(1) The advantage of an internal skeleton is that it allows the animal to grow much larger than is the case with the arthropod type exoskeleton .(2) In these specimens the external surface of the exoskeleton is present, unless complete or partial exfoliation is noted.(3) The hard parts may be mineralized, as in the shells of bivalves, or composed of organic material, such as the chitin that makes up the exoskeleton of arthropods.(4) Lobsters, like all animals with exoskeletons , periodically shed their armor as they grow.(5) They considered the specimen to be testate, but where the cranidium is broken on the right posterolateral corner, there is no sign of an exoskeletal layer.(6) The trilobites comprise a major class-level clade of extinct marine arthropods characterized by calcareous, multisclerite, dorsal exoskeletons .(7) Both have sophisticated recognition abilities based on olfactory cues emanating from the exoskeletal cuticle.(8) Mud crab exoskeletal remains were abundant in the scat of river otter of the upper Parker River estuary.(9) In this paper we report the discovery of a nearly complete trilobite fossil over 680 mm long that yields a reconstructed exoskeletal length of more than 720 mm.(10) One modification in trilobites might be that the selection was primarily for exoskeletal morphology rather than limb structure.
