The Arthropods Chapter 33
Dec 28, 2015
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:
Page 730 1-17,20,21,22,25,26,27,30,32