Lecture 13 - Echinoderms

Question 1

what 3 things define a deuterostome

Answer 1

• radial and indeterminate cleavage
• folds of archenteron form coelom
• anus develops from blastopore

Question 2

echinoderms have pentamerous radial symmetry - describe

Answer 2

body divided into 5 parts - not related to other radially symmetrical groups

Question 3

describe the larvae of echinoderms

Answer 3

larvae = bilaterally symmetrical - this is a useful feature of sessile animals to distribute their larva
- larvae show convergent evolution

Question 4

what is unusual about echinoderms which occurs despite their radial symmetry?

Answer 4

they have hox genes which they express in a particular order

- homeotic mutations can cause more limbs

Question 5

echinoderm internal skeleton and how it is advantageous

Answer 5

• made from ossicles made of calcium carbonate
• each ossicle has crystal structure separated by living tissue - means they can increase in size without moulting and lightens the structure of the skeleton

Question 6

what is a unique feature of echinoderms and another way it can be used

Answer 6

ossicles - can be fixed and hinged forming a casing around animals e.g sea urchins - can be absent/ tiny e.g. sea cucumbers

Question 7

what does echinoderm mean?

Answer 7

spiny skin

Question 8

podia

Answer 8

• tube feet
• large podia = locomotion + feeding
• small podia = respiration + suspension feeding

Question 9

water vascular system

Answer 9

• series of branching canals which operate the podia
• connect with sea water
• podium/ampulla branch off radial canals in each limb
• to move podia they close valve and push fluid into podia (contract pushes water into ampulla)

Question 10

how do sea urchins and star fish grip

Answer 10

sea urchin = suction cap at end of podium

star fish = chemical reaction - can feel different substances and move differently on them

Question 11

mutable connective tissue

Answer 11

they have the ability to go really floppy and large or really stiff and inflexible

• to do with collagen fibres fluidity in connective tissue
• could be used for protection

Question 12

what is a weird way echinoderms can protect themselves

Answer 12

can release their internal organs out of body to satisfy predator and then regenerate them

Question 13

5 echinoderm groups (exclusively marine)

Answer 13

• asteroidea (starfish)
• ophiuroidea (brittle stars)
• Echinoidea ( sea urchins)
• holothuroidea (sea cucumbers)
• crinoidea (sea lillies + feather stars)

Question 14

where is the mouth found in star fish?

Answer 14

mouth on underside and anus on top

Question 15

what is the ambulacral ridge in star fish

Answer 15

on the middle of the legs where the podia are found

Question 16

what are the pedicellaria in star fish?

Answer 16

pincers that remove any waste on the body

Question 17

what is the papula in star fish?

Answer 17

skin gills- projection of coleom which serves in gas exchange and excretion

Question 18

how do starfish feed

Answer 18

small armed tend to be scavengers and long arms are more predators
- can evert stomach inside a muscle shell digest and suck it back up

Question 19

star fish nervous system

Answer 19

• nerve net because of radial symmetry - but its more sophisticated because they can locally control parts of the net
• leading arm functions temporarily as a brain telling body to walk in direction of leading arm
• control comes from radial nerves send message through nerve ring

Question 20

why can the starfish ‘crown of thorns’ be an issue

Answer 20

• feeds on coral- sucess of larva depend on conditions so can get massive boosts in population causing damage
• locally adapted to different conditions so methods of control may have to be different

Question 21

difference of brittle stars to starfish

Answer 21

• more delicate
• ossicles create plate like structures (restricts coelomic canals)
• no ambulacral groove - podia used for feeding not locomotion (no podia/ampullae system)
• even more sophisticated nervous system - ganglia (concentrated nervous tissue) along radial nerves

Question 22

how do brittle stars move

Answer 22

spines on arms and long legs to thrash around and grip substance

Question 23

how do brittle stars feed?

Answer 23

• scavengers
• deposit feeders
• suspension feeders

Question 24

brittle star respiration

Answer 24

bursal slits

Question 25

unique feature of brittle stars

Answer 25

chromatophores in skin so can change colour

Question 26

describe sea urchins ossicles

Answer 26

• ossicles fuse to form a test = hard shell

- modified ossicles form teeth structures

Question 27

how do sea urchins move and breathe

Answer 27

• gills for gas exchange

- spines and podia for movement - move by mutable connective tissue

Question 28

describe an irregular sea urchin

Answer 28

sea potato - have a kind of bilateral system

- use podia for burrowing feeding and respiration

Question 29

sea cucumber structure

Answer 29

• bilateral symmetry
• mouth at top anus at bottom
• radial structure of podia
• small ossicles

Question 30

sea cucumber podia

Answer 30

• modified podia for feeding (suspension and deposit)
• small podia on dorsal surface
• large podia on ventral surface used for crawling/gripping

Question 31

sea cucumber respiration

Answer 31

anus leads into a series of canals (respiratory trees) - breathe through their anus

Question 32

sea cucumber protection

Answer 32

if they are attacked sticky tubules from anus release toxins

Question 33

most ancient group of echinoderms?

Answer 33

sea lilies and feather stars - thought to have body forms of ancient echinoderm

Question 34

describe sea lilies

Answer 34

sessile - collect food using podia on arms which pass food along to mouth
- found in the deep sea

Question 35

describe feather stars

Answer 35

free living
swim with arms
suspension feeders
legs used for support