Echinodermata

Question 1

Features of the echinoderms

Answer 1

Deuterostomes
Radial and indeterminate cleavage
Coelom forms from out-pocketing of the mesoderm
Anus from blastopore
Groups exclusively marine and are separate sexes
Pentamerous radial symmetry
Hox genes expressed in order like bilaterally symmetrical animals
-more limbs appear with mutations to hox genes
Tube feet (podia)
Mutable connective tissue

Question 2

Symmetry in echinoderms

Answer 2

Show radial symmetry even though they are bilaterally symmetrical
Not related to other radially symmetrical groups
May have taken on this form as they are sessile and filter feeders (majority) - found in benthos so advantageous
Larvae bilaterally symmetrical - can disperse

Question 3

Variation in larval form

Answer 3

Larvae show convergent evolution with one another - between the less closely related groups
Some have lost the larval stage
Some increased yolk they develop from (eventually becoming so much = no larval)
Some brood their offspring
Converge to forms for maxing motility, SA and food intake = adapting in similar ways
Adult develops in larva (no transformation)

Question 4

Internal skeleton

Answer 4

Made of ossicles - CaCO3

• allows growth without moulting as is crystal skeleton structures separated by living tissue
• living tissues lightens it
• sea urchins ossicles have been fused = test
• can be tiny or absent = sea cucumbers

Question 5

Tube feet

Answer 5

Podia - oral side usually
-can be large and used in both locomotion and feeding
-some are small and used for respiration and suspension feeding
Crinoids - mouth on top of animal with tiny podia acting like cilia passing food to mouth

Question 6

Water-vascular system

Answer 6

Series of canals branched out through animal and full of fluid
-connection with sea water to manipulate podia
-opening to outside by madreporite
-radial canals down each leg - branches off were podia are
-ampulla are at same end but opposite side to podia
-ampulla muscle contracts and push fluid into podia so they stretch out, podia contract and push water back into ampulla
-valves allow water flow into ampulla and podia from radial canal
Sea urchins (only) have suction grip from this

Question 7

Mutable connective tissue

Answer 7

Changes tissues rigidity - stiff or flexible
Under nervous control
Changes in fluidity and flexibility of collagen fibres in tissue allow this
Can do very quickly - and not strenuous in energy demands
Sra urchins moving their spines for example
Sea cucumbers can become very floppy (protection)