Hydrostatic Skeleton of invertebrates:
Hydrostatic (Hydro=water + statikos=to stand).
Skeleton of invertebrates is a core of liquid (water or a body fluid such as blood) surrounded by a tension resistant sheath of longitudinal or circular muscles. It is similar to water filled balloon because the force exerted against incompressible fluid in one region can be transmitted to their regions. Contracting muscles push against hydrostatic skeleton and the transmitted force generates body movements as the movement of sea anemone. Lumbricus (earth worm) contracts its longitudinal and circular muscles alternately creating a rhythm that moves the earthworm through the soil. In both of these examples hydrostatic skeleton keeps the body from collapsing when its muscles contract. Invertebrate hydrostatic skeleton can take many forms and shapes such as gastrovascular cavity of acoelomates, a rhynchocoel in nemertines, a pseudocoelom in aschelminthes, a coelom in annelids or a hemocoel in molluscs.
Vertebrates: Vertebrates have cartilage and bone.
Cartilage: It is speciailized type of connective tissue that provides a site for muscle attachment, aids in movement at joints and provides support. Like other connective tissues, it consists of cells (chondrocytes), fibres and cellular matrix.
Bone: Bone (osseous) tissue is a specialized connective tissue that provides a point of attachment for muscles and transmits the force of muscular contraction from one part of the body to another during movement. In addition bones of the skeleton support the internal organs of many annelids, store reserve calcium and phosphate and manufacture red blood cells and some white blood cells.
Human endoskeleton has two major parts, the axial skeleton and appendicular skeleton. The axial skeleton is made up of skull, vertebral column, sternum and ribs. Appendicular skeleton is composed of appendages (fore limbs and hind limbs), pectoral girdle and Hind limbs. These girdles attach the upper and lower appendages to axial skeleton.