The Echinoderms

The echinoderms (from Greek echinos: thorns; derma: are a group of exclusively marine animals with an endoskeleton (endo = inside) limestone often provided with protruding spines, which justify the group's zoo name.

Although not a spine, it is important in supporting the body as it is well developed and sturdy. Among the echinoderms are starfish, sea cucumbers, sea lilies and sea urchins, among others.

The size of the echinoderms varies greatly; The starfish's diameter, for example, measured from end to end of its arms, can be from a few centimeters to a meter, depending on the species.


Echinoderm Characteristics

One of the most striking features of the echinoderms is the presence of a complex system of blades, channels and valves, called the aquifer or ambulatory (from Latin ambular: walk). This system relates to locomotion, breathing, circulation, excretion and even the perception of the animal.

The ambulatory feet have muscle walls and ampoules that accumulate fluid; Variations in the fluid pressure in the system determine the expansion or retraction of the feet, a fact that culminates with the displacement of the animal. When the pressure of the liquid is higher in the feet, the feet become stiffer, when the pressure decreases, they become soft - this difference allows movement.


The echinoderms feed on small animals and algae. The starfish, for example, is carnivorous. The vital systems of these animals are simple and efficient. The digestive system contains only mouth, stomach, intestines and anus. But the stomach is only present in the body of the carnivorous echinoderms, having glands that produce digestive substances.

Starfish feed mainly on small mollusks such as shellfish. With its small feet, the starfish forces open the oyster shells, then turns its own stomach inside out and throws a digestive juice into the shells. Then just swallow the mass, that is, the body of the already digested clam. This is therefore an extracorporeal digestion.

Sea urchin

The sea urchin feeds on the seaweed - it has the mouthpiece with "teeth" made of rigid substances. With these "teeth", he scrapes the algae stuck in the rocks. This hedgehog mouthpiece is named after aristotle lantern.


Elimination of excreta is facilitated by ambulatory system, by which water circulates in the body of the echinoderms.


Breathing - that is, gas exchange - is performed by tiny gills, near the mouth, and also along the length of the ambulatory feet, through which the water circulates.


There is a colorless liquid that circulates through the channels, located throughout the body of these animals. This fluid accomplishes a task similar to that of blood in our body, namely transporting substances throughout the body.

Sea lily



Echinoderms perform sexual reproduction, that is, reproduction with the participation of gametes. They have separate sexes and external fertilization occurs in water. Its development is indirect, because the larvae become young animals with their own form.


When the tail of a gecko is cut, in a few days a new tail grows, regenerating itself. This also happens when a starfish loses one arm.

This phenomenon of body part regeneration is an advantage for these animals, who, when attacked or in imminent danger, "deliver" part of their body to the predator while seeking to hide.

If the central disc is intact, there are starfish species that can move around and feed on only one arm while the process of regeneration occurs through cell division. The sea cucumber, in extreme danger, leaves part of its viscera (internal organs). This is advantageous as it distracts predators and gives you time to escape.

Sea cucumber