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

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