Phylum Echinodermata Introduction

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Phylum EchinodermataIntroduction
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Echinodermata

• About 6000 species, all marine

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Echinodermata Major characteristics

• secondary pentamerous radial symmetryinternal
  skeleton
• water vascular system

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Water Vascular System

• Madreporite
• stone canal
• ring canal
• radial canal
• lateral canals
• Ampulae
• tube feet

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CLASSIFICATION OF ECHINODERMATA

• Class Asteroidea
• Class Ophiuroidea
• Class Echinoidea
• Class Holothuroidea
• Class Crinoidea

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Class AsteroideaTrue Starfishes
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Class Asteroidea True Starfishes

• arms not sharply delineated from central disc
• tube feet with suckers used for
• Locomotion
• obtaining food
• madreporite and anus aborally located
• some have pedicellariae - jawlike appendages of
  epidermis

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Class Asteroidea True Starfishes

• Feeding
• Mouth
• cardiac stomach- can be extruded
• pyloric stomach
• pyloric caecae
• Anus
• feed primarily on sessile organisms

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Class Asteroidea Systems

• Circulation
• poorly developed with fluid filled chambers
• no heart coelom ciliated for fluid movement
• Excretion
• no special organs
• general diffusion across body surfaces like tube
  feet
• Respiration
• no special organs
• across body membranes
• Nervous System
• associated with epidermis
• circular oral nerve ring with branches into arms

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Asteroidea Body wall

• Epidermis- outer surface includes
• mucous cells
• epithelium
• Pedicellariae- jawlike appendages of the
  epidermis
• can open and close
• used to clean body of debris or put debris on
  body
• Dermis- includes
• nerve cells
• connective tissue
• Skeleton- below dermis
• made of ossicles
• lattice like connections
• Calcium carbonate
• with spines and tubercles
• Muscle layer- below dermis
• Peritoneum that lines coelom

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Asteroidea Reproduction

• are dioecious external fertilization
• usually 10 gonads 2 in each arm
• have fissiparity- division of central disc into
  two animals

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Asteroidea Reproduction

• free living larvae
• bipinnaria- first larval form develops into
• brachiolaria - shows development of arms

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Class OphiuroideaBrittle Starfishes
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Class OphiuroideaBrittle Starfishes and Basket
Stars

• 5 arms usually
• central disc well marked off, no branches of gut
  in arms

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Class OphiuroideaBrittle Starfishes and Basket
Stars

• no anus, no ambulacral groove
• madreporite on oral surface
• no suckers on tube feet, no ampullae (have a
  valve to control pressure)
• no pedicellariae
• able to move quickly and snake like hence their
  class name

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Class Echinoideasea urchins, sea bisquits, sand
dollars
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Class Echinoidea

• no arms
• skeleton is fused into a solid test
• tube feet have suckers
• covered with moveable spines and pedicellariae

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Class Echinoidea
specialized mouth structures - Aristotle's
Lantern
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Class Holothuroidea Sea cucumbers
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Class Holothuroidea Sea cucumbers

• body elongated in oral-aboral axis
• skeletal system reduced or absent
• no spines or pedicellariae
• mouth and anus at opposite ends of body

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Class Holothuroidea Sea cucumbers

• no external madreporite
• tube feet with suckers
• respiration through anal respiratory tree
• dioecious single gonad
• suspension or detritus feeders
• commensal relationship with pearl fish

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Class Crinoidea Sea Lillies
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Class Crinoidea Sea Lillies

• most are extinct
• most primative
• all sessile, with stalk that attaches to
  substrate
• have branched arms for filter feeding
• no suckers on tube feet
• no madreporite
• no pedicellariae