Echinoderms

Question 1

Question: What are echinoderms?

Answer 1

Answer: Echinoderms are marine animals with a spiny skin. They first appeared in the seas around 400 million years ago.

Question 2

Question: What are the key characteristics of echinoderms?

Answer 2

Calcareous endoskeleton covered by an epidermis
Adults with radial symmetry, larvae with bilateral symmetry
Dermal branchiae (tuft gills) for gas exchange
Complete digestive tract with separate mouth and anus
Nervous system consisting of nerve net, nerve ring, and radial nerves
Water-vascular system for locomotion, attachment, and feeding

Question 3

Question: What are the five classes of echinoderms?

Answer 3

Asteroidea (sea stars)
Echinoidea (sea urchins, sand dollars)
Holothuroidea (sea cucumbers)
Ophiuroidea (brittle stars, basket stars)
Crinoidea (sea lilies, feather stars)

Question 4

Question: How do sea stars feed?

Answer 4

Answer: Sea stars feed by everting their stomach and externally digesting their prey. They are predators or scavengers and commonly feed on snails, bivalves, crustaceans, polychaetes, corals, and more.

Question 5

Question: What is the unique feeding apparatus of sea urchins?

Answer 5

Answer: Sea urchins have a specialized feeding apparatus called Aristotle’s lantern. It is made up of five protractable calcareous plates that scrape food off the substrate, tear food chunks, and masticate food particles.

Question 6

Question: How do brittle stars and basket stars differ in feeding behavior?

Answer 6

Answer: Brittle stars are predators or scavengers, while basket stars are suspension feeders that trap plankton with their mucus-covered tube feet.

Question 7

Question: What is the notable symbiotic relationship involving sea cucumbers?

Answer 7

Answer: Sea cucumbers have a symbiotic relationship with pearl fish. Pearl fish live inside the intestine/anus of sea cucumbers, benefiting from protection, while the sea cucumber is neither harmed nor benefited (commensal symbiosis).

Question 8

Question: What is the unique feature of crinoids (sea lilies, feather stars) compared to other echinoderms?

Answer 8

Answer: Crinoids use their arms and tube feet for suspension feeding. They have a nervous system, a short U-shaped intestine, and cirri under the oral disk for attachment to substrates or living on soft sediment.