EVERYDAY SCIENCE

Detailed explanation-1: -The distinguishing feature of arthropods is the presence of a jointed skeletal covering composed of chitin (a complex sugar) bound to protein. This nonliving exoskeleton is secreted by the underlying epidermis (which corresponds to the skin of other animals).

Detailed explanation-2: -The phylum Arthropoda contains a wide diversity of animals with hard exoskeletons and jointed appendages. Many familiar species belong to the phylum Arthropoda-insects, spiders, scorpions, centipedes, and millipedes on land; crabs, crayfish, shrimp, lobsters, and barnacles in water (Fig. 3.72).

Detailed explanation-3: -All arthropods have jointed legs, claws, and body segments! Arthropods have segmented bodies. Each body segment usually has a pair of appendages. The appendages can be antennae, wings, legs, or mouthparts!

Detailed explanation-4: -Long, jointed limbs would hardly seem to be an evolutionary innovation, but they and other jointed appendages account for the great freedom of movement enjoyed by terrestrial arthropods and vertebrates. Without skeletons, most soft-bodied animals creep or writhe over surfaces by contracting muscles of the body wall.

Detailed explanation-5: -As mentioned earlier, the appendages of arthropods are distinct from those of annelids in that they are jointed. In some species, the appendages are also branched, a condition called biramous. Unbranched appendages are called uniramous. Jointed appendages allow the animal much greater flexibility and range of movement.