This illustration shows a crab, a species of cancer. Crabs are decapod crustaceans with thick exoskeletons.

Crab

This illustration shows a crab, a species of cancer. Crabs are decapod crustaceans with thick exoskeletons.

Section through insect crust, showing layers of chitin at <em>c</em>, the cellular layer or hypodermis at <em>h</em>, and basal membrane at <em>b</em>.

Insect Crust

Section through insect crust, showing layers of chitin at c, the cellular layer or hypodermis…

"Single zooid with the adjacent soft tissues as seen after removal of the exoskeleton by decalcification. Z1, the distal, and Z2, the proximal of intracalicular portion of the zooid; ec, ectoderm; ct, coenenchymal tubes; sp, superficial network of solenia." &mdash;Encyclopedia Britannica, 1910

Zooid

"Single zooid with the adjacent soft tissues as seen after removal of the exoskeleton by decalcification.…