The Arthropods

Chapter 33

General statistics

Most numerous and successful phyla 400,000 known plant species 250,000 known non-arthropod animals Over 1,000,000 species of arthropods.

5 classes of arthropods

General characteristics

Arthropoda: From the Greek word arthron

meaning “joint” and poda meaning “foot”

1) Jointed appendages used for crawling, swimming, flying, etc.

More characteristics

2. Possess an exoskeleton• Made up of protein and chitin• Helps to waterproof and prevent water

loss• Main disadvantage: exoskeleton does not

“grow” with the organism. Must be shed.• molting

3. Segmented body 4. Well developed nervous systems 5. Open circulatory system

Class Crustacea Lobsters, crayfish,

crabs, shrimp. Mostly marine,

some fresh water. All have 2 pairs of

antennae on the head and 2 body regions.

The crayfish

Cephalothorax: fusion of the head and thorax

Antennules: first pair of appendages attached to the head. Shorter of the two pairs of antennae Used for touch, taste, and balance

More appendages

2nd pair : antennae (long) used for touch and tasting

Mandibles (jaws) 1 pair. Used for crushing food

Maxillae: 2 pairs. Used to handle food Maxillipeds: 3 pairs. Touch, taste, handling

of food

Chelipeds

Large first legs where claws are found.

Used for defense and grasping prey.

and more appendages

Walking legs (4 pairs) Swimmerets :

appendages found on the underside of the abdomen.

Used for swimming and carrying eggs and young.

Internal Structure

NUTRITION Food is caught with the chelipeds, crushed

by the mandibles and passed into esophagus.

Food then digested and wastes passed out the anus.

Excretion

Wastes from the blood are removed by the green glands in the head.

Circulation and respiration

Possess a dorsal heart. Open circulatory system (no capillaries nor

veins) Arteries dump blood into open spaces,

sternal sinus collects old blood and channels it to gills to pick up oxygen.

Hemocyanin = copper containing pigment in the blood that aids in transport of oxygen.

Gasses are exchanged at gills:

Nervous system

Well developed sensory organs Compound eyes, many sensory

hairs Statocysts: sacs at the base of the

antennules that aids in balance.

Reproduction

Separate sexes. Can determine sex by looking at first pair of swimmerets.

Male will have enlarged first pair of swimmerets to transfer sperm to seminal receptacle of female during the fall.

Eggs attach to swimmerets and hatch in the spring.

Young stay attached until self sufficient.

Baby crayfish:

Class Chilopoda (centipedes) “centipede” literally means 100 feet Usually 30 to 60 legs, can be as many as

350 legs A distinct 6 segmented head Worm-like body with similar segments.

More centipede facts

All body segments have one pair of legs except the one behind the head and the last two. Fairly fast crawlers

Feed on insects using poison claws. Usually found in dark damp places

Under logs and rocks, in basements

Class diplopoda (millipedes) Literally 1000 legs although no species has

this many legs. World record is 750 legs. Usually anywhere from 100 to 300 legs. Two pairs of legs per body segment except

for the last two segments. Slow moving No poison claws; feed on decaying plant

material.

Class arachnida

Spiders, scorpions, ticks, and mites Mostly free-living. A few parasitic Some are harmful to humans (poisonous

cause disease) Mostly helpful

Get rid of pests like mosquitos

Ticks

Can cause disease ex. Spotted Rocky Mt. Fever Lyme Disease

Lyme Disease

Carried by deer ticks. Caused by a bacterium.

Usually in wooded areas of Mid-Atlantic states and New England.

spiders

2 body segments

1) Cephalothorax (6 pairs of appendages)

2) Adbdomen No antennae or

Chewing jaws

chelicerae

First pair of appendages

Also known as the “fangs” of a spider

Will inject a poison into its prey.

pedipalps

Found between the first pair of legs and the chelicerae.

Used for sensing chemicals and touch

Used to manipulate food.

Abdomen appendages:

4 pairs of walking legs Book lungs = respiratory organs on

underside of abdomen Spinnerets: posterior end of abdomen, used

to make silk for webs and raising and lowering themselves.

Class insecta

Most successful class of arthropods:

30 orders Live in all habitats High reproductive rates (all reproduce

sexually) Small in size Only invertebrates capable of flight

Why is flight such an advantage? Escape form enemies Search for food Allow insects to inhabit environments not

inhabited by other organisms. Less competition for natural resources.

3 body regions:

1. Head (mouthparts, antennae, eyes)

2. Thorax (3 pairs of legs, wings)3. Abdomen (respiratory

structures)

Specialized structures:

Mouthparts

2 main types:

legs

Used for swimming, collecting pollen. Defense, grasping prey, jumping

Incomplete metamorphosis

Series of changes where an insect grows from eggs to a nymph to an adult

Nymph = immature form that closely resembles the adult form except for certain features.

Examples: grasshoppers, crickets

Complete metamorphosis

4 stages: Eggs, larva, pupa, adult Larval stage examples: caterpillars,

maggots Pupa: cocoon Changes are controlled by hormones. ex.

Grasshopper (order Orthroptera)

Head 2 large compound eyes 3 simple eyes 1 pair of antennae Mouthparts located outside the

mouth(mandible, maxilla, special tongue-like organ)

Thorax

3 separate segments to the thorax with each possessing a pair of legs

Each leg has five segments ending in a clawed tarsus or foot

1st and 2nd pairs of legs are for crawling. Last pair used for jumping 2 pairs of wings

Abdomen

Made up of 10 segments Each segment has one pair of spiracles

(openings into air tubes) 1 pair of tympanum (hearing organs) reproductive organs

Female abdomen

Ovipositor = hard four pointed organ at the base of the abdomen used to dig holes for burying eggs.

Harmful effects of insects:

Cause millions of dollars in crop damage.

examples: Corn smut, rootworm, locusts, tent

caterpillars

Images:

Transmit diseases

Malaria = transmitted by mosquitoes West Nile virus = also mosquitoes West Nile link

Destroy property

Cockroachestermites moths

Economic value of insects:

Help pollinate fruit trees Produce honey Kill other harmful insects Eat dead plant and animal material

Ways to kill insects:

Most common: insecticides Trap and sterilize males Genetic engineering

Bt corn

Phylum Echinodermata

Literally means “spiny-skinned” All marine Examples:

characteristics

Well developed coelom Endoskeleton Simplest organism showing

embryological formation of the anus before formation of the mouth.

Radial symmetry

starfish

Usually five arms but can possess up to 20 arms

Extensive water-vascular system Water will enter through the sieve plate and

pass through a series of canals into each arm.

Tube feet

Small water filled tubes or projections on the ventral surface used for locomotion, respiration, grabbing prey, and digestion.

More starfish facts

Feed on clams and oysters Skin gills = small finger-like appendages on

the surface of starfish that is a site for respiration

Separate sexes Can regenerate lost arms. An entire new

starfish can grow as long as part of the central disk is present.

Assignment:

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