Echinoderms

Characteristics of Echinoderms

  • Don't look/act like animals initially, they are

    • They move, attack prey, defend themselves, but tend to just be very slow about it
  • They all share:

    • Radially symmetrical body divided into five parts
    • Move have hundreds of tiny tube feet to crawl/climb
    • Most have a water vascular system that brings oxygen to the body cells
  • Echinoderms have some traits close to chordates:

    • Adult is radially symmetrical
    • Larvae is bilaterally symmetrical
    • Bilateral symmetry, along a vertical axis, is what mammals, fish, etc. have

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Class Crinoidea

  • Includes feather stars and sealilies
  • Primary characteristics of this class:
    • Long, feather-like arms and short, hook-like legs called cirri
    • Upward facing mouths \n
    • Most nocturnal feeders, at night they unfurl their arms to capture plankton and nutrients carried into their paths by the current
    • By day, they coil up tightly and hide in the reef 
    • Most crinoids attach to the bottom by their cirri

Class Asteroidea

  • Sea stars belong to this class \n
  • Primary characteristics of this class:
    • Predators w/ downward facing mouths 
    • Tube feet covering their undersides
    • Usually have five arms
    • Few species have toxic spines for protection
    • Each arm carries an equal share of the animal's systems and organs
    • They can regenerate a lost limb, some grow into several new animals when cut into pieces

Class Ophiuroidea

  • Sand dollars/sea urchins belong to this class
  • Primary characteristics of this class:
    • Possess a five-sectioned body with no arms
    • Sand dollar/sea urchins share a disk-shaped body
    • Tube feet on the underside
    • Sea urchins graze on algae
    • Swimmers avoid sea urchins because of spines
    • Some species have toxins in the spines for self defense
    • Urchins can move their spines/tube feet for locomotion
  • Shell is called a test 

Class Holothuroidea

  • Sea cucumbers are part of this class \n
  • Primary characteristics of this class:
    • Have elongated five segment body with tentacles around the mouth
    • Most feed by moving with their mouths open, allowing sand to flow through; a few are filter feeders
    • Some expel a sticky mass of white tubes covered in toxin
    • Protected by tough skin and the ability to expel part of their internal organs for predators while saving the rest to survive
    • They're also flshy. The things on them that look like spines are actually soft
    • Carnivorous
    • They invert their stomach through the mouth to envelope food
    • Intestine is short/missing
      • Sea urchins/sea cucumbers are the exception due to them feeding off plants
    • Body cavity is filled with a coelomic fluid
      • Coelomic - From the coelom, which is the main body cavity in most animals and is positioned inside the body to surround/contain the digestive tract and other organs. \n
    • Also serves to bring in oxygen
    • Sea cucumbers bring in water through anus to the respiratory branches
      • Extension of guts

Echinoderm Reproduction

  • Echinoderms have separate sexes with 5, 10, or more gonads that shed sperm/eggs

    • Spawning
    • Gametes do not survive long in the water
    • Individual spawn all at once
    • Fertilized eggs develop into plankton and results in a ciliated larva
    • Some echinoderms carry eggs
  • Asexual reproduction

    • Fission
    • Central disk splits into 2 new individuals
    • Regeneration
    • Ability to regrow missing parts
    • Requires that part of the central disk be present to grow a new individual
    • Sea stars do not require the disk 

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