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Introduction to Arthropods

• Most numerous and diverse phylum of animals

• 75% of all animal species

• 1 million known species

• Found in every habitat on earth

• Segmented

• Invertebrates

• Have jointed appendages

• Exoskeleton

General Characteristics• Segments are fused into larger regions

• Each segment has a pair of jointed

appendages (ie. extensions of the

body)

• eg. Antennae, legs

• Functions of appendages:

• Movement

• Reproduction

• Sensory

• Defense

• Gathering food

Exoskeleton• Composed of chitin

• Helps prevent desiccation(drying out)

• Sometimes have a waxy layer

• Makes them waterproof

• Provides support and protection

• Attachment for muscles

• Limits growth

• To grow, they must shed their exoskeleton &

grow a new one (ie. molting)

• Vulnerable when molting

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3 Subphyla of Arthropods

• Kingdom

• Phylum

• Subphylum

• Class

• Order

• Two pairs of antennae

• Chewing mouthparts

• Legs with claws

• Examples include:

• Lobster

• Crayfish

• Crab

• Barnacles

• Shrimp

1. Subphylum Crustacea

• One pair of antennae

• Chewing mouthparts

• No claws on their legs

• Examples include:

• Insects

• Centipedes

• Millipedes

2. Subphylum Uniramia

• No antennae

• Pincer-like mouthparts

• No claws on their legs

• Examples include:

• Spiders

• Scorpions

• Mites

3. Subphylum Chelicerata

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� Cephalothorax

� Fused head & chest region to which legs and other

appendages are attached.

� Hard shell (ie. carapace) covers this

� Abdomen

� Long, narrow tail region - divided into seven segments

Crustacean Body Structure Crustacean Systems

A. Respiratory

B. Digestive

C. Circulatory

D. Excretory

E. Reproductive

F. Nervous

A. Respiratory System

• Gills are attached to the walking legs

• Water is pulled up under the carapace during locomotion

• Current of water is sent forward over the gills

• Gills absorb O2 from water and release CO2

• Water exits to the anterior via the second maxillae

• When stationary the gill bailersmove water across the gills so respiration can occur

B. Digestive System• Mandibles crush the food and pass

it on to the stomach

• Stomach pulverizes, strains & sorts food

• Stomach wall has chitinous teeth to grind food

• Smallest particles are sent to the digestive gland for nutrient absorption

• Larger particles are sent to the intestine

• Coarsest particles stay in the stomach to be ground further

• Undigested materials pass through the intestine and out the anus

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• Open circulatory system

• Heart lies dorsally in a sinus of blood

• Heart has three pairs of openings through which O2

rich blood from the sinus enters the relaxed heart

• Valves close preventing blood from exiting the

openings

• Blood is driven into arteries that go to the tissues of

the body

• O2 deficient blood collects in a large sinus

• It enters the gills to absorb O2 and release CO2

C. Circulatory System

• Solid feces are excreted through the anus

• At the base of the antennae is the green

gland (ie. bladder)

• Regulates the amount of salt and H2O in the

blood

D. Excretory System

• Separate sexes

• Male deposits sperm into a special receptacle near the female pores (ie. where eggs exit)

• Fertilized eggs stick to the abdomen for the months that she carries them

• Crustacean hatches from the eggs as a free-swimming larva

E. Reproductive System

• Similar to annelids

• Brain

• Nerve cord

• Compound eyes

• Composed of hundreds or thousands of closely packed lenses

• Well suited for detecting motion

• Important for hunting

• At Night

• Deep water with very little light

F. Nervous System