Arthropods Chapter 28

What is an Arthropod? Characteristics: Invertebrate animals with bilateral symmetry A coelom Exoskeleton Joint appendages

Appendages Are anything like legs, antenna that grows out of the body Are adapted for sensing, walking, feeding & mating Arthropods were 1 st to evolve jointed appendages

Appendages Allows for more powerful movements Different uses ex: spiders use their 2nd pair of appendages for sensing & mating Ex: scorpions seize their prey

Purpose of exoskeleton Gives protection Supports internal tissue-gives muscles place to attach Some covers entire body-some animals held together by hinges Made of Chitin

Disadvantages of Exoskeleton Relatively heavy structure (Jump & Fly) Cannot grow so they shed periodically- molting Most molt 4-7 times during their life Most vulnerable to predators

Steps Associated with Molting 1. A new one develops beneath the old one 2. The muscles contract in the rear part of the body, forcing blood forward causing this part of the body to swell & split 3. The animal wiggles out

Spider Molting

Body segments of Arthropods Segments have fused into 1 – 3 body sections 1. Head 2. Thorax 3. Abdomen

Body segments of Arthropods Other groups have 2 body segments 1. Fused head & thorax called a cephalothorax 2. abdomen

Movement Generally quick, & active Can crawl, run, climb, dig, swim & fly Flies beat their wings 1000 times/sec

3 types of Gas Exchange (Air) 1. Gills aquatic arthropods (lobster, crayfish, crab…) exchange gas through gills

3 types of Gas Exchange (Air) 2. Tracheal Tubes Most insects have tracheal tubes- branching network of hollow air passages

3 types of Gas Exchange (Air) 3. Book lungs Most spiders have book lungs – air filled chambers that contain leaf-like plates that look like pages of a book

Acute Senses Movement, sound & chemicals are detected with an antennae Antennae also aid in communication

Antenna Ants work together because they communicate with a pheromone-which is a chemical odor signal given off by the animal and detected with the antenna

A Bugs Life…Wonderful Example

Vision is important Most arthropods have 1 pair of large compound eyes (visual structures with many lens) Or 3-8 simple eyes (visual structure with 1 lens) Total images make up thousands of parts (dots like a t.v. screen)

Nervous System Well-developed that can process information coming in from the sense organ Most excrete waste through Malpighian Tubes

Other complex body systems Mouth parts include a variety of jaws called mandibles adapted for holding, chewing, sucking or biting different foods

Other information 1. Have separate male & female species 2. Reproduce sexually -fertilization occurs internally in land species -externally in aquatic species 3. Blood is pumped by 1 or more hearts to an open circulatory system 4. Have complete circulatory system, & digestive system

Beneficial to Humans 1. Pollinate many flowering plants & crop plants 2. Provide food, honey, shellac, wax & silk 3. Provide alternative chemical control of insects 4. Research has advanced in the fields of genetics, evolution, and biochemistry -Crab shells make artificial skin, surgical sutures & antifungal medicines

Problems for Humans 1. Insects eat important crops (bole weevil) 2. Spread plant and animal disease (malaria & yellow fever) 3. Costly for us…

Crustaceans

Crustaceans: Mostly are aquatic Have mandibles for crushing food 2 pairs of compound eyes 2 pairs of compound eyes which are on moveable stalks 5 pairs of walking legs used to seize prey & clean appendages Characteristics:

The first pair of walking legs are often modified into strong claws for defense.

Shrimp Members of Crustaceans Barnacles Crab

A Few Land Crustacean Pill Bug & Sow Bug, two of the few land crustaceans, must live where there is moisture, which aids in gas exchange Pill Bug Sow Bug

Horseshoe Crab Horseshoe crabs are considered to be living fossils & have remained relatively unchanged since the Triassic Period They forage on sandy or muddy ocean bottoms for algae, annelids, and mollusks

Insects: class Insecta Insects have three body segments and six legs There are more species of insects than all other classes of animals combined. Only group of animal that has never lost an individual to extinction

Centipedes Centipedes are carnivorous and eat soil arthropods, snails, slugs, and worms The bites of some centipedes are painful to humans.

Millipedes A millipede eats mostly plants and dead material on damp forest floors. Millipedes do not bite, but they can spray foul- smelling fluids from their defensive stink glands.

Leaf Cutter Ants

Other Members… Lice, Grasshoppers, flies, butterflies, bees & beetles….

Insect Reproduction Most insects lay a large number of eggs, which increase the chances that some offspring will survive long enough to reproduce. The insect embryo develops and the eggs hatch

Metamorphosis: change in body shape and form This series of changes, controlled by chemical-substances in the animal 2 types of metamorphosis 1. Complete Metamorphosis 2. Incomplete Metamorphosis

Complete Metamorphosis Complete metamorphosis consist of four stages on their way to adulthood: Egg  Larva  Pupa  Adult.

Incomplete Metamorphosis Incomplete metamorphosis consist of three stages on their way to adulthood Egg  Nymph  Adult

Arachnids Spiders, Scorpions, Mites & Ticks

Arachnids 30,000 species of spiders – only 12 native to North America Cannot chew food- use digestive enzyme to liquefy food Crab Spider

Ticks & Mites Differ from spiders because they only have one body segment

scorpions Scorpions are easily recognized by their body segments & enlarged pinchers They have a long tail with a venomous stinger at the tip.

Arachnids known for webs Silk is made from silk glands & is spun into thread by spinnerets located at the rear of the spider Link for spider webs

Spider spinning an insect

Venomous Spiders… Black Widow web used in WWI for cross-hairs in riffles Brown Recluse

Spiders 1 st pair of appendages called chelicera (located near mouth, modified pinchers/fangs) used to hold food 2 nd pair called pedipalas handle food & sensing Banana Spider