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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
» Body organization: head, thorax, and
• 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
• 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
• Spiracles—small openings in the
exoskeleton through which air opens
– Water retention—3 structures that
• Malpighian tubules—excretory
structures that remove metabolic wastes
from blood and return water to the cells
• Exoskeleton—prevents water
• 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
– 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;