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I. Section 31.1 Features of Arthropods
A. Divided into three subphyla; Uniramia (have jaws), Chelicerata or
Crustacea (have fangs or pincers)
B. Arthropods include Arachnids (spiders, scorpions, ticks, and mites),
Insects, and Crustaceans
C. Body Plan
1. jointed appendages - structures that are extended from the body wall
that have joints so that they can bend
2. segmented – individual segments exist only during larvae stage; in
adulthood three regions exist, head, thorax (mid-body), and abdomen.
Some have a cephalothorax (head and thorax are fused together).
3. distinct head, often with compound eyes (eyes made of thousands of
individual visual units, see movement more quickly but not as clearly as
humans)
4. exoskeleton – made of chitin (tough but brittle substance), thinner and
more flexible near joints, muscles pull against exoskeleton for movement,
restricts size of organisms, vary in thickness depending on species
5. respiratory systems consists of tracheae (network of fine tubes) and
spiracles (pores in the body of an arthropod through which air enters)
6. open circulatory system – tissues a bathed directly by the blood
7. malpighian tubules – slender finger –like extensions from the gut that
are bathed in the blood from the circulatory system, allows for exchange of
gasses and nutrients
8. wings – found in many (but not all) arthropods
D. Molting – (also called ecdysis) triggered by the release of hormones,
sheds exoskeleton to allow for growth of organism
II.
Section 31.2
Spiders and Other Arachnids
A. Members of Sub-phyla Chelicerata – arachnids have fangs or pincers in
their mouth called chelicerae
B. Arachnids include spiders, scorpions, ticks, mites, daddy long legs,
marine horseshoe crabs, and sea spiders
C. Body plan
1. have a cephalothorax (head and thorax are fused)
2. first pair of appendages are chelicerae (fangs or pincers)
3. second pair of appendages are pedipalps (used for catching and
handling prey, and sometimes for sensation or reproduction)
4. third through sixth pairs of appendages are walking legs
5. all except mites are carnivores
6. do not have jaws so must consume liquid food (they inject a powerful
enzyme into prey which liquefies the tissues so they can be sucked into the
arachnid stomach)
III. Spiders
A. Chelicerae are modified fangs with poison glands containing toxins to
kill or paralyze their prey, fangs are also used to inject enzymes to liquefy
their food for consumption
B. The Black Widow and Brown Recluse (both common in Mississippi) are
the only two spiders in the US that are dangerous to humans
C. Important predators of insects in all ecosystems
D. All spiders have spinnerets (modified appendages located in the
abdomen used to secrete a sticky silk)
E. “Orb-builders” make beautiful webs to trap food, others use silk for egg
sacs or trapping prey.
IV.
Scorpions
A. Have long slender segmented abdomens ending in a venomous stinger
used to stun prey
B. Abdomen is usually folded over the body making scorpions easy to
recognize
C. Pedipalps are large grasping pincers used for defense, seizing food, and
reproduction
V. Mites
A. Largest group of arachnids, includes chiggers and ticks
B. Head, thorax and abdomen are fused into one part
C. Usually very small
D. Aquatic mites are herbivores, terrestrial mites are predators
E. Most are not harmful but some are very problematic to plants and
animals by passing viral or fungal infections on to their hosts
F. Because they transmit diseases ticks can be very harmful to humans
VI.
Section 31.3 Insects and Their Relatives
A. Most numerous of all animals, over 700,000 names species
B. Belong to the sub-phylum Uniramia (arthropods with jaws)
C. Most belong to one of four orders
1.
2.
3.
4.
Coleoptera - “shield winged”, include beetles and weevils
Diptera - “two winged”, include flies and mosquitoes
Lepidoptera - “scale winged” include butterflies and moths
Hymenoptera - “membrane winged” include ants and bees
D. Primarily terrestrial (land dwelling), usually small but some can grow to
4 feet in length
E. Body Plan
1. The Head contains mandibles (jaws used for chewing), mouthparts
specialized to the eating habits of the species, one pair of antennae, and a
pair of compound eyes
2. The Thorax is made of three fused segments and has three pairs of
jointed walking legs, and most have one pair of wings
3. The Abdomen is made of 9-12 segments
F. Life Cycles
1. Complete Metamorphoses (ex. butterfly and ladybug)
a) Egg
b) Larvae (wingless and worm-like)
c) Pupa (stage occurs within a chrysalis which is a protective capsule)
d) Adult
2. Incomplete Metamorphoses (ex. grasshopper)
a) Egg
b) Nymph (looks like small wingless adult, will molt several times
before adulthood)
c) Adult
G. Flight
1. Insects were the first animals to evolve wings, allowed them to reach
more food sources and escape predators
2. Wings
a) develop from saclike growths on the thorax,
b) made of chitin and a network of air filled veins,
c) most insects have 2 pairs (flies have only 1, fleas and lice none)
d) only one pair of wings is used for flight the other may be modified for
protection or stability
H. Some insects are social - they live and work in communities
1. Hymenoptera (ants, bees, and wasps)
2. Isoptera (termites)
3. Division of labor - different kinds of individuals have specific tasks
4. The roll played by and individual is its “caste” and is determined by
heredity, diet, hormones, and pheromones (chemicals produced by the
insect that are used for communication)
I. Insect relatives
1. Centipedes - segmented with one pair of legs on each, can have up to
173 segments, carnivores
2. Millipedes - segmented with two pairs of legs on each, have from 11 to
100 or more segments, herbivores
VII. Section 31.4 Crustaceans
A. Members of the sub-phylum Crustacea
B. Primarily marine but occasionally found in fresh water and on land
C. Includes crabs, lobsters, crayfish, barnacles, and water fleas
D. Have a larval stage called a nauplius, which will molt several times
before adulthood, has three pairs of branched appendages
E. Terrestrial crustaceans
1. Include pill bugs and sow bugs
2. Live in leafy ground litter
F. Decapods
1. Include shrimp, lobster, crayfish
2. Have 5 pair of legs
3. Anterior legs may be modified into large pincers called chelipeds
4. Appendages attached to the abdomen called swimmeretes may be used
for swimming or reproduction
5. Flattened appendages at the posterior called uropods act like paddles
as they forcefully contract the abdomen to propel themselves through the
water
G. Sessile Crustaceans
1. Include barnacles
2. Have free swimming larval form then attach as adults