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Section 28-1: Introduction to the Arthropods
Arthropods have a segmented body, a tough exoskeleton, and jointed appendages.
In many groups of arthropods, continuing evolution has led to fewer body segments and highly specialized appendages for feeding, movement, and other functions.
When they outgrow their exoskeletons, arthropods undergo periods of molting.
Section 28-2: Groups of Arthropods
Arthropods are classified based on the number and structure of their body segments and appendages, particularly their mouthparts.
Crustaceans typically have two pairs of branched antennae, two or three body sections, and chewing mouthparts called mandibles.
Chelicerates have mouthparts called chelicerae and two body sections, and most have four pairs of walking legs.
Uniramians have jaws, one pair of antennae, and unbranched appendages.
Section 28-3: Insects
Insects have a body divided into three parts—head, thorax, and abdomen. Three pairs of legs are attached to the thorax.
The growth and development of insects usually involve metamorphosis, which is a process of changing shape and form. Insects undergo either incomplete metamorphosis or complete metamorphosis.
Ants, bees, termites, and some of their relatives form complex associations called societies.
Section 28-4: Echinoderms
Echinoderms are characterized by spiny skin, five-part radial symmetry, an internal skeleton, a water vascular system, and suction-cup-like structures called tube feet.
The water vascular system carries out many essential body functions in echinoderms, including respiration, circulation, and movement.
Classes of echinoderms include sea lilies and feather stars, sea stars, brittle stars, sea urchins and sand dollars, and sea cucumbers.