Deuterostomes

Question 1

What are characteristics of deuterostomes?

Answer 1

Triploblasts.
True coelomate. 
Blastopore becomes anus.
Coelom develops from mesodermal pockets that bud from gastrula cavity.
Radial and indeterminate cleavage.

Question 2

What are the three main clades of deuterostomes?

Answer 2

• Echinoderms - sea stars and urchins.
• Hemichordata - acorn worms and pterbranchs.
• Chordata - sea squirts, lancelets and vertebrates.

Question 3

Give characteristics of the Xenoturbellids.

Answer 3

• Small wormlike animals that feed on molluscs.

- Simple body plan, no well-defined organ systems.

Question 4

Give characteristics of Acoels.

Answer 4

• Simple, wormlike animals.

- No gut, circulatory, respiratory, excretory or body cavity.

Question 5

Give characteristics of Echinodermata.

Answer 5

• No head, move in all directions.
• Oral side has mouth, aboral side has anus.
• Bilaterally symmetrical as larvae, radially symmetrical as adults.
• External fertilisation, sexual reproduction.
• Dioecious.
• Can replicate by parthenogenesis.
• Endoskeleton under epidermis composed of small calcareous plates called ossicles.

Question 6

Describe an echinoderms water vascular system.

Answer 6

• A network of water-filled canals leading to extensions called tube feet.
• Hydraulic system used for locomotion, gas exchange and feeding.
• Tube feet lack circular muscles.
• Fluid pumped into foot by ampulla contraction.
• One-way valve at junction of ampulla/radial canal.
• Tube foot retracts when longitudinal muscles in tube foot contract.

Question 7

Give characteristics of the Asteroidea.

Answer 7

• Sea stars.
• Regenerative.
• Predatorial.
• Gonads and digestive system in arms.
• Macrophagous feeding.
• e.g. Crown of Thorns (largest sea star).

Question 8

Give characteristics of Echinoidea.

Answer 8

• Sea urchins.
• Spherical.
• Lack arms, appendages are spines called pedicellaria.
• Catch plankton with tube feet and scrape algae with a rasping structure.
• e.g. Aristotle’s lantern.

Question 9

Give characteristics of Crinoidea.

Answer 9

• Sea lilies.
• Attach to substrate by stalk.
• Feather star, grasp substratum with flexible appendages, limited movement.
• Side branches = pinnules.

Question 10

Give characteristics of Ophiuroidea.

Answer 10

• Brittle stars and basket stars.
• Brittle stars ingest sediment and digest the organic material.
• Basket stars are mucociliary suspension feeders.
• Large stomach, no intestine or anus.
• Long slender arms made of jointed plates.

Question 11

Give characteristics of Holothuroidea.

Answer 11

• Sea cucumbers.
• Soft bodies with reduced ossicles.
• No arms, bilaterally symmetrical.
• Tube feet modified into feathery sticky tentacles from mouth.
• Some expel cuverian tubules (toxic structures).
• Some eviscerate (expel digestive system).