Echinoderms Characteristics

Echinoderms are marine animals which are typically characterized by their radial symmetry and water vascular system. These animals neither have a brain nor any complex sensing organ. So, how do they manage to carry out all life tasks which we do with the help of our brain and sensory organs? In order to understand that, you need to get a good understanding of some general characteristics of these marine animals.

Phylum Echinodermata

In marine biology, those marine animals which belong to phylum echinodermata are known as echinoderms. Interestingly, the name echinodermata is derived from a Greek word meaning 'spiny skin'. This phylum contains more than 6000 species of marine animals, which includes species of starfish, brittle stars, sea urchins, sea cucumbers etc. This phylum of marine animals is believed to be existing on the planet since the Cambrian period. They are found in all oceans of the world at different depths, with major concentration being observed near the coral reefs.

Characteristics of Echinoderms

With more than 6000 species making up the echinodermata phylum, it has to be quite diverse in nature and that's exactly the fact that their characteristics highlight. Basically echinoderm characteristics can be broadly categorized into two groups - general characteristics, i.e. the characteristic traits of all the species, and unique characteristics, i.e. the characteristics which are restricted to a few species in this phylum. Given below are the details of each of these groups.

General Characteristics
One of the characteristic trait on the basis of which you can identify these marine animals, is their radial symmetry. All the animals which belong to phylum echinodermata are typically characterized by a central structure surrounded by 5-part symmetry. This trait can be easily observed in starfish and brittle stars. Even though it is not so obvious in sea urchins and sea cucumbers, a closer examination of their anatomy shows that even they have a radical symmetry.

Yet another common trait observed in these species is their internal skeleton covered with spines and skin. This, however, tends to differ from one species to another. In sea cucumbers the skeleton is made of degenerated calcareous plates which are buried in the fleshy body, while the anatomy of the starfish reveals that its skeleton is made from movable calcareous plates thus forming flexible joints.

The third, but the most important characteristic traits of echinoderms is their water vascular system. It is most important because almost all the functions of these creatures, including locomotion, respiration and feeding, are facilitated by this process. The water vascular system is basically a hydraulic network of canals - which runs through the entire body of these marine animals. These animals carry out various life functions by varying the internal water pressure in this hydraulic network.

Unique Characteristics
While those were some of the most common characteristics, some of these creatures do demonstrate some unique characteristic traits. Even though most of the echinoderms are benthic in nature - i.e. they live on ocean floor, there do exist some species which have the tendency of floating (such as sea cucumbers) and swimming (sea lilies). Similarly, there also exist echinoderms who take help of some floating debris (crinoids) or fish (sea cucumbers) to move from one place to another. Though the 5-part symmetry is very common, some species starfish and crinoids exhibit a radial symmetry which is in multiples of five. For intance, the Helicoilaster - a type of starfish possesses up to 50 arms.

These sea creatures are important for the biodiversity of our planet, because very few species are able to survive in these parts of oceans which are deficient in terms of biotic factors. These marine animals also play a crucial role when it comes to geological environment of the planet as they contribute to various geological processes at the ocean floor - including limestone formation. As far as their relationship with humans is concerned, they are harmful as well as of great help. While some echinoderms like the sea urchins, have numerous spines which can pierce human skin and require medical intervention for removal, others such as the sea cucumbers are often considered delicacies in various parts of the world.