Invertebrates are organisms that do not have backbones, however, many of them have special internal or external skeletons that are made of various materials and can fit their functions depending on the environment of the organism. Some animals have crystalline structures, others have cuticles, an outer covering for arhthropods, others have internal structures that contain high internal pressures, among others.
These designs are all specific for adapting to the changes within their environment and the way that they gather and hunt for their prey.