Phylum Echinodermata

Question 1

What are the key features of Echinodermata?

Answer 1

Bilateral larvae, pentaradial (5-ray symmetry) adults
No head/cephalisation
No osmoregulatory structures
Large 3-part coelom - all parts used in circulation
Amazing regenerative abilities
Most have simple gonads, separate sexes, free-spawning
Most lack a respiratory system
Complete digestive system, but anus may be secondarily lost

Question 2

What is the 3-part coelom comprised of?

Answer 2

Perivisceral coelom (open/hollow space in cavity)
Water vascular system - circulation, gas exchange (via tube feet), excretion, and locomotion.
Hemal system - circulation of nutrients from digestive system.

Question 3

What is the water vascular system and what is its role?

Answer 3

Derived from coelom - a closed system of canals and tube feet
Used for circulation + locomotion
Water enters through the madreporite and moves into the ciliated stone canal, then into the ring canal that branches off into radial canals that reach down into smaller tubes in the arms.

Question 4

How do echinoderms move?

Answer 4

Via tube feet, which use a hydrostatic mechanism to contract the ampulla filling the podium, and vice versa. By repeating this process of hydraulic locomotion, as one tube foot attaches and releases the next will follow in its place.

Question 5

Why do Echinoderms have spiny skin?

Answer 5

Due to ossicles that form the endoskeleton. They can fuse into skeletal plates and are formed in the dermis, covered by the epidermis, and bounded by connective tissue and muscle.