Phylum Echinodermata the Echinoderms

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Phylum Echinodermata the Echinoderms Powered By Docstoc
					        Phylum Echinodermata: the
              Echinoderms              Developmental Patterns
                                    All previous animals have been protostomes
                                      Blastopore of blastula develops into mouth
                                      Cleavage is spiral and determinate
                                      Coelom develops via schizocoely
                                    From this point forward, they are
                                      Blastopore develops into anus
Chapter 16
                                      Cleavage is radial and indeterminate
                                      Coelom develops via enterocoely

                                                          Echinodermata: Basics
                                                      >7,000 species
                                                      Exclusively marine
                                                      May be carnivores
                                                      (ex: sea stars),
                                                      detritus feeders (ex:
                                                      sea cucumbers), or
                                                      filter feeders (ex: sea

   Echinodermata: General
Many are radially symmetric (in particular,
pentaradially symmetric)
  Most larvae are bilaterally symmetric
  Thought to have arisen from radially symmetric
Possess an endoskeleton made of calcium
carbonate plates (ossicles)
No head or well-developed brain
  Orientation is referred to as oral (the side with
  the mouth) or aboral (the side away from the
  mouth, with the anus)

      Water Vascular System
Water-filled canals used for locomotion,
attachment to surfaces, and/or feeding
Ring canal surrounds mouth
Madreporite is a sieve-like opening into
the system, connecting to the stone canal
Radial canals branch from ring canal
Lateral canals branch off radial canals
Tube feet at end of lateral canals (often
with suction cups)

   Hemal and Nervous Systems                       Echinodermata: Maintenance
Hemal system consists of strands of tissue
around ring canal and extending into rest         Complete digestive tract
of body                                           Pincerlike pedicellaria on body wall,
  Function not well known; circulates fluid and   which can be used for cleaning, food
  may aid in transporting nutrients, hormones     gathering and protection
  or waste material                               Gases, nutrients, and metabolic wastes
Nervous system includes a nerve net and           (mostly ammonia) diffuse across tube
nerve ring with radial nerves                     feet and other structures
Sensory receptors (light, chemical, and           Coelom important for circulation
mechanical) on body surface and tube feet

                                                 Class Asteroidea:
  Echinodermata: Reproduction
May reproduce asexually or sexually (although        Sea Stars
mostly sexual)                                    >1,500 species
Have ability to regenerate lost arms (common)     Vast majority with 5 arms
or even entire echinoderm if a portion of the     Carnivores; feed on
central disc is present (only in some species)    bivalves, snails,
Most dioecious with external fertilization        crustaceans, cnidarians,
Free-swimming, bilateral larvae
                                                  Often brightly colored
                                                  Move by attaching tube
                                                  feet to a surface then
                                                  pulling body after

                              When eating mussels and other
                              bivalves, sea stars will force
                              open the shell slightly than
                              evert their stomach into the
                              opening. This partially digests
                              the bivalve and helps loosen
                              the adductor muscles.

                                                                The individual above is
                                                                regenerating the oral disk from
                                                                the single long arm. The
                                                                individual to the right is
                                                                regenerating 3 arms.

     Class Ophiuroidea:                                                     Ophiuroidea: General
Brittle Stars & Basket Stars
   >2,000 species (largest                                           Lack pedicellariae
   echinoderm class)
                                                                     Tube feet do not
   Long arms set apart
   noticeably from the
                                                                     have suction disks
   central disk; move in                                             Madreporite is on the
   snakelike motion                                                  oral surface rather
   Brittle stars have non-                                           than the aboral
   branching arms and are                                            surface
   predators or scavengers
                                                                     Mouth has 5 “jaws”
   Basket stars have highly
   branched arms and are                                             for chewing
   filter-feeders                                                    Lack an intestine

    Class Echinoidea: Sand Dollars &           Echinoidea: General
              Sea Urchins                        Characteristics
      ~1,000 species                    Endoskeleton fused into shell, or test
      Sand dollars are                  No arms, but show pentaradial symmetry on
      flattened and live                test
      buried in sediment                Chewing mouth part called Aristotle’s lantern
      Sea urchins are                   Tube feet exit through openings in test
      globular with spines,             Possess pedicellariae with either 2 or 3 jaws
      which may contain
      venom                             Use spines for movement or during burrowing
      Feed on algae, coral,             Eat cookies to a techno beat…
      small sediment-

                                       Class Holothuroidea: Sea Cucumbers
                                       ~1,500 species
                                       Soft, muscular body
                                       (endoskeleton reduced
                                       or absent)
                                       Elongate shape along
                                       oral-aboral axis
                                       Lie on bottom of sea on
                                       one side, move
The picture at right shows tube        sluggishly
feet extending from a sea urchin.
                                       Consume particulate
                                       organic matter

Holothuroidea: General Characteristics                          Holothuroidea: Defense
No arms                                                 Some sea cucumbers have toxic glands in skin
Tube feet reduced to tentacles surrounding mouth and
several rows along top and bottom                       Others possess branches of the respiratory tree
     Tube feet not used for locomotion                  called Cuverian tubules
Respiratory trees pump water through body                  Evert through anus; secrete mucus and/or
Madreporite is internal, and water vascular system is      toxins to entrap predators
filled with fluid from coelom
                                                        Others can expel digestive tract, respiratory
                                                        tree(s), and/or gonads through the anus
                                                           Process is called evisceration

  Class Crinoidea: Sea Lilies and
           Feather Stars
  ~650 species
  Most primitive
  echinoderm class
  Many fossil forms
  Sea lilies are stalked
  and sedentary;
  feather stars swim
  and creep
  All are filter feeders,
  done using the water
  vascular system
  Mouth opens upward