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

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
    

  • 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
  

• 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
  

• 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.
        

    • 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