Starfish have always amazed naturalists and amateurs. It is normal to be fascinated by the beauty of its symmetry and its colors, as well as its strange way of life. These curious animals are distributed throughout the seas around the world, and can be found in the most remote places. There, they live sedentary, hidden, waiting for the opportunity to find prey.
Apparently harmless, starfish hide a terrifying mouth on the underside of their bodies. It is used to scrape hard substrates or catch their prey, since most of them are carnivorous. However, they do not breathe through their mouths. So how do starfishbreathe? We tell you about it in this article on our site, where we do a little review of its anatomy.
What are starfish?
To understand how starfish breathe we must first ask ourselves what they are. These curious animals are part of the phylum of the echinoderms (Echinodermata). They are closely related to other very enigmatic animals: brittle stars, lilies, daisies, cucumbers and sea urchins. All of them have radial symmetry and have their body divided into five equal parts. They also have a very characteristic calcareous skeleton.
Within the echinoderms, starfish form the class of asteroids (Asteroidea). They are about 2,000 species that have many things in common, such as their peculiar star shape, their slow movement and their anatomy. However, it is a very large and diverse group. Some species measure just a few millimeters, but others can reach a meter in diameter. Most are voracious predators, although others are omnivores, herbivores or even filter feeders.
If you want to know more about the diet of these curious animals, don't miss this other article on "What do starfish eat".
Anatomy of Starfish
Starfish are made up of a central disk divided into five equal parts From each of them, an arm or spoke comes out finished in a point, giving it its characteristic star shape. However, some species have more than five arms, such as the impressive sun star (Heliaster helianthus). They are normally covered by a bony skeleton, made up of small pieces or ossicles that lie just under the skin.
In this way, its body is flattened and has radial symmetry. On its bottom or oral is the mouth, right in the middle. Therefore, to eat they are placed on top of their prey or food. From its mouth depart the ambulacral areas that go towards the tip of each arm. Each of them is covered by rows of tube feet These are part of the internal tube feet, a hydraulic structure that helps them move.
On the upper or aboral part of the starfish we find the anus, also in the center. Next to it stands out the madreporite, a series of pores that communicate with the ambulacral apparatus. Normally, the aboral face is covered with bony spines, which may or may not be flattened. At its base, some pedicelaria or shells appear that help clean the surface of the body and protect soft structures that protrude between the ossicles: the dermal papules or gillsThese are the key to understanding how starfish breathe.
Finally, in the area surrounding the anus there are also gonopores, small holes that are used to release their gametes during sexual reproduction. You want to know more? Then don't miss this other article on "How Starfish Reproduce".
Where do starfish breathe?
We already know these members of the animal kingdom well, so we're ready to find out how starfish breathe. Inside, echinoderms house a space filled with fluid known as coelom Their walls They are covered by cilia or hairs that move the liquid throughout the body, bathing the internal organs. It communicates with the outside thanks to some soft bumps that appear on the surface of the body: the papules.
The wall of the papules is very thin and gas exchange takes place there. Oxygen (O2), more abundant in seawater, enters the interior of the animal's body by diffusion. Carbon dioxide (CO2), which is more abundant inside the star, flows by diffusion into the seawater along with other waste, such as ammonia (NH3). Thus, gases and small substances move from where they are more abundant to where they are less.
Therefore, the coelom not only functions as your respiratory system, but also as your excretory system. The fluid in the coelom collects waste produced by the internal organs, such as CO2. In turn, it provides them with oxygen and small nutrients that enter the papules by diffusion. This is how starfish breathe and also how they clean themselves.
Furthermore, these invertebrate animals can breathe through their aquifer system or ambulacral, an internal cavity that only appears in echinoderms. It is a system of channels or hydraulic device that ends in the tube feet, projections that fill and empty with water. They function as a kind of suction cups, allowing the movement of the animal. In a very small quantity, O2 can enter and CO2 exit through them.
