Transcript Echinoderms & Invertebrate Chordates

Echinoderms
Section 38.1
Echinoderms
 Examples:
sea stars, sand dollars, sea
urchins, & sea cucumbers
 Marine environments
 Brilliantly colored
 Radial symmetry
4 Unique Characteristics:
1.
Ossicles: calcium carbonate plates that
make up exoskeleton
2.
Water-vascular system: network of
water-filled canals inside body
3. Tube feet: small, movable extension of
w-v system which aid in movement,
feeding, respiration, & excretion
4. Pentaradial symmetry: body parts
extend from center along 5 spokes
Classification
6
classes of echinoderms (only 5
discussed in textbook):
 Class
Crinoidea
 Class Ophiuroidea
 Class Echinoidea
 Class Holothuroidea
 Class Asteroidea
Class Crinoidea
 Examples:
sea lilies, feather stars
 Crinoid means “lily-like”
 5 main arms that branch to form up to 200
more arms
 Filter feeders
 Mouth faces up
Class Ophiuroidea
 Largest
class with examples such as
basket stars & brittle stars
 Ophiuroidea means “snake-tail”
 Live on bottom of ocean
 Regeneration of broken arms
 Long, narrow arms allow for quick
movement
Class Echinoidea
 Examples:
sea urchins & sand dollars
 Echinoidea means “spinelike”
 Compact, rigid endoskeleton that
surrounds internal organs
 Spines can have barbs or venom
Class Holothuroidea
 Example:
sea cucumber
 Holothuroidea means “water polyp”
 Armless
 Ossicles are not connected thus soft
bodies
 Tentacles around mouth to capture prey
Class Asteroidea
 Example:
sea star (starfish)
 Asteroidea means “starlike”
 Variety of sizes, shapes, and colors
 Compete with humans for oysters, clams,
etc
Sea Stars
Section 38.1 continued
External Structure
 Several
arms extending from central
region
 Two rows of tube feet on underneath side
of each arm
 Oral

surface: side where mouth is located
Starfish = underside
 Aboral
surface: side opposite of mouth
 Rough
texture due to short spines
 Pedicellariae: tiny pinchers surrounding of
each spine that keep body free of foreign
objects
Water-Vascular System
 Network
of water-filled canals that are
connected to the tube feet
 Water

movement:
Madreporite (sievelike plate on aboral
surface)  stone canal  ring canal
(encircles mouth)  radial canal (extends to
each arm)  tube feet
 Ampulla:
bulblike sac at end of tube feet
that allows for movement and suction
Feeding & Digestion
 Prey:
mollusks, worms, clams
 Cardiac stomach: can be turned inside out
through mouth during feeding
 Digestive

pathway:
Mouth  cardiac stomach  pyloric stomach
 digestive glands in each arm  anus
Other Body Structures
 No
circulatory, excretory, or respiratory
systems!
 Skin gills: thin walls of tube feet that allow
gas exchange
 Nervous system = nerve ring (around
mouth), radial nerves (length of each arm),
eyespots (end of each arm), tentacles
Reproduction & Development
 Separate
sexes – each arm has sex
organs
 External fertilization

After 2 months of swimming they settle to
bottom of ocean and metamorphous into adult
 Regeneration

(asexual)
As long as part of the central region stays in
tact