The Enchinoderms




BIO190: The Class: Echinoderms: Lesson 24

The Enchinoderms

The echinoderms are marine forms and include the sea stars (starfishes), brittle stars, sea urchins, sea cucumbers, and sea littles. They represent a bizarre group sharply distinguished from all other members of the animal kingdom.

Phylum Echinodermata (6 classes)

Have a look at the following sites for an introduction to echinodermata.
Introduction to the Echinodermata
Echinodermata:Morphology
Echinodermata: Life History and Ecology

Characteristics

marine
many benthic
sessile (Class Crinoidea)
unsegmented
radial sym.
(pentamerous)
sensory
1. tactile
2. chemoreceptors
3. photoreceptors
4. statocysts
5. nervous system
  1. varies with group
  2. basic plan of radial nerves
endoskeleton
1. calcium based
  1. ossicles
  2. spicules
  3. pedicellariae
water vascular system
1. tube feet
2. madreporite
locomotion
1. tube feet
2. spines
digestive system
(complete: exception Classes Ophiuroidea & Concentricycloidea and some seastars)
circulatory system
1. greatly reduced
2. mainly circulates coelomic fluids
respiration
1. tube feet
2. respiratory tree
3. bursae
excretory system
(absent)
reproduction
(mostly dioecious)
development
1. fertilization
  (external for most)
2. bilateral larval stages
regeneration of lost body parts

Class Asteroidea (figs. 24-2 --> 24-8) Sea Stars, often called starfishes.

Introduction to the Asteroidea
sea stars
body form
1. central disc
2. radiating arms (broadly shaped near disc becoming more pointed away)
ventral = oral
1. mouth
  1. stomach
    1. cardiac
      (everted for feeding)
    2. pyloric
dorsal = aboral
1. anus
2. madreporite - stone canal - radial canal - lateral canal
  (water vascular system )
3. pedicellariae
ambulacral grooves
1. open
2. tube feet with suckers
3. spines

Class Ophiuroidea (figs. 24-9 --> 24-14)

The brittle stars are the largest of the echinoderms in numbers of species.

brittle stars
5 arms
(slender)
no pedicellariare
closed ambulacral grooves
water vascular system similar to sea stars
tube feet without suckers
madreporite on oral surface

Class Echinoidea (figs. 24-15 --> 24-20)

The echinoids have a compact body enclosed in an endoskeletal test, or shell.

endosketeton = test
1. sea urchin (regular)
  1. long tube feet extening from test
  2. pedicellariae
  3. Aristotle's latern
2. sand dollars and heart urchins (irregular)
  (short spines)

Class Holothuroidea (figs. 24-21 --> 24-24)

The class Holothuroidea (sea cucumbers) contains members that are among the strangest animals, both structurally and physiologically.

sea cucumbers
ossicles
madreporite
cloaca
respiratory tree
self mutilation

Class Crinoidea (figs. 24-25 & 24-26)

The crinoids include the sea lilies and feather stars. As fossil records reveal, crinoids were once far more numerous than they now are.

sea lilies & feather stars
sessile
stalked
fossil record

View this site:
Echinodermata: Fossil Record

Class Concentricycloidea (fig. 24-27)

These disc-shaped little animals were discovered in water over 1000m deep off New Zealand in 1986.

sea daisies
1 cm dia.
disc-shaped
New Zealand (1986)

Once you have completed the lesson, you should go to Assignment 24-1.

E-mail Sylvester Allred at Syl.Allred@nau.edu