An
endoskeleton is an internal support structure of an
animal, composed of
mineralized tissue. Endoskeleton develops within the skin or in the deeper body tissues. The vertebrate is basically an endoskeleton made up of two types of tissues. During early embryonic development the endoskeleton is composed of
notochord and
cartilage. The notochord in most vertebrates is replaced by vertebral column and cartilage is replaced by bone in most adults.In three
phyla and one
subclass of animals, endoskeletons of various complexity are found:
Chordata,
Echinodermata,
Porifera, and
Coleoidea. An endoskeleton may function purely for support, but often serves as an attachment site for muscle and a mechanism for transmitting muscular forces. A true endoskeleton is derived from
mesodermal tissue. Such a
skeleton is present in echinoderms and chordates. The poriferan 'skeleton' consists of microscopic calcareous or siliceous
spicules or a
spongin network. The Coleoidae do not have a true endoskeleton in sense; here, a
mollusc exoskeleton evolved into several sorts of internal structure, the "cuttlebone" of
cuttlefish being the best-known version. Yet they do have cartilaginous tissue in their body, even if it is not mineralized, especially in the head, where it forms a primitive cranium.The endoskeleton gives shape,support and protection to the body and provides a mean of locomotion.