Vein skeleton of a leaf. Skeleton man book pdf contain lignin that make them harder to degrade for microorganisms.
There are two major types of skeletons: solid and fluid. Fluid skeletons are always internal. The exoskeleton of insects is not only a form of protection, but also serves as a surface for muscle attachment, as a watertight protection against drying, and as a sense organ to interact with the environment. An external skeleton can be quite heavy in relation to the overall mass of an animal, so on land, organisms that have an exoskeleton are mostly relatively small. Somewhat larger aquatic animals can support an exoskeleton because weight is less of a consideration underwater.
Pacific Ocean, has a shell that is massive in both size and weight. For additional structure or protection, pliant skeletons may be supported by rigid skeletons. Organisms that have pliant skeletons typically live in water, which supports body structure in the absence of a rigid skeleton. A hydrostatic skeleton is a semi-rigid, soft tissue structure filled with liquid under pressure, surrounded by muscles. Longitudinal and circular muscles around their body sectors allow movement by alternate lengthening and contractions along their lengths. A common example of this is earthworm.
This structure formed is porous and therefore firm and at the same time light. Connected by joints, the individual skeletal parts can be moved by the muscles. This segmental pattern is particularly evident in the vertebral column and the ribcage. Bones in addition to supporting the body also serve, at the cellular level, as calcium and phosphate storage. The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles.