Echinodermata

• Phylum Mollusca, Phylum Annelida, Phylum Arthropoda, Phylum Echinodermata, Phylum Chordata are coelomate animals/eucoelomates
• Phylum Urochordata and Phylum Cephalochordata are other phyla
• Phylum Vertebrata is a subphylum of Phylum Chordata
• Phylum Echinodermata


  • Have an internal skeleton of calcium carbonate
  • Ossicles vary in size and structure and are manufactured by specialized cells
  • Have a separate coelom used with interconnecting fluid filled tubes and canals
  • Have a ring canal that circles the mouth and gives off 5 radial canals

  
• Water Vascular System


  A complex series of fluid-filled canals with numerous flexible feeding and locomotory appendages
• Body form of echinoderms

  • Radial symmetry
  • Oral vs aboral surface
  • No distinct head
  • Pentamerous radial symmetry in most
• Body wall of echinoderms

  • Outer surface covered by epidermis
  • Below epidermis is thick dermis
  • Ossicles have bony projections for defense
  • Beneath dermis is layer of outer circular and inner longitudinal muscle
  • True coelom lined with peritoneum
• Movement and food gathering

  1. Predominantly done by water vascular system

  2. A second, separate coelomic compartment unique to echinoderms

  3. Derived from coelom and lined with ciliated epithelium

  4. Whole system operates hydraulically

  
• Madreporite


  • Calcareous deposits just inside and around the mouth
  • Internal canals connection to the outside
• Radial Canals


  • Branch off ring canal
  • Lateral canals branch off radial canals
  • Ampullae lead to small muscular sacs that serve as fluid reservoirs
• Tube feet


  • The tip of the tube feet are flattened, forming suckers
  • Used to cling to substrates, move and to feed
  • Concentrated in ambulacral groove
• Feeding and digestion in echinoderms

  • Particle feeders
  • Predators
  • Scavengers
  • No parasitic species
• Digestive system


  • Simple, usually complete digestive tract
  • Stomach has 2 chambers
  • Digestive enzymes secreted into stomach by pyloric caeca
• Respiration


  Dermal branchae/papulae exchange respiratory gases
• Circulation


  • Coelomic circulation
  • Dermal branchiae (or papulae) - tiny saclike projections extend through epidermis
  • Have a blood vascular system (hemal system) with heart but it's usually rudimentary and its function unclear
• Nervous system


  • No brain or centralized processing area
  • Tube feet are innervated
  • Circumoral ring and radial nerves branching from it help coordinate movement of arms and movement of the starfish
• Protection


  Many starfish have small jaw-like pedicellariae on body surface to protect against animals and debris

  
• Excretion


  • Removal of nitrogen wastes (mainly ammonia) through body surface, dermal branchiae/papullae, tube feet
  • Amoeboid cells can also engulf nitrogen wastes and move them to the outside
• Reproduction


  1. Dioecious

  2. Produce characteristic ciliated, free-swimming, planktonic larva

  3. External fertilization

  4. Some can reproduce asexually by fragmentation

  5. Many have excellent powers of regeneration
• A wide variety of other animals make their homes in or on echinoderms, including algae, protozoa, ctenophores, turbellaria, barnacles, copepods, decapods, snails, clams, polychaetes, fish and other echinoderms