Arthropods

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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

Fossilized Trilobites

 Evolution of Arthropods  Typical primitive arthropod: – many identical segments with a pair of appendages.

 Evolution led to fewer segments and specialized appendages

Feeding

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Feeding

– Includes herbivores, carnivores, omnivores, detritivores, filter feeders, bloodsuckers, and parasites.

– Mouth parts adapted to type of food eaten  Pincers, fangs, jaws

RESPIRATION

• 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 Spiracles Tracheal tubes

RESPIRATION CONTINUED…

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

Circulation and Excretion

 Arthropods have a open circulatory system No distinction between blood and other fluids   Malpighian tubules organs that extract waste from the blood (terrestrial): saclike Diffusion (aquatic)

Response and Reproduction

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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 sexes  sexual reproduction  Males directly transfer sperm to females  Ex. Barnacle stretches out appendage to local females  Mating occurs after female molts

MOVEMENT

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

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/c ommons/6/62/Cicada_molting_animate d-2.gif

Groups of Arthropods

  Classified by number of body segments and mouth parts 3 major groups 1. Crustaceans 2. Spiders and their relatives 3. Insects and their relatives

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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.

Abdomen Cephalothorax Antennae Antennules Mandible

Body Plan of Crustaceans

swimmerets

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Cephalothorax

– Fusion of head with the thorax

Mandible :

– Mouthpart adapted for biting and grinding food

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 glands Spinnerets

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

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Parts

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

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

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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.