Insects

Class Insecta

Most numerous and diverse of all the groups of arthropods.

• (There are more species of insects than species in all the other classes of animals combined!!)

» Have three pairs of legs » Usually have two pairs of wings on the

thoracic region of the body, (although some have one pair of wings, or none)

» Body organization: head, thorax, and abdomen.• The head usually bears a pair of

large compound eyes, a pair of antennae, and usually three ocelli (simple eyes).

• General Characteristics– Segmented bodies – Jointed appendages

• Specialized for eating, sensing, reproduction, defense and movement

– Exoskeleton• Hard covering on the outside of the

animal• Limits the growth of the organism (must

shed)• Muscles are attached to this layer• Contains protein, lipid, chitin, and often

calcium carbonate • secreted by underlying epidermis and

shed (molted) at intervals

– Bilateral symmetry – Muscular system complex (contains

both striated and smooth muscles)– Body cavity

• Coelom is reduced; • Most of body cavity consisting of

hemocoel (sinuses, or spaces, in the tissues) filled with blood;

– Digestion • Complete digestive system

– Esophagus, crop, gizzard, midgut, hindgut and anus

• mouthparts modified from appendages and adapted for different methods of feeding;

– Circulatory System• Open system• dorsal contractile heart, arteries

– Respiration• Obtain oxygen through body surface

(diffusion), gills, tracheal (air tubes), or book lungs; – Tracheal tubes—carry oxygen to the muscles

• Spiracles—small openings in the exoskeleton through which air opens

– Water retention—3 structures that aid• Malpighian tubules—excretory structures

that remove metabolic wastes from blood and return water to the cells

• Exoskeleton—prevents water evaporation• Book Lungs—gas exchange without water

loss (also used in respiration)

– Excretory system• Paired excretory glands in some • homologous to nephridial system of annelids; • some with other excretory organs, called Malpighian tubules;

– Nervous system• Contains same system of annelid (with dorsal brain connected

by a double nerve chain of ventral ganglia); • fusion of ganglia in some species; • well-developed sensory organs;

– Compounds eyes with many lenses (can see motion and color)

– Reproduction• Sexes usually separate, • paired reproductive organs and ducts; • usually internal fertilization; often with metamorphosis;