Make your own free website on Tripod.com
Skeletal System
Types of Skeletons

HOME

Pre-Quiz
Types of Skeletons
Joints
Skeletal Functions
Types of Bones
Structure of Long Bones
Microscopic Structure
Skeletal Development
Axial Skeleton
Appendicular Skeleton
Interactive Skeleton
Diseases, Disorders and Fractures
Links
Post-Quiz

Hydrostatic Skeletons:
- consists of fluid held under pressure in a closed body compartment
- main type of skeleton in most Cnidarians, Flatworms, Nematodes and Annelids
- can control their form and movement by changing the shape of the fluid filled
      compartments with muscles in the body wall
- offer no protection of support for large land animals
 

Example of Hydrostatic Skeleton
hydroskel1.gif
The Sea Anemone has a hydrostatic skeleton & can change its shape by contracting a set of muscles.

Exoskeletons:
- a hard encasement deposited on the surfave of an animal
- as the animal grows, the exoskeleton changes size by the enlargement of the
       diameter of the shell when new layers are added to the outer edge
- Cuticle (a polysaccharide similar to cellulose) makes up almost half of the cuticle. 
       Fibrils of the chitin are embedded in  a matrix made of protein and form composit
       material which increases the flexibility and strength of the exoskeleton.
- hardened via the addition of organic compounds and non-organic salts
- as the organism grows the exoskeleton must be molted and relaced by a larger
       one.
- Typically seen in arthropods and mullusks

Example of Exoskeleton
exoskeleton.gif
Arthropods, such as this mite, have exoskeletons creating hard shells on the outside of their body.

Endoskeletons:
- consists of hard supporting elemnts buried within the soft tissues of an animal
-Characteristic of Sponges, echinoderms and chordates
        -Sponges have hard spicules of inorganic material or softer protein fibers to
           reinforce them.
       -Echinoderms have hard plates beneath their skin called ossicles which are
           either tightly bound together by protein fibers (ex: sea urchins) or loosely
           bound for changing shape (ex: sea stars).
       -Chordates have endoskeletons of bone and/or cartilage.  The mammalian
           skeleton consists of over 200 bones and is divided into the Axial and
           Appendicular skeletons.

Example of Endoskeleton
fetus.gif
Humans contain endoskeletons, as seen in this picture of a human fetus.