Characteristics of Echinodermata: Study Notes

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General Characteristics of Echinodermata: The Spiny-Skinned Animals

The phylum Echinodermata encompasses a unique group of marine animals characterized by their spiny skin and pentaradial symmetry. Here are the essential features that define echinoderms:

1. Name Meaning

• The term Echinodermata is derived from Greek words: “echino” meaning spines and “derm” meaning skin, referring to the spiny surface common to most members of this phylum.

2. Phylum Size

• Echinodermata is the second smallest phylum in the animal kingdom, containing approximately 6,000 species.

3. Habitat

• Echinoderms are exclusively marine animals, living in various oceanic environments, from shallow waters to deep-sea habitats.

4. Body Spines

• Members of this phylum often have small or long spines on their body surface, giving them the characteristic spiny appearance that defines their name.

5. Body Organization

• Echinoderms are multicellular, triploblastic animals with pentaradial symmetry, a characteristic feature in adults. They are also coelomate (having a true body cavity) and deuterostomes (where the anus forms before the mouth during development).

6. Symmetry

• Echinodermata is the only phylum that displays two symmetries throughout its life cycle. The larvae exhibit bilateral symmetry, while adults show pentaradial symmetry.

7. Skeleton

• Echinoderms possess an endoskeleton made up of hard calcareous plates that are covered by a thin epidermis. This skeletal structure provides both support and protection.

8. Body Structure

• Echinoderms have an unsegmented body and lack both a head and a centralized brain, relying instead on a nerve ring and radial nerves.

9. Water Vascular System

• Unique to echinoderms, the water vascular system is an intricate network involved in nutrition, respiration, excretion, and locomotion. This system transports water through canals, enabling movement and feeding.

10. Tube Feet

• Echinoderms are equipped with muscular tube feet, which aid in locomotion, holding food, and respiration. These tube feet function through hydraulic pressure, controlled by the water vascular system.

11. Nervous System

• The nervous system of echinoderms is poorly developed, consisting of a nerve ring with radial extensions. They also have limited sensory organs.

12. Larval Stage

• The developmental stage includes a Bipinnaria larva, which exhibits bilateral symmetry before metamorphosing into the radially symmetrical adult.

13. Regeneration

• Echinoderms have a significant ability to regenerate lost body parts, such as arms and spines, making them one of the most regenerative groups among animals.

14. Evolutionary Link

• Echinoderms are thought to have evolutionary ties with chordates and hemichordates, sharing a common ancestor known as the dipleura.

15. Examples

• Notable examples of echinoderms include starfish, brittle stars, sand dollars, sea cucumbers, sea urchins, and sea lilies.

Echinodermata stands out due to its unique water vascular system, spiny endoskeleton, and diverse body forms. Exclusively marine, echinoderms play essential ecological roles and are evolutionary relatives to chordates, contributing to our understanding of vertebrate ancestry.

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