Echinoderms

Question 1

What are the five extant classes of Echinoderm?

Answer 1

Ophiuroid (Brittle Star)
Asteroid (Sea Star)
Crinoid (Sea Lilly)
Echinoid (Sea urchin)
Holothurian (Sea Cucumber)

Question 2

Who are Echinoderms most closely related to? Why?

Answer 2

Chordata and Hemichordates because they too are deuterostomes.

Question 3

What symmetry do most echinoderms have?

Answer 3

-Pentaradial (5 arms)
- Secondary bilateral
- Meaning pentaradial but during development they are bilateral
- Extinct echinoderms have many symmetries (bilateral, none, etc)

Question 4

What is the echinoderm skeleton comprised of?

Answer 4

CaCO3.
- Mesodermal skeleton of plates covered by epidermis
- High magnesium calcite levels
- Porous structure called stereom filled with stroma (cells and fibres)

Question 5

Describe the characteristics and functions of the water vascular system.

Answer 5

• Fluid filled canals around the body, with a central ring connecting to all arms and controlling tube feet.
• Used for locomotion, feeding, respiration
• Extended/retracted by hydraulic pressure
• Opens via the hydropore

Question 6

Describe the echinoderm nervous system.

Answer 6

• Decentralised
• Radial nerves down all ambulacra (grooves) connected by a nerve ring.
• Located primarily within ectoderm of tube feet

Question 7

Name the phases of echinoderm life cycles.

Answer 7

Embryo to pluteus (looks like a robot) to settler to juvenile to adult that releases gametes.

Question 8

What are the two subphyla of echinoderms?

Answer 8

Pelmatozoa (Crinoids)
Eleutherozoa (Everything else)

Question 9

Give a summary of Crinoids.

Answer 9

• Passive suspension feeders
• Stalked, attached to substrate. Stalks made of calcite ossicles called columnals.

Question 10

Give a summary of Ophiuroids.

Answer 10

• Five long, flexible arms used for locomotion and distinct disk that contains all viscera.
• Scavengers, detritus feeders, filter feeders.
• Some have highly branched arms.
• Arms supported by internal skeleton plates.

Question 11

Give a summary of the Echinoids.

Answer 11

• Covered in movable spines
• Some pentaradial, some secondary bilateral

Question 12

Describe Echinoid skeletons.

Answer 12

• Skeleton made of interlocking plates
• Ambulacral areas associated with tube feet. interambulacral areas bear large spines.

Question 13

What is the Aristotle’s lantern?

Answer 13

• Five pyramids in interambulacral space
• Each made of two hemi pyramids supporting a long growing tooth.

Question 14

Give a summary of the irregular echinoids.

Answer 14

• Sand dollars
• Secondary plane of bilateral symmetry
• Anus has migrated so axis is front/back.
• Many have lost Aristotle’s lantern.

Question 15

Give a summary of holothurians.

Answer 15

• Most derived echinoderms
• Soft bodied with reduced skeleton, that just comprises of wheel shaped ossicles.