Lecture 13 - Echinoderms Flashcards
what 3 things define a deuterostome
- radial and indeterminate cleavage
- folds of archenteron form coelom
- anus develops from blastopore
echinoderms have pentamerous radial symmetry - describe
body divided into 5 parts - not related to other radially symmetrical groups
describe the larvae of echinoderms
larvae = bilaterally symmetrical - this is a useful feature of sessile animals to distribute their larva
- larvae show convergent evolution
what is unusual about echinoderms which occurs despite their radial symmetry?
they have hox genes which they express in a particular order
- homeotic mutations can cause more limbs
echinoderm internal skeleton and how it is advantageous
- 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
what is a unique feature of echinoderms and another way it can be used
ossicles - can be fixed and hinged forming a casing around animals e.g sea urchins - can be absent/ tiny e.g. sea cucumbers
what does echinoderm mean?
spiny skin
podia
- tube feet
- large podia = locomotion + feeding
- small podia = respiration + suspension feeding
water vascular system
- 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)
how do sea urchins and star fish grip
sea urchin = suction cap at end of podium
star fish = chemical reaction - can feel different substances and move differently on them
mutable connective tissue
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
what is a weird way echinoderms can protect themselves
can release their internal organs out of body to satisfy predator and then regenerate them
5 echinoderm groups (exclusively marine)
- asteroidea (starfish)
- ophiuroidea (brittle stars)
- Echinoidea ( sea urchins)
- holothuroidea (sea cucumbers)
- crinoidea (sea lillies + feather stars)
where is the mouth found in star fish?
mouth on underside and anus on top
what is the ambulacral ridge in star fish
on the middle of the legs where the podia are found
what are the pedicellaria in star fish?
pincers that remove any waste on the body
what is the papula in star fish?
skin gills- projection of coleom which serves in gas exchange and excretion
how do starfish feed
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
star fish nervous system
- 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
why can the starfish ‘crown of thorns’ be an issue
- 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
difference of brittle stars to starfish
- 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
how do brittle stars move
spines on arms and long legs to thrash around and grip substance
how do brittle stars feed?
- scavengers
- deposit feeders
- suspension feeders
brittle star respiration
bursal slits
