Arthropods Chapter 28

Arthropod characteristics Segmented bodies Tough exoskeleton made of chitin Multiple shapes and textures Jointed appendages: legs and antennae

Arthropod evolution Modern arthropods have fewer body segments and more specialized appendages. Fossil of a Trilobite, extinct class of Arthropod

Fossil of Leanchoilia, Phylum Arthopoda www.burgess-shale.bc.ca/ gallery/gallery.htm

Feeding Herbivores, carnivores, omnivores, parasites, blood suckers, filter feeders, and detritovores Variety of mouthparts: pincers, fangs, sickle-shaped jaws, feeding tubes stag beetle pincers

Respiration Most arthropods Some arthropods (including spiders) Tracheal tubes: branching network of tubes that deliver and expel air through spiracles Some arthropods (including spiders) Book lungs: layers of respiratory tissue stacked like pages of a book

Circulation Open circulatory system: heart pumps blood to tissues, sinuses, and cavities but does not return to the heart directly

Excretion Malpighian tubules: saclike organs that extract wastes from blood and then add them to feces to move through the gut

Chrysina quetzalcoatli is freed in Cusuco National Park, leaving a fecal trail National Geographic

Response Sensitive sensory organs (sight, smell, touch) Well-developed nervous system Brain Ventral nerve cord Ganglia: groups of nerve cells

Movement Flexor muscles Extensor muscles Muscle pulling against exoskeleton enables movement

Reproduction Terrestrial arthropods: internal fertilization Male places sperm in female Sperm sac that female picks up Aquatic arthropods: internal or external fertilization

Growth and development Molting: period of shedding exoskeleton when outgrown Glands secrete digestive enzymes to break down exoskeleton. Glands secrete new exoskeleton. Vulnerable stage Insect molting case left on tree bark

Arthropod subphylums Crustaceans Spiders and their relatives Insects and their relatives

Crustacean characteristics Two pairs of antennae Two or three body sections Mandibles: chewing mouthparts Body plan: celphalothorax, abdomen, carapace Barnacles have “lost” appendages. Decapods have chelipeds and swimmerets. Ex: shrimp, lobster, crayfish

The Anatomy of a Crayfish Section 28-2 Abdomen Tail Swimmerets Carapace Cheliped Mandible Second antenna First antenna Cephalothorax Walking legs

Subphylum Crustacea – hermit crab

Subphylum Crustacea –crab

Subphylum Crustacea – fire shrimp

Chelicerate characteristics Four pairs of walking legs Chelicerae mouthparts: fangs that sting and pedipalps that grab prey Two body sections: cephalothorax and abdomen Classes: Merostomata (horseshoe crabs) and Arachnida (spiders, scorpions) Spiders have spinnerets, silk glands.

The Anatomy of a Spider Figure 28–9 Section 28-2 Cephalothorax Abdomen Eyes Brain Pumping stomach Heart Intestine Ovary Malpighian tubules Anus Spinnerets Silk glands Spiracle Bases of walking legs Fanglike chelicera Pedipalp Poison gland Airflow Book Lung Figure 28–9 

Subphylum Arachnida – black widow spider

Scorpion

Gum shoe spider web Theridae family National Geographic Photo by Darlyne A. Murawski

Uniramia characteristics Jaws One pair of antennae Unbranched appendages Groups: centipedes, millipedes, insects

Millipede

Centipede

Why insects are evolutionarily successful Flight Variety of stimuli responses Differential feeding methods between young and adult Different morphology between young and adult

Insect characteristics Compound eyes Some with wings Three part body plan Three pairs of legs Sensitive taste and smell receptors Three appendages for mouth, including pair of mandibles

The Anatomy of a Grasshopper Section 28-1 Antennae Compound eye Brain Digestive tract Malpighian tubules Heart Reproductive organs Anus Spiracles Tracheal tubes Nerve cord Ganglia Salivary glands Mouth Ventral View Legs Tracheal tubes Spiracles Figure 28–4 

Insect life cycle Metamorphosis: process of changing shape and form from juvenile to adult stage Incomplete: juvenile stage (nymphs) appear like adults, just smaller Complete: juvenile stage (larvae) becomes pupa, final stage before becoming an adult

Incomplete Metamorphosis Complete Metamorphosis Section 28-3 Adult Adult Eggs Eggs Incomplete Metamorphosis Complete Metamorphosis Larva Adult Nymph Nymph Immature Larva Nymph Adult Pupa Figure 28–18 

Insects and humans Although they can be a nuisance or pest, insects are significant to agriculture. They facilitate flower pollination.

Insect communication and societies Chemical cues: pheromones Visual cues: light, flight patterns Some insects form societies where castes, groups of individuals, perform specific tasks.

Polyphemus moth Pheromone chemical: (E,Z)-6,11-Hexadecadienyl acetate National Geographic Image  by Joseph Scheer

Subphylum Insecta – lady bug

Subphylum Insecta – bee moth