Arthropods

Chapter 28

Arthropods

• Have a segmented body.• A tough exoskeleton.

• Jointed appendages that extend from the body wall.

• Environments they occupy are:– Sea, land, and air.The evolution of arthropods, by natural selection &

other processes, has led to fewer body segments & highly specialized appendages for feeding, movement, & other functions.

Arthropods

• Have a digestive tract, an open circulatory system, and an exoskeleton.

• Insects has a network of tracheal tubes where gas exchange takes place.

Arthropods

• Molting – arthropods outgrow their exoskeletons and will shed the entire thing and replace it with a new larger one.

• Arthropods are classified based on the number and structure of their body segments and appendages.

Arthropods

• Groups of Arthropods are:– Crustaceans – crab, shrimp, lobster, crayfish &

barnacles.– Spiders – spiders, ticks, scorpions & horseshoe

crabs.– Insects – centipedes, millipedes & insects.The easiest way to tell whether an arthropod is

an insect or a spider is to count its legs. Spider has 8, insects have 6.

Arthropods

• Insects – reason for evolutionary success is:– Ability to fly allows insects to colonize new habitats.– They may use many sense organs to respond to

stimuli.– Many have a life cycle in which the young are very

different from adults.– The body is divided into a head, thorax, and

abdomen.– Sensory hairs – insects use these hairs along with its

compound eyes to detect minute movements in its environment

Arthropods

• Difference between a Nymph and a Larva:– A nymph resembles an adult of the same

species, but a larva do not.

Echinoderms

• Spiny skin.

• Internal skeleton.

• Water vascular system.

• Suctioncuplike structures called tube feet.

• Radial symmetry.

• Examples – sea stars, sea urchins, sand dollars.

Comparing Invertebrates

• Digestion- intracellular or extracellular.

• Respiration- gills, book lungs, or tracheal tubes.

• Circulation– Open circulatory system blood is pumped through a

system of sinuses. One or more hearts.– Closed circulatory system blood is contained within

vessels that extend throughout the body. • Response (nervous system)-senses gather & process information.

• Excretion- eliminating nitrogenous wastes from the body.

• Movement & support• Reproduction- asexual & sexual

Chordates

Characteristics • A dorsal, hollow nerve cord• A notocord.• A pharyngeal pouches.• A tail that extends beyond the anus.• A vertebrate is any chordate that has a

backbone so any animal with a spinal cord must be a vertebrate.

Fish & Amphibians

FISH • Aquatic vertebrate.• Most have paired fins, scales, and gills.• Gills –structures that are important for obtaining oxygen from

water.• Heart has one atrium.

AMPHIBIANS• Lives in water as a larva & on land as an adult.• Adult breathes with lungs.• Moist skin, no scales and claws.• Example – frogs, toads, & salamanders

Reptiles & Birds

REPTILES• Dry, scaly skin.

• Lungs.

• Terrestrial eggs with several membranes.

• Can live their entire life outside of water.

• Groups–lizards, snakes, crocodiles, &turtles

• They do not excrete ammonia like most Chordates.

• Snakes are reptiles with no legs and skin unlike other reptiles.

Reptiles & Birds

BIRDS• Maintain a constant internal body temperature.• Outer covering is feathers.• Two legs that are covered with scales and are used for

walking, perching.• Front limbs are modified into wings.

• Not all birds can fly.• To distinguish bird eggs from reptile eggs, you must

test the hardness of the outer shell.• A bird’s heart ensures that oxygen-rich blood never

mixes with oxygen poor blood.

Mammals

• Have hair.

• Have the ability to nourish their young with milk. Mammary glands – found only in female mammals

• Breathe air.

• Have a 4- chambered heart and system that carries oxygen-rich blood directly from the heart to the muscles.

• Are endotherms that generate their own body heat internally.

• Water in the body is controlled by the kidneys.

Mammals

3 Main Groups of Mammals

• Monotremes – lay eggs. Ex. Platypus, anteaters.

• Marsupials – bear live young, but at a very early stage of development. Ex. Kangaroo, Koalas, Wombats

• Placental mammals – have a placenta which exchanges materials between an embryo and its mother. Ex. Mice, cats, dogs, whales, humans