Introduction:

Echinoderms have been known since antiquity; echinoids, for example, were widely employed for medical and culinary purposes by the Greeks and Romans. During the Middle Ages, fossil echinoids and fragments of ancient crinoids were considered unlucky. Echinodermata was identified as a distinct group of animals in the early nineteenth century, and was occasionally combined with cnidarians and selected other phyla in a division of the animal kingdom known as the Radiata; the concept of a Radiata superphylum is no longer viable. Echinoderms are classified into 21 classes based primarily on skeletal structure distinctions. There are over 6,500 living species, and approximately 13,000 fossil species have been described.

General features:

Size range and diversity of structure :

Although most echinoderms are small, measuring up to 10 cm (four inches) in length or diameter, some can grow to be quite enormous; for example, some sea cucumbers can grow to be two metres (6.6 feet) long, and a few starfishes can grow to be one metre in diameter. Some of the largest echinoderms were extinct (fossil) crinoids (sea lilies) with stems as long as 20 metres (66 ft).

Role in nature :

Echinoderms are excellent scavengers of decaying debris on the seafloor, and they prey on a range of microscopic species, helping to keep their numbers in check. When in huge numbers, sea urchins can ruin tropical seagrass beds, harming the organisms that live there. Sea urchins that burrow into rocks and along shorelines can hasten shoreline erosion.

Relation to human life :

Some of the bigger tropical sea cucumber species, known commercially as trepang , are dried and eaten in soups, especially in Asia. Raw or fried adult sea urchin sex organs, or gonads, are considered a delicacy in several regions of the world, including Europe, the Mediterranean region, Japan, and Chile. Some tropical holothurians produce a toxin called holothurin, which is harmful to many species; Pacific islanders kill fish by poisoning water with holothurian body tissues that release the toxin. Holothurin does not appear to be harmful to humans; in fact, the toxin has been discovered to slow the growth of certain types of tumours, suggesting that it may have medical applications.

Characteristics of Echinodermata:

1. They are round or elongated and have a star-like appearance.

2 .They are only found in the sea.

3. The creatures have a spiky skin.
4. They are organised at the organ system level. Most members have both a circulatory and digestive system.
5. They have a coelomic cavity and are triploblastic.
6. Calcium carbonate is used to make the skeleton.
7. They have a free-flowing circulatory system.
8. They breathe by their gills or the cloacal respiratory tree.
9. They have a rudimentary radial nerve system, but no excretory system.
10. The body is not segmented, and there is no distinguishing head. The mouth is located on the ventral side, whilst the anus is located on the dorsal side.

Classification of Echinodermata:

1. Asteroidea

• They have a flattened, star-shaped body with five arms.
• Their tube feet have suckers on them.
• Papulae allow them to breathe.
• The body is made up of calcareous plates and movable spines.
• There is Pedicellaria present.
• For example, Asterias and Zoroaster

2. Ophiuroidea

• The body is flat and covered in pentamerous discs.
• There are no suckers on the tube feet.
•  Bursae allow them to breathe.
• The lengthy arms are separated from the central disc by a line.
• For example, Ophiderma and Amphuria.

       3. Echinoidea

• The body has a hemispherical shape.
• Suckers can be found in the tube foot.
• Arms do not exist on the body.
• The body is composed of a compact skeleton and moveable spines.
• For example, Echinus and Cidaris.

4. Holothuroidea

• The body is cylindrical and long.
• Arms, spines, and pedicellariae are all missing.
• They breathe via the cloacal respiratory tree.
• They have suckers on their tube feet.
• For example Holothuria, Cucumaria.

5. Crinoidea

• The body has a star form.

• There are no suckers on the tube feet.
• The arms are split in two.
• There are no spines or pedicellariae.
• For example, Neometra and Antedon.

Conclusion:  

From the following article we can conclude that Echinoderms have been known since antiquity; echinoids, for example, were widely employed for medical and culinary purposes by the Greeks and Romans. During the Middle Ages, fossil echinoids and fragments of ancient crinoids were considered unlucky.  They have a coelomic cavity and are triploblastic.Calcium carbonate is used to make the skeleton.They have a free-flowing circulatory system.They breathe by their gills or the cloacal respiratory tree.