ARTHROPODS Four subphyla trilobites: ancient seas; extinct chelicerates: spiders, ticks, mites, scorpions, & horseshoe crabs crustaceans: crabs, shrimp, & lobster uniramians: centipedes, millipedes, & all insects Form and Function: Three most important features: tough exoskeleton chitin- makes up the exoskeleton some hard and brittle, others leathery and flexible waterproof- restricts water loss advantages and disadvantages????? jointed appendages antennae, claws, walking legs, wings, flippers and others segmented body plan some with many-millipede; others with few-crayfish

ARTHROPODS Feeding Respiration Internal Transport Mouth parts designed for different diets plants, meat, drink blood, flowers, filter feeders Respiration Three structures for respiration gills: aquatic; crayfish, lobster, shrimp book lungs: aquatic & land; horseshoe crabs, spiders spiracles- openings connecting the air sacs with the outside air tracheal tubes: land; insects, some spiders, millipedes; fig. 28-8; From spiracles long branching tracheal tubes reach into the animals body tissues. The mov’t of body muscles causes the air to move in and out of the spiracles. Internal Transport Heart pumps blood through an open circulatory system contains sinuses- spaces in the tissue in which blood can move

ARTHROPODS Excretion Solid wastes leave through the anus Nitrogen-containing wastes from metabolism varies terrestrial arthropods use a set of Malpighian tubules tubes bathed in blood remove the wastes from blood, concentrate them and add them to undigested food, then out the anus some have excretory glands at the bases of their legs as well aquatic: diffuses from the body into the surrounding water at unarmored places like the gills. Others, like the lobster, use a pair of green glands near the base of the antennae. Response Brain with a pair of ganglia in the head. A nerve cord runs down the body parts with branching ganglia along the way. Cut off head; still flaps wings

ARTHROPODS Response compounds eyes 2000 separate lenses detecting color and mov’t taste receptors on mouth, legs, and antennae ear drums detecting sound above the human range; some on legs These are all key for protection along with venomous stings & bites Movement well developed muscles coordinated by a nervous system (fig. 28-13) Reproduction usually internal spiders and some crustaceans deposit sperm packets, which are picked up by the female. GROWTH AND DEVELOPMENT IN ARTHROPODS molting- the shedding of the exoskeleton The epidermis digests the inner part of the exoskeleton and absorbs much of the chitin. It secretes a new exoskeleton inside the old one.

ARTHROPODS Metamorphosis (fig. 28-15) Incomplete has three stages egg; nymph; adult Complete has four stages egg; larva, pupa, adult larva- caterpillar pupa- cocoons insects body is totally rearranged Controlled by a complicated interaction of hormones The amount of juvenile hormone keeps the insects at the larval stage and molting for quite a time. As the level decreases it goes into the pupa stage. Insecticides are used to control the pests because the insecticides affect the balance of the hormones.