Insect Diversity Subphylum Uniramia is an enormous group of mostly terrestrial arthropods that have chewing mouthparts called mandibles (jaws). Uniramians consist of three classes: Insecta (insects), Diplopoda (millipedes), and Chilopoda (centipedes). Insects are the largest group of organisms on Earth, with more than 700,000 named species.

Orders of Insects Order Examples Number of species Coleoptera “shield winged” Beetles, Weevils 350,000 Diptera “two winged” Flies, Mosquitoes 120,000 Lepidoptera “scale winged” Butterflies, Moths Hymenoptera “membrane winged” Ants, Wasps, Bees 100,000

Insects Insects are primarily a terrestrial group, and aquatic insects probably had terrestrial ancestors. Although the great majority of insects are small, others are much larger. Generally, the larger insects live in tropical areas. Despite great variation in their size, all insects share the same general body plan, made up of three body sections.

Insect Body Plan Head Located on an insect’s head are mandibles, specialized mouthparts, and one pair of antennae. The mandibles and mouthparts of different insect species are adapted for eating different foods. An insect’s head usually has a relatively large pair of compound eyes and a pair of antennae. Like the mouthparts, antennae vary greatly in size and shape.

Insect Body Plan Thorax The thorax is composed of three fused segments. Attached to the thorax are three pairs of jointed walking legs. Some insects, such as fleas, lice, and silverfish, lack wings, but other adult insets have one or two pairs attached to the thorax.

Insect Body Plan Abdomen The abdomen is composed of 9 to 11 segments. In adult insects, there are no wings or legs attached to the abdomen.

Insect Life Cycle The life cycles of most insects are complex, and often several molts are required before the adult stage is reached. During the last molt, the young insect undergoes a dramatic physical change called metamorphosis.

Complete Metamorphosis Almost all insect species undergo “complete” metamorphosis. The wingless, wormlike larva encloses itself within a protective capsule called a chrysalis. Here, it passes through a pupa stage, in which it changes into an adult.

Incomplete Metamorphosis A smaller member of species develop into adults in a much less dramatic incomplete metamorphosis. In these species, the egg hatches into a juvenile, or nymph, that looks like a small, wingless adult. After several molts, the nymph develops into an adult.

Flight Insects were the first animals to have wings. For more than 100 million years, until flying reptiles appeared, insects were the only flying organisms. Flying insects were able to reach previously inaccessible food sources and to escape quickly from danger. Basic motion of the insect wing in insect with an indirect flight mechanism scheme of dorsoventral cut through a thorax segment with a wings b joints c dorsoventral muscles d longitudinal muscles

Flight An insect’s wings develop from saclike outgrowths of the body wall of the thorax. The wings of adult insects are composed entirely of chitin, strengthened by a network of tubes called veins (which carry air and a bloodlike substance). In most insects, the power stroke of the wing during flight is downward, and it is produced by strong flight muscles. When at rest, most insects fold their wings over their abdomen, but a few insects are unable to do this. Most insects have two pairs of wings. A few groups of insects, such as fleas and lice, are wingless.

Flight In most insects only one pair of wings is functional for flight. In some species, the second pair of wings serves another purpose. In grasshoppers and beetles, the forewings act as protective wing covers. In flies, the hindwings are modified into knoblike structures that help control stability during flight.

Social Insects Two orders of insects, Hymenoptera (ants, bees, and wasps) and Isoptera (termites), have elaborate social systems. These insects often live in highly organized societies of genetically related individuals. Within these insect societies, there is a marked division of labor, with different kinds of individuals performing specific functions. The role played by an individual in a colony is called its caste. Caste is determined by a combination of heredity, diet (especially as a larva), hormones, and pheromones (chemical substances used for communication).

Insect Relatives Centipedes and Millipedes have similar bodies. Each has a head region followed by numerous similar segments. Each segment bears one or two pairs of legs. Centipedes have one pair of legs per segment and can have up to 173 segments. Modern millipede segments have two pairs of legs. While centipedes are carnivores, most millipedes are herbivores.

Comparison of Crustaceans and Insects Characteristic Crustaceans Insects Nature of Appendages Most are branched at the end Unbranched at the end Antennae Two pairs One pair Chewing Appendages Usually three pairs Location of Appendages Cephalothorax and Abdomen Head and Thorax Respiration Gills Tracheal System

Subphylum Trilobitomorpha NB #111 Lived from 600 MYA to 345 MYA Dominant life form while they lived Fed on annelids, molluscs, and detritis (decaying organic matter) Body flat and divided into three segments: Head, thorax, and pygidium Could roll into a ball for protection (kind of like an arthropod of today) Branched appendages possibly used for walking, digging, or swimming

Subphylum Crustacea Includes crayfish, shrimp, lobsters, and crabs All aquatic…. Except some isopods and crabs Differences from other arthropods.. 2 pairs of antennae (other arthropods have 1) Biramous appendages Segments with two rami (structure that gives appendage a Y shape)

Subphylum Crustacea Class Malacostraca Largest class of crustaceans Crabs, lobsters, crayfish, shrimp, mysids, shrimplike krill, isopods, and amphipods

Subphylum Crustacea Class Malacostraca Crayfish: General crustacean characteristics Two body regions: Cephalothorax Fused head and thorax Abdomen Posterior Locomotor and visceral functions Form of a muscular tail

Subphylum Crustacea Class Malacostraca Crayfish: Paired appendages present in both body regions Two pairs of antennae 3rd-5th pairs associated with the mouth 3rd pair modified into mandible Chews and grinds food 4th & 5th pairs called maxillae Food handling 6th – 8th- maxillipeds- handle food 9th-13th- pereopods- walking legs 1st pereopod is a cheliped (large pincher)

Subphylum Crustacea Class Malacostraca Crayfish: Diet- other invertebrates, plant matter, and dead or dying organisms Large stomach specialized for grinding (foregut) Digestive gland secretes digestive enzymes to break down food Gills- located in chambers Sensory structures: Compound eyes, simple eyes, statocysts, chemoreceptors, proprioceptors, and tactile setae

Subphylum Crustacea Class Malacostraca Crayfish: Excretion: Green glands or antennal glands (actually green in color) Reproduction: Dioecious Mate after female has molted Male flips the female on her back Fertilzation occurs after copulation Sperm deposited on female Eggs are sticky and secure to the female’s pleopods

Subphylum Crustacea Class Branchiopoda Primarily live in freshwater Fairy shrimp and brine shrimp Flattened, leaflike appendages used in… Respiration Filter feeding Locomotion

Subphylum Crustacea Class Maxillopoda Short bodies and a unique combination of 5 head, 6 thoracic, and 4 abdominal segments, plus a telson Copepods- abundant (vector for Guinea worm) Barnacles- sessile & may colonize on ships Mostly marine Copepod Barnacles

Subphylum Chelicerata Spiders, mites, ticks, horseshoe crabs, and sea spiders Two tagmata Prosoma (cephalothorax) Sensory Feeding Locomotion Opisthosoma Digestion Reproduction Excretion Respiratory organs