1: The deuterostomes: Echinoderms

Question 1

Compare cleavage in the Proterostomes vs deuterostomes

Answer 1

Protostomes: sprial and determinate

Deuterostomes: Radial and indeterminate

Question 2

Name the phylums within Protostomes

Answer 2

Mollusk, annelida, nematoda, platyhelminthes and arthropoda

Question 3

Name the phylums within Deuterostomes

Answer 3

Echinoderms, chordates

Question 4

Compare coleom formation in protostomes vs deuterostomes

Answer 4

Protostomes: Solid mass of mesoderm splits to form coleom

Deuterostomes: Folds of archenteron form coelom

Question 5

Compare the fate of the blastopore in protostomes vs deuterostomes

Answer 5

Protostomes: Mouth forms first from the blastopore, anus 2nd

Deuterostomes: Anus forms first from the blastopore, mouth 2nd

Question 6

What are the characteristics of the echinoderms?

Answer 6

• 3 body layers
• Pentamerous radial symmetry (body divided into 5 parts)

(Not related to any other radially symmetrical groups
= Probably adopted radial symmetry to do with feeding)

Question 7

Describe the complex developmental transformation that Echinoderms undergo

Answer 7

Bilateral to radial:
- Adult arises from cells set aside in larva (maximal indirect development)
- Anterior-posterior body axis shifts, body twists around new axis
- Coelomic cavities undergo reorganisation

Question 8

Describe the internal skeleton of Echinoderms

Answer 8

• Each calcareous ossicle is separated by living tissue
  → allows increase in size without moulting
• Can be fused & hinged e.g urchins
• May be absent or minute e.g sea cucmbers

Question 9

Describe the tube feet of Echinoderms

Answer 9

Podia
-Large → used for locomotion & feeding
Small → used for respiration & suspension feeding (e.g in feather star and sea lily)

E.g Sea cucumber modified podia at end → for feeding

Question 10

Describe the Water-vascular system in Echinoderms

Answer 10

• Hydraulic system that controls the podia
• Canals around the body, connected to the outside by madreporite
• Contraction in ampulla causes podia to extend
• Contraction/ relaxation allows water to move to podia
• Podia can grip onto surfaces by:
• Starfish = chemical reaction on surface
• Urchin = suction cup

Question 11

Describe the mutable connective tissue in Echinoderms

Answer 11

• Rapid, reversible change in stiffness
• Under nervous control
• Due to change in viscosity of collagen fibres
• Doesn’t take much energy to
  Function: protection & movement

Question 12

Give some examples of how Echinoderms use their mutable connective tissue

Answer 12

Sea cucumbers:
Can release their guts as a defence mechanism

Sea urchin:
Can change spine stiffness

Question 13

Describe the nervous system of echinoderms

Answer 13

→ nerve net (no central brain)
But not so simple:
e.g In starfish locomotion the leading arm assumes a temporary brain function