Invertebrates Facts

  • Invertebrates are multi-cellular and all the cells have different responsibilities to keep the animal alive.
  • Invertebrates have no backbone or bony skeleton or cells wall like all other animals.
  • Invertebrates like echinoderms do not have heads.
  • There are millions of invertebrates living in our house in the name of dust mites which are hardly visible to human eyes.
  • Invertebrates under a process called metamorphosis through which they change form as they grow.



Echinoderms are species that belong to the phylum Echinodermata. The phylum contains about 6000 species. Echinoderms get its name from the Greek word which means "Spiny Skin," But not all the Echinoderms have spiny skin. This group of species is found literally in the sea and cannot be seen anywhere in the land.

The most common characteristic that is common in all the echinoderms are they are radically symmetrical which means that these species have appendages that point outwards from the centre of the body. Generally these appendages are five in number. The larvae of the Echinoderms are bilaterally symmetrical as they reach their adulthood they become radically symmetrical. Most of the Echinoderms have suckers at the end of the feet which they use to capture and hold the prey.

Learn more about the characteristic of the Echinoderms from the page Characteristic of Echinoderms.

Echinoderms are also called as Echinodermata and spiny skinned animals.

Echinoderms are entirely marine species. They are mostly seen in the inter-tidal zones deep in the ocean and they are also found in the cold and tropical seas.

Echinoderms have several unique features that are not found in any other animals. The body wall has a limestone skeletal system called as Stereom. The echinoderms have a special ligament that helps them to stiffen or loosen their body without spending much energy. The males and females echinoderms are separate. Echinoderms have tube feet which helps them in many purposes. To learn more about the body structure of the echinoderms move to the page Anatomy of Echinoderms.

Behavior of Echinoderms

Some species of the Echinoderms like starfish are carnivorous, others like sea cucumbers are detritus foragers, and some like basket stars are plankton feeders. Echinoderms have the ability to regenerate their missing organs.

Reproduction takes place by releasing the sperms and eggs into the water. Most of the species produce free floating plantonic larvae which feed on the plankton. The larvae are bilaterally symmetrical and when they reach the adulthood they become radically symmetrical. Some species of Echinoderms reproduce by asexually that is they break their ray or arm or split themselves into half. Thus each part becomes a new animal.

The body of the Echinoderms is protected by the spiny skins and spines. Though they are protected by spiny skins still they are hunted by some fish, crabs, shrimps, and other Echinoderms which are carnivores. Some echinoderms are nocturnal that is they expose themselves at night time only.

Echinoderms are classified into the following five groups. They are Asteroidea (starfish, sea stars), Ophiuroidea (brittle stars), Echinoidea (Sea Urchins), Crinoidea (Feather Stars), and Holothuroidea (Sea Cucumbers). To know briefly about the each classification move on to the page Classification of Echinoderms.

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