Chapter 26 Arthropods Joint limbed arthropods (1 min)

Arthropod Characteristics Segmented Coelomates Invertebrate Bilateral symmetry Exoskeleton (chitin) Jointed appendages – which allow for more flexibility

Arthropod Senses Antennae - detects movement, sound, and chemicals Pheromones – communication chemicals May have 2 compound eyes and 3 to 8 simple eyes Simple eyes w/ one lens used to detect light Compound eyes w/ many lenses used to detect movement and color

Arthropod Body Systems Well developed nervous system Open circulatory systems w/ one or more hearts Complete digestive system w/ mouth, stomach, intestine, and anus

Other Systems Malpighian tubules remove waste Good muscular system attached to the inside of the exoskeleton Most reproduce sexually Internal fertilization (on land) External fertilization (in water)

Parthenogenesis Parthenogenesis - when an adult forms from an unfertilized egg (asexual reproduction) In social insects (honeybees & ants) unfertilized eggs (haploid) develop into the male drones fertilized eggs (diploid) develop into the female workers and queens. Used to increase reproduction rates.

Arthropod Molting Exoskeletons are heavy and cannot grow Arthropods molt (shed their exoskeleton) in order to grow. Most molt 4 – 7 times They are very vulnerable during this time

Arthropod Segmentation Most have three body sections: The head, thorax, and abdomen Some have two body sections: an abdomen and a cephalothorax (fused head and thorax)

Gas Exchange Three types of respiratory structures: Gills – found in aquatic species Tracheal tubes – found in insects Hollow air passageways Spiracles are openings that allows air to enter or leave Book lungs – found in spiders Air-filled chambers with leaflike plates Some diffuse air directly through the body

Diversity of Arthropods Six classes of arthropods. Arachnida, Crustacea, Chilopoda, Diplopoda, Merostomata, and Insecta Amazing Arthropods (13 min)

Class: Arachnida Examples: Spiders, scorpions, mites, & ticks North America has only two species of spiders dangerous to people Arachnids are found throughout the world in nearly every habitat, but they reach their greatest size and diversity in warm arid and tropical regions 6 pairs of jointed appendages

Arachnid Characteristics The body is divided into two parts The anterior part, the cephalothorax Has sense organs, mouthparts, and limbs in pairs They do not have antenna The first pair of limbs, the chelicerae, may form pincers or poison fangs the second pair, the pedipalps, may serve as pincers, feelers, legs, hold reproductive parts The other limb pairs, generally four, are used for walking. The posterior part of the body, the abdomen Has the genital opening Has book lungs Solitary except at the time of mating, when a variety of complex behavior patterns may be observed. Females may guard eggs or young, which are often born live.

                                                                                                                                         

Arachnida Spiders use extracellular digestion All spiders spin silk, but not all make webs Spinnerets are used to spin silk Ticks and mites have a single fused body section Scorpions have many abdominal segments, large pincers, and a venomous stinger on their tail

Spider Silk Spider's silk is made up of chains of amino acids (protein). Spider silk is extremely strong -- it is about five times stronger than steel and twice as strong as Kevlar of the same weight. Spider silk also has the ability to stretch about 30-percent longer than its original length without breaking, which makes it very resilient.

Spider Silk Goats are being genetically altered to produce ‘spider silk’ in their milk. A thread of silk the diameter of a pencil could lift a 747 After a few days the web dries out and is no longer sticky. The spider eats and recycles the old web.

Normal 5x 20x

Spinnerets

Shown here is a close-up view of the pedipalps of a mature male Grammastola rosea (Chilean rose hair tarantula).                                                                                           

Flower spider

Black Widow Spider (26 min)

Crustaceans Most crustaceans are aquatic and have gills 2 pairs antennae All have 2 compound eyes, usually on moveable stalks Mandibles open sideways Some have 5 pairs of walking legs Pill bugs are the only land crustaceans

Examples of Crustaceans Crabs Crustacean Video (3 min) Lobsters Shrimp Crayfish Barnacles Barnacles (18 sec) Water fleas (Daphnia) Pillbugs

Centipedes and Millipedes Centipedes - class Chilopoda Millipedes - class Diplopoda

Centipedes Centipedes are carnivorous and have a painful bite using fangs Centipedes have an odd number (15-181) of body segments One pair of legs per segment Generally flattened Have a pair of well developed antennae on the head

Millipedes Millipedes eat mostly plants They don’t bite, but they can release a foul smelling fluid Millipedes can have 100+ segments, each with 4 legs and two spiracles Millipedes have more rounded bodies

South American Centipede Video (1 min)

Class: Merostomata Horseshoe crabs are almost the same now as they were 500 million years ago during the Cambrian period and are called living fossils They have a very effective exoskeleton

Horseshoe Crabs The horseshoe crab has survived because it can go a year without eating and endure extreme temperatures and salinity A horseshoe crab's tail, while menacing, is not a weapon. Instead, the tail is used to plow the crab through the sand and muck, to act as a rudder, and to right the crab when it accidentally tips over.

Horseshoe Crab Video (11 min)

Class Insecta The largest class of arthropods! Insects usually mate only once or they might mate only a few times during their lifetime They lay many eggs at once Eggs are fertilized internally Insecta is the most successful and diverse class of organisms on earth

Class Insecta Have 3 body segments Have 3 pairs of legs Have 1 pair of antenna Many fly Amazing World of Insects (26 min)

Metamorphosis Many insects undergo metamorphosis from egg to adult Complete Metamorphosis – egg, larva, pupa, and adult Larva is wormlike and are called caterpillars The pupa stage is a major change in body systems Examples include butterflies, ants, wasps, beetles, etc.

Metamorphosis Incomplete Metamorphosis – is a gradual change with three stages Egg, nymph, and adult Nymphs look like tiny adults Examples are cockroaches and grasshoppers

Insect Metamorphosis (21 min)

Insect Fact and Folklore (22 min)