which most species disappeared.
Where do starfish live?
starfish They inhabit ocean floors throughout the worldand are unable to survive in fresh water. The greatest variety of species is found in the tropical region of the Indo-Pacific Ocean, and the five-armed species are the most predominant of all.
You can see them up to depths of 6 kilometers below the surface.
What do starfish feed on?
It is generally about predators with non-specific habitscapable of eating mollusks, clams, oysters, snails or any animal unable to evade their slow attack.
Many They feed on detritus or decaying mattersuch as dead or almost dead animals, sponges, plankton, or organic sheets attached to substrates.
Some species like Acanthaster planci It feeds on coral polypsthus constituting a potential threat to the regrowth of weakened coral reefs.
Parts of the starfish
The body of starfish is made up of two parts: a central disk, endowed with radial symmetry, where its organs and mouth are; and a set of hollow limbs, which can range in number between 5 and 40.
Both parties meet covered with a rigid crustmore resistant, made of calcium carbonate sheets, called ossicles, in which spines or granules can be found on the outside.
Under, They have tube feetwhich are small appendages that perform locomotion and chemical transport functions.
The very body of the starfish It is made up of various layers of tissuewith a thin epidermis and a thicker dermis, between which the circulatory system occurs.
At the end of each limb, there is also an ocellus (simple eye) that allows the detection of movement and variations between the presence and absence of light.
These animals They lack a centralized brain and few sensory inputs, but even then they are sensitive to light, touch, temperature, orientation, and surrounding waters.
Reproduction of starfish
Starfish can reproduce in two ways:
- In a sexual way. Most starfish species present a clear distinction between males and females, although this difference is not externally perceptible. Others, too, are simultaneous hermaphrodites (they have both sexes) or secondary hermaphrodites (they can alternate). In any case, reproduction in this case occurs through the release of gametes from the ducts located between the arms, in the center of the organism. In most cases this involves external fertilization, in which sperm and eggs are in the water (free spawning), developing eggs attached to stones and other surfaces.
- Asexually. Many times starfish reproduce autonomously, by fission of their central discs or amputation of their arms, from which the entire individual can reproduce. This is even possible to observe among larvae of these animals, and even by budding.
How do starfish move?
starfish they move slowly and imperceptiblythanks to the set of appendages (feet) that cover the lower part of their bodies.
This works through an internal water circulation system and the secretion of chemicals that transform the end of the foot into a kind of suction cup.
That’s why the stars can adhere strongly to rocks or to the surface of ships, even defying gravity in doing so.
How long do starfish live?
The lifespan of a starfish depends on the species. The largest ones usually live longer than the smallest onesbeing able to live up to 10 years (and reach sexual maturity at 2) or even reach 34 years of age.
How do starfish breathe?
These animals They breathe through their tube feetthrough which the entry of oxygen from the water is allowed through the internal fluids of the body cavities.
Between one layer of fabric and the other, oxygen enters the animal. Therefore, they cannot breathe outside of water and the lack of humidity in the air dries them out quickly.
Tissue regeneration
Many species of starfish They are capable of regenerating their lost tissuesfor example, of its limbs. And depending on how much of the central disk survives, it is possible that such regeneration could involve large portions of the entire organism.
State of conservation
Although These are extremely abundant animals and not being particularly threatened with extinction, they are at the same time especially sensitive to the presence of toxins or chemicals in the water as it is pumped in and out of their bodies.
For that reason, Oil or chemical spills are terrible for themas are, although it may not seem like it, the brief moments in which tourists usually take them out of the water to photograph them or see them up close, preventing them from carrying out their gas exchange, that is, drowning them.