Arthropods

Phylum Arthropoda - Arthropods

Largest and most successful phylum

75% of all animals! Segmented body Tough exoskeleton Joint appendages (legs and

antennae) Cephalization Bilateral Symmetry

Exoskeleton: an external covering that protects and supports the body– Made from chitin– Varies in size, shape, and roughness.

Firm and leathery (caterpillars)Tough and hard (crabs and lobsters)Waxy (land dwelling arthropods)

Evolution of Arthropods

Evolution of Arthropods

Typical primitive arthropod:

– many identical segments with a pair of appendages.

Evolution led to fewer segments and specialized appendages

Fossilized Trilobites

Feeding

Feeding– Includes herbivores, carnivores,

omnivores, detritivores, filter feeders, bloodsuckers, and parasites.

– Mouth parts adapted to type of food eaten

Pincers, fangs, jaws

• Terrestrial arthropods: breathe through tracheal tubes

• Air enters and leaves tracheal tubes through spiracles

• small openings located along the side of the body.

Tracheal tubes

Tracheal tubes

Spiracles

RESPIRATION

• Book lungs organs that have layers of respiratory tissue (stacked like pages of a book.) • Spiders, scorpions,

horseshoe crabs

RESPIRATION CONTINUED…

Circulation and Excretion

Arthropods have a open circulatory systemNo distinction between blood and other

fluids

Malpighian tubules (terrestrial): saclike organs that extract waste from the blood

Diffusion (aquatic)

Response and Reproduction

Response– Well developed nervous system– Brain serves as central switchboard

Reproduction– Terrestrial arthropods: internal fertilization

Place sperm inside female OR deposit sperm packet– Aquatic arthropods: internal or external

Reproduction

Separate sexessexual reproduction Males directly transfer sperm to

females Ex. Barnacle stretches out

appendage to local females Mating occurs after female molts

Movement: Groups of well developed muscles coordinate movement – generating force by pulling on the exoskeleton– Muscles flex (bend) or extend (straighten) the

joint.

MOVEMENT

Growth and Development

Arthropods will outgrow their exoskeleton and undergo a period called molting.

Molting: the shedding of its entire exoskeleton – New/soft skeleton starting to form– Controlled by the endocrine system– Molting Cicada Video – http

://upload.wikimedia.org/wikipedia/commons/6/62/Cicada_molting_animated-2.gif

Groups of Arthropods

Classified by number of body segments and mouth parts

3 major groups1. Crustaceans 2. Spiders and their relatives3. Insects and their relatives

1) Crustaceans Primarily aquatic

– Includes crabs, shrimps, lobsters, crayfishes, and barnacles.

– 2 pairs of antennae, two or three body sections, and chewing mouthparts called mandibles.

Cephalothorax

Abdomen

Mandible

Antennae

Antennules

Body Plan of Crustaceans

Cephalothorax– Fusion of head with

the thorax Mandible:

– Mouthpart adapted for biting and grinding food

swimmerets

Cheliped

• Cheliped: first pair of legs that have large claws modified to catch, pick up, crush, and cut food.

• Swimmerets: flipper-like appendages used for swimming

1) Small Crustaceans

Copepods- extremely abundant, planktonic, filter feed

Barnacles- usually sessile, filter feed, body enclosed by calcareous plates

Krill- planktonic, shrimp-like, have carapace to cover anterior, filter feed

True Crabs

Small abdomen and tucked under cephalothorax

V-shape ab. in males U-shape ab. in females Largest and most diverse of

decapods Scavengers and predators

Male Jonah Crab

Female Jonah Crab

2) Chelicerates Horseshoe crabs, spiders, ticks, and

scorpions– No antennae– Have mouthparts called chelicerae– 2 body sections– 4 pairs of walking legs

Divided into 2 main classes: Merostomata (horseshoe crabs)Arachnida (spiders, mites, ticks, and

scorpions)

Horseshoe crabs

Horseshoe Crabs Appeared more than 500 million years ago

– changed little since that time. Have chelicerae, five pairs of walking legs,

and a long spike-like tail (telson) that is used for movement.

Horseshoe Crab

1. Carapace 2. Telson 3. Compound eye 4. Anterior spine Five pair of legs

Spiders

Food and Digestion– Spin webs of a strong, flexible protein

called silk– No jaws for chewing

must liquefy food using enzymes Use fanglike chelicerae to inject paralyzing

venom

What does the spider use silk for?

Silk glandsSpinnerets

Mites, Ticks, and Scorpions

Mites and ticks are small arachnids that are often parasitic

Ticks can transmit bacteria that cause serious diseases– chelicerae and pedipalps are specialized for

digging into a host’s tissues and sucking out blood

Scorpions inhabit warm areas around the world.– Chew their prey

3) Uniramians

Centipedes, millipedes, and insects Characteristics of Uniramians

– Have jaws– One pair of antennae– Un-branched appendages– Carnivores

Class Insecta (Insects)

Characteristics of Class Insecta– Contains most species of any other

animals– Body divided into 3 segments

Head, thorax, and abdomen

Characteristics continued…

Segmented body Exoskeleton Jointed appendages A typical insect also has:

a pair of antennae a pair of compound eyes two pairs of wings on the thorax tracheal tubes that are used for respiration

Response

Compound Eye: made up of many lenses – Detect minute changes in color and movement – Information from eye is assembled in the brain

and directs the insects response Chemical receptors for taste and smell

– Located on the mouthparts, antennae, and legs Sensory hairs: detect movement in

surrounding air or water Well developed ears

Feeding and Specialized Mouth Parts

3 pairs of appendages that are used as mouthparts, including a pair of mandibles

Mandibles used to saw and grind food

Ant

Specialized mouth parts continued…

Spongelike mouthpart used to lap up food

Fly

Specialized Mouth Parts

Tubelike mouthpart used to suck nectar

Moth

Movement and Flight

3 pairs of legs used for walking, jumping, capturing and holding prey.– Legs have spines and hooks that are

used for grasping and defense. Flying insects typically have two

pairs of wings made of chitin

Metamorphosis

Process of changing shape and form– Insects undergo either incomplete

metamorphosis or complete metamorphosis

Incomplete Metamorphosis– Look very much like adult form– Immature forms are called nymphs

lack functional sexual organs and wings

Complete Metamorphosis

Animals hatch into larvae that look and act nothing like their parents

Feed and grow rapidly and molt a few times

Undergo a final molt and change into a pupa– stage in which an insect changes from

larva to adult.