A true endoskeleton develops from mesodermal tissue. Such a skeleton is present in echinoderms and chordates. The Coleoidae do not have a true endoskeleton in the evolutionary sense; here, a mollusc exoskeleton developed into several sorts of internal structure, the "cuttlebone" of cuttlefish being the best-known version. An important advantage of an endoskeleton over an exoskeleton is that the endoskeleton provides more structural support.
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