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Arthropods
“Yet these you may eat of every flying insect that creeps on all fours; those which have
joined legs above their feet with which to leap on the earth.” Leviticus 11:21
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invertebrates: animals without backbones
97% of all species is an invertebrate
Arthropods
• jointed appendages; found in all climates and environments
• phylum: arthropoda (Gr. jointed + feet)
• exoskeleton: composed of chitin; provides protection, strength, support, lightness,
locomotion
• segmented body; dorsal heart; ventral nervous system
• classes [Table 20.1 p. 422]
insects - 70% species
arachnids - spiders, scorpions
centipedes / millipedes- numerous body segments and legs
crustaceans - crayfish, lobsters, crab, shrimp
Insects
• Class: insecta
• entomologist: scientists who study insects
• exoskeleton divided into head, thorax, abdomen
single pair of feelers/antennae
compound eyes
breathe through tracheae
three pairs jointed legs
one or two pairs of wings
• incomplete metamorphosis: [Fig 20.1 p.423]
egg --> nymph molts its outgrown skeleton several times and secretes a new one
• complete metamorphosis: [Fig. 20.2 p. 423]
egg --> larva (worm-like eating and growing stage) --> forms cocoon or chrysalis at full
larva development --> pupa (resting stage) --> adult
Grasshopper
• [Fig. 20.3 p. 424]
• head: front segment
• antennae give grasshopper excellent sense of smell, touch, taste
• simple eyes - three by antennae and between; detect only light and shadow
• compound eye - located on either side of head; composed of many independent
lenses and retinas; sensitive to shape, color, movement; wide angle of vision
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mouth: [Fig. 20.4 p. 425]
diet of plants
labrum/labium - flattened “lips” that guide food into jaws and hold it
mandibles - main serrated jaws move side to side to cut and grind food
maxillae - secondary jaws hold and help chew food
palpus - fingerlike organ that may also taste
thorax: middle section of body
prothorax - attaches to front pair of legs
mesothorax - middle pair of legs, front pair of wings
metathorax - rear legs and rear wings
forewings provide control, hind wings lift and propel
each of legs has five jointed sections:
coxa - attaches to body
trochanter - second segment; +coxa like ball and joint
femur
tibia
tarsus
first two legs for crawling and clinging, rear legs for jumping
abdomen: contains many of insect's vital organs; divided into 11 segments
spiracles: opening for air, allowing access to tracheae
tympanum: single eardrum located on each side of first abdominal segment
[Fig. 20.6 p. 426]
chewed food --> esophagus --> crop (temp storage) --> gizzard (further grinding) -->
stomach (via gastric ceca) --> colon --> rectum --> anus
tubelike heart located in upper abdomen, just under exoskeleton
open system - blood exits aorta at head and flows rearward through open body cavity
around vital organs; reenters heart through ostia, along its sides
Malphigian tubes filter and keep waste and empty into colon
oviduct opens near tip of female abdomen; female stores male sperm in seminal
receptacle until she lays her eggs from ovipositor, then also deposits sperm
Insect orders
• [Table 20.2 p. 430]
Order
Characteristic
Examples
Orthoptera
straight-winged
grasshopper, cricket, roach
Odonata
toothed
dragonfly
Hemiptera
half-winged (“bug”)
bedbug
Homoptera
same-winged
cicada
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Lepidoptera
scale-winged
butterfly, moth (know
differences)
Diptera
two-winged
housefly, mosquito
Coleoptera
sheath-winged
beetle, ladybug
Hymenoptera
membrane-winged
ants, bees, wasps
colonies: hymenopterans with wings
queen bee - egg-laying female; worker larva fed royal jelly produced by workers;
responsible for reproduction of colony; mates several times over few days and collects
sperm to supply for lifetime (1.5-2 yrs); puts each egg in separate cell constructed by
worker bees; unfertilized eggs --> drones, fertilized eggs --> queens or workers
drones - males; larger than worker bees; only function to mate with queen; allowed to
die in fall so new drones develop from eggs laid the following spring
workers - non egg-laying females; feed and care for larvae, clean cells; after few
weeks, can become field bees in search of nectar/pollen or guards; live for weeks
(working season) or several months (fall)
stingers - on queen bees and workers; when used by worker, stinger is ripped from
worker's body along with certain internal organs so bee dies
insects needed for pollination; some harmful by injuring plants or endangering health
of man; types of control: quarantine, agricultural, biological, chemical (pesticides,
insecticides)
Arachnids
• Class: Arachnida (spiders, ticks, scorpions)
• found almost everywhere on earth; true spiders or mygalomorphs (tarantulas)
• body - cephalothorax (fused head and thorax), abdomen
• no antennae; four pairs of legs; simple eyes
• all carnivorous, most venomous
• chelicerae - pair of short appendages below eyes; fangs at end of chelicerae inject
poison
• sprays/injects victim with enzyme-containing digestive juices which predigest solids so
spider can suck up dissolved tissues and body fluid
• four pairs of legs attached to cephalothorax; last leg segment surrounded by pad of
hairs (scopula) that helps to cling to walls and ceilings; spider walks by moving 1st/3rd
leg on one side of body with 2nd/4th leg on other side of body; no muscles to extend
legs --> blood pressure keeps legs extended so drop in blood pressure results in
inability to walk
• (read rest of internal structure, reproduction p. 434-436)
• daddy longlegs - no waist, one pair of simple eyes
• scorpions - stinging arachnids; abdomen tipped with venomous stinger
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mites/ticks - parasitic to man and animals
Centipedes/Millipedes
• centipedes (class Chilopoda): flattened body; single pair of legs attached to each
segment; 30-354 legs (rare to have >50)
• millipedes (class Diplopoda): rounded body; two pairs of legs per segment
Crustaceans
• two pairs of antennae on front of body; cephalothorax + abdomen; two+ pairs of
appendages; exoskeleton; gills
• [Fig. 20.26 p. 438] crayfish (class Malacostraca)
• cephalothorax contains head and thorax
• carapace outer shell, rostrum (forward extension of carapace) protects head
• head: compound eyes, two sets of feelers
antennules - shorter pair; at base are sacs that contain sense organs of hearing and
balance (statocysts)
antennae - large; communicate touch, taste, smell
mandibles and maxillae - chewing appendages
• thorax: maxillipeds - first three sets help keep grip on food
chelipeds - pincers for self-defense
walking legs - locomotion
gills below carapace
• abdomen: segmented; swimmerets - first five pairs, eggs attach during reproduction
uropod - swimmerets on sixth segment; telson extends
[Fig. 20.27 p. 439]
• food through mouth --> short esophagus --> gastric mill (grinds food) --> stomach -->
digestive gland --> intestine --> anus
• gills attached to bases of legs of thorax; gills waved through water every time crayfish
moves
• open circulatory system; colorless blood pumped to ends of body through seven
arteries then returns to heart by flowing through body cavity and collected in
pericardial sinus
• green glands: excretory organs lie in front of stomach and open to outside near base
of antennae; function like kidneys to remove waste and store minerals
• crayfish mate in fall; male deposits sperm in female seminal receptacles where stored
until spring when female lays eggs; attaches fertilized eggs to swimmerets; young
hatch after 6-8wks
• crayfish continue to molt throughout lives; green glands absorb CaCO₃ (calcium
carbonate) from old exoskeleton to reuse
Homework
Section 20.1 #1-7
Section 20.2 #1-7
Section 20.3 #1-6
Section 20.4 #1-6
Finish grasshopper and crayfish labs