1. Arthropods!
Ch 28 Presentation

2. Common Characteristics of all Arthropods
Typical arthropod:
Segmented
Coelomate with Bilateral symmetry
Invertebrate with exoskeleton
Jointed structures called appendages
Appendage—any structure (e.g. leg, antenna) that grows out of the body of an animal
In arthropods, appendages are adapted for walking, sensing, feeding, mating, etc.
Arthropods are earliest known invertebrates to exhibit jointed appendages
Joints allow for flexibility of rigid exoskeleton (think knight in suit of armor)
Joints enable many uses for various appendages (e.g. mating in spiders, stinging in scorpions)

3. Exoskeletons Support and Protect
Exoskeleton—hard, thick outer covering of protein and chitin
In some species, exoskeleton is continuous over entire body, in others it is separate plates held together by hinges
Exoskeleton supports internal tissues, provides places for muscle attachment
In many terrestrial species, exoskeleton covered with waxy layer to minimize water loss
In many aquatic species, exoskeleton reinforced with calcium carbonate

4. Oh no, it’s MOLTING! Why molt?
Exoskeletons are heavy and thick (the larger the muscles, the heavier/thicker must the exoskeleton be), so weight is limited for arthropods
Terrestrial and flying arthropods have thinner, lighter (but more fragile) exoskeletons but are less protected
Molting—shedding the old exoskeleton (new soft skeleton formed underneath first)
Animal takes in air/water and contracts muscles, which swell and split old skeleton
Most arthropods molt 4-7x during lifetime before becoming adults
Mid-molt, animals are vulnerable to predators, so many hide or remain motionless until their new skeleton hardens

5. Segmentation
Most arthropods are segmented but do not have as many segments as worms
In most groups, segments fused into three zones:
Head, thorax, abdomen
Sometimes head and thorax
fused together into
cephalothorax

6. Breathing
Arthropods have efficient gas exchange—generally quick, active animals with high oxygen requirements
Three types of respiratory structures:
Gills
Tracheal tubes
Book lungs
In some arthropods, gas exchange occurs across exoskeleton (so it must be thin and permeable)
Aquatic arthropods use gills
Land arthropods use either tracheal tubes or book lungs
Most insects use tracheal tubes (branching networks of hollow air passages that carry air throughout body)
Air enters and leaves body through openings on thorax and abdomen called spiracles
Spiders and their relatives use book lungs, air-filled chambers with leaf-like plates (maximize surface area for gas exchange)

7. Tracheal Tubes and Spiracles
Book Lungs
Book Lungs

8. Acute Sensory Perception
Why can arthropods respond so quickly to their environment?
Strong muscular contraction
Detect movement, chemicals and sound with antennae
Antennae have odor and sound receptors that are used in communication with other members of species (spiders lack these)
Pheromones—chemical odor signals given off by animals (signal animals to engage in variety of behaviors)
Accurate vision: EYES
Most arthropods have one pair of large compound eyes and 3-8 simple eyes
Simple eyes- single lensed-structures for detecting light
Compound eyes—visual structures with many lenses
Each lens registers a tiny portion of the field of view, so the total image is made of thousands of parts (panoramic view)

9. What structures allow this damselfly to sense its environment?
Eyes
What structures allow this damselfly to sense its environment?

10. Well-developed Nervous Systems
Arthropods process information from sense organs with well-developed nervous systems
Consists of double ventral nerve cord (pearl necklace), an anterior brain, and several ganglia

11. Arthropod Circulation
Open circulatory system—blood is pumped by a heart, through vessels that bathe the tissues of the body, returns to heart through open spaces

12. Complex Digestive Systems
Mouth, stomach, intestine, anus, glands that produce digestive enzymes

13. Diversity of Mouthparts
Mouthparts are grouped and adapted for a vast variety of foods eaten by arthropods
Mandibles for chewing, pinching, holding
Pairs of appendages for moving food around while chewing
Some insects have blade- or needle-like mouthparts for piercing for drawing blood, etc., while others have sponging tongues to lap up food, rolled-up proboscises for sucking up food

14. Insect Mouthparts
Most mouthparts of arthropods include one pair of mandibles (green)
These are adapted for holding, chewing, or biting various foods
Labrum: upper-most mouthpart (red)
fused plate to hold food in place during chewing
Maxillae (yellow): hold and manipulate food during mastication
Hairs and “teeth” along inner ridge
Palps used for sensing the characteristics of potential foods
Modified into proboscis or straw-like tube for sucking up food
Labium: “floor” of the mouth, assists during chewing (blue)
Hypopharynx: base of labium, assists in swallowing

15. Crustacean Mouthparts
Three pairs of appendages modified into mouthparts that manipulate and bring food into mouth (mandibles followed by two pairs of maxillae)
Paired appendages offer opposable surfaces for grinding and biting food
Often followed by setae used to collect food

16. Arachnid Mouthparts
Spiders and scorpions have chelicerae—pointed appendages used to grasp food
In spiders, they are hollow and contain venom glands

17. Other well-developed systems
Excretory: Malpighian tubules that remove waste from abdomen; attached to and empty into the intestine
Muscular: muscle is attached to inner surface of exoskeleton on both sides of joints

18. Sexual Reproduction
Most arthropods have separate males and females and reproduce sexually
Fertilization usually internal, sometimes external in aquatic species
A few species hermaphroditic
Barnacles
Parthenogenesis—asexual reproduction in which new individual develops from unfertilized egg (ex. Bees, wasps, ants, aphids; males with only one X chromosome)
Reproductive diversity one reason why more arthropod species than ALL the other animal species combined

19. Arthropod Diversity Arachnidae: Spiders, scorpions, mites, and ticks
Spiders have two body sections: cephalothorax, abdomen
Six pairs of jointed appendages
Chelicerae: first pair of appendages located near the mouth
Modified into pincers or fangs, spiders have no mandibles for chewing
Pedipalps: second pair, adapted for handling food and sensing food
Arachnids have no antennae
Spiders can make elaborate webs– though all spiders spin silk, not all make webs
Silk secreted in glands in abdomen, then spun together into thread by spinnerets located at rear of spider
Ticks, mites, scorpions: only one body section (head, thorax, and abdomen completely fused
Mites feed on fungi, plants, animals
Small but can expand body size up to 3x original size
Scorpions have long tail with venomous stinger at tip, enlarged pincers

20. Arthropod Diversity
Crustacea: body sections, two pairs of antennae for sensing, two compound eyes, mandibles for crushing food (ex. Shrimp, lobsters, crabs, barnacles, crawdads
Crustacean mandibles open and close side to side
Many have five pairs of walking legs
Used for walking, seizing prey, cleaning appendages
First pair of walking legs often modified into strong claws for defense

21. Arthropod Diversity Chilopoda: centipedes, Diplopoda: millipedes
Have Malpighian tubules for excreting wastes
Tracheal tubules for gas exchange
Centipedes are carnivorous with painful bites
May have body segments, each with one pair of legs
Millipedes don’t bite, eat mostly plants and dead material on forest floors
Spray foul-smelling fluid from stink glands as defense
May have 20 to 100+ segments, with two spiracles and legs each

22. Arthropod Diversity Merostomata: Horseshoe crabs—”living fossils”
Three living genera, one (Limulus) lives along North American East Coast, two live in Asian tropics
Limulus fossils unchanged since Triassic Period 220 mya
Heavily protected by extensive exoskeleton; live in deep coastal waters; forage for algae, annelids, mollusks
Migrate to shallow water in spring, mate at night during high tide

23. Arthropod Diversity Insecta: the most successful class of arthropods
3 body segments, six legs, more species of insects than all other animals combined
Reproduction: usually once during lifetime, internal fertilization
Parthenogenesis: in aphids all female offspring; in bees/ants/wasps all male
Most lay large # of eggs, increases chances of offspring survival to reproductive maturity

24. Metamorphosis
Metamorphosis—change in body shape from egg to adult, controlled by series of chemical changes in animal
EggLarvaPupaAdult
If insect goes through all four stages: complete
If insect goes through some stages: incomplete (nymph stage)
Complete metamorphosis advantageous for arthropods because larvae don’t compete with adults for the same food

25. Origins of Arthropods
Successfully covered the whole surface of Earth more than any other group of animals because of their ability to survive in almost every habitat
Exoskeletons, life cycles, high reproductive output, small size, jointed appendages
Most likely evolved from annelid ancestor
Evolved fused body segments that adapted for movement, sensing environment
More complex than annelids (eyes, nervous tissue)
Trilobites were major group of ancient arthropods, but have been extinct 248 million years