Echinoderms

• the Echindodermata phylum, with echinoderm meaning spiny skin, consists of 7000 living and 20,000 extinct species across seven classes
• asteroida


  sea stars, starfish, sea daisies
• ophiuroidea


  brittle stars
• echinoidea


  sea urchins, sea biscuits, sand dollars
• holothuroidea


  sea cucumbers
• crinoidea


  sea lillies, feather stars
• asexual reproduction in echinoderms


  offspring genetically identical to parent, asteroids, holothuroids, ophiuroids, main methods= fission or autotomy
• fission


  animal splits down fission plane, some develop furrow of weakened tissue and stretch/split
• Stephanasterias abula


  obligate fissiparous reproducers, no gonads
• sclerasterias


  only reproduce by fission as juvelines
• holothuroids asexual reproduction


  twist and stretch body by split fission
• autotomy 


  regeneration of whole animal from breaking off one arm, 1/5 of central disc required, antipredation advantages
• sea stars/ asteroids asexual reproduction

  autotomy
• disadvantages of asexual reproduction in echinoderms 


  energy consuming, slow population increases, reduced dispersal, lack of outbreeding
• advantages of asexual reproduction in echinoderms

  preserves beneficial adaptations, anti-predation, no time spent finding a mate, no resource allocation to gametes (if obligate)
• sexual reproduction in echinoderms

  vast majority show sexual dimorphism, 2 gametes come together to produce offspring with genetics of two individuals, most produce egg/sperm and coordinate release into water column
• pentamorous symmetry 


  5-10 gonads
• asteroids gonads


  2 in each arm
• crinoid


  located on specialised structures called pinnules
• ophiuroid


  in bursae (also where gas exchange occurs)
• holothuroids


  one single internal
• gametes released


  through gonopores
• seasonal breeders


  coincides with algal blooms, provides larvae w/ food supply, shed upwards of 2.5m eggs
• echindoderm larvae


  most species leave to develop in water column, going through range of larval stages before adulthood. possess skeletal rods in pluteus arms for stability and cilia for movement/dispersal
• brood protection echinoderms


  increases survival; embryos/juveniles offered some sort of protection by remaining in association with adult, normally female. not the norm, one species in every group, mainly asteroids and ophiuroids. commonly in cold water species as juveniles brought up in harsh environment, larvae dont survive in cold, produce large yolky eggs to allow larvae to grow/develop into larger size before independence
• brooding in asteroids


  brood eggs under arched body, brooding basket formed by spines, tube feet to manipulate eggs: oxygenate and clean
• Diplasterias brandti


  asteroids: brood eggs until hatch as juveniles
• asterina gibbosa


  asteriods: lay under/ attach eggs to rocks for protection
• leptisterius


  asteroids: lay and fertilise eggs, eat them, brood eggs in stomach, undergoes physiological changes; prevents animal from eating as it switches off enzyme production, definitive cost
• brooding in ophiuroids


  bursae used as brood pouches, large broods can restrict/prevent feeding
• amphipholus squamate


  ophiuroids: no known larvae stage exists, young emerge as juveniles
• brooding in echinoids


  external brooders, carry eggs between spines or around peristome surrounding aristotle's lantern
• brooding in holothuroids


  brood eggs internally, juveniles exit through ruptures in body wall, viviparity
• synaptula hydriformis


  holothuroids: provide young with additional nutrients
• crinoids


  eggs stuck to pinnules, some show internal brooding in pouches or pinnules (antedon genus)
• disadvantages of broodcare in echinoderms


  feeding may be reduces, fecundity decreased due to large egg size, large eggs expensive to produce, reduced dispersal of young
• advantages of brood care in echinoderms


  increased chances of offspring survival, increased parental fitness
• disadvantages of sexual reproduction in echinoderms


  high energy investment, resource competition, low fertilisation rate (external)
• advantages to sexual reproduction in echinoderms

  genetic diversity