The Echinoderms

Phylum Echinodermata

Class Crinoidea

Class Asteroidea

Class Ophiuroidea

Class Echinoidea

Class Holothuroidea

Evolved from bilaterally symmetrical animal; have bilateral larvae BUT radial symmetry.

Characteristics of Group:

1. spiny, calcareous endoskeleton of plates or tiny ossicles

2. dermal branchiae or papulae

3. pedicellariae

4. water vascular system

5. radial or biradial symmetry

6. most bottom dwellers and marine

Class Asteroidea - sea stars or starfishes

Central body (central disc) with rays or arms

Oral side = mouth vs aboral side (rough or spiny)

ambulacral grooves run from central disc out each arm; Grooves bordered by tube feet

1. Endoskeleton - under epidermis - mesodermal

Ossicles bound together with connective tissue Spines project from ossicles

2. Dermal papulae or dermal branchiae or skin gills found on aboral side

projections of coelomic cavity covered by thin epidermis

respiration

3. Pedicellariae

4. Water Vascular System

Another coelomic compartment - unique to echinoderms

Canals and tube feet - locomotion, food gathering, respiration, and excretion

Madreporite - aboral side-------------->>Stone canal------->> Ring canal--------->> Radial canals------->> Lateral canals--------->>Tube feet (inner end-- ampulla, outer end --sucker)

5. Digestive System

Mouth on oral side (faces down)--------->> short esophagus---------->> large stomach = cardiac and pyloric portions Cardiac - can be everted during feeding

Pyloric - connected to digestive glands or pyloric ceca in each arm

6. Nervous System

nerve ring in central disc radial nerves in each arm ocellus at tip of each arm.

7. Reproduction

gonads in arms dioecious with external fertilization

regeneration autonomy

Class Ophiuroidea - brittle stars

No pedicellariae and no papulae

Ambulacral grooves are closed - no ampullae

Class Echinoidea - sea urchins and sand dollars

dermal ossicles fit together to form plates (test). Tube feet extend through pores in plates.

Regular - radial symmetry - sea urchins

Irregular - secondarily bilateral - sand dollars

Aristotle's Lantern

Ambulacral grooves closed and water vascular system runs beneath test.

Class Holothuroidea - sea cucumbers

hydrostatic skeleton

respiratory tree unique to this group

Class Crinoidea - sea lilies and feather stars

Primitive forms. Sessile most of life. Most stalked - look like flowers.