Arthropods - General 1409/1409lecnotes/LNExamIV... · 2011-05-25 · most successful animal group...
Transcript of Arthropods - General 1409/1409lecnotes/LNExamIV... · 2011-05-25 · most successful animal group...
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 1
Arthropods - General
1,100,000 known species; at least 2-50 M more species
includes: crabs, crawfish, shrimp, spiders,scorpions, mites, ticks, millipedes, centipedes,insects (dragonflies, butterflies, ants, wasps,beetles, etc)
“jointed legs”
more species in this phylum than in ANY phylum of ANY kingdom of life
includes 2/3rds of all known animals
possibly 50 Million not yet described
one of the most ancient phyla
one of the few that existed before the Cambrian explosion
rich fossil record
many unusual forms now long extinct
very active and energetic animals
very adaptable body plan
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easily modified for a wide variety of lifestyles
more widely distributed over the earth than any otheranimal phylum
live in virtually every habitat on earth
in terms of numbers of individuals:
200 M individual arthropods for everyperson on earth
most <6 mm long
largest: Japanese crab 19’ (5.79 M), 40lbs (18kg)smallest: mite <0.1 mm
tremendous economic importance to humansfoodpollinationdrugs, dyes, silk, honey, waxcrop pestsvectors of disease
were the first animals to move onto land
Silurian 420 MY ago
were the 1st animals to fly
150 MY before flying reptiles, birds, bats
insects 330 MY; Carboniferous
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pterosaurs 170 MY;late Jurassicbirds 150 MY; (coexisted with pterosaurs
for ~90 MY)bats ~40 MY; late Eocene
opened up a whole new set of ecosystems andhabitats
before anything else began to compete for thesame resources
allowed wide and rapid distribution anddissemination across the globe
Body Plan
well developed head (cephalization)
with numerous sense organs
antennae & compound eyes are characteristicsense organs of arthropods
brain (ganglia)
several pairs of feeding appendages
segmented body
allows infinite possibilities for adaptivemodifications
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lots of fusion of segments into a variety of body plans:
cephalothorax & abdomen
head & trunk
head - throax - abdomen
paired jointed appendages
also highly adaptable: walking, swimming,feeding, flying, breathing, reproduction, senses
Body Wall
body is completely covered with hard exoskeleton
also folds into mouth and anus to form lining of foregut and hindgut
cuticle also lines tracheae
excellent for protection
also waterproof good for life on land
main component is chitin (a starch) but much thickerthan the chitin of previous animal phyla
chitin is further hardened with proteins and calciumdeposits
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exoskeleton is secreted by epidermis
often highly colored:camoflagerecognitionwarning
exoskeleton consists of many separate hardened plates
with flexible hinges between
areas where cuticle hasn’t been hardened
muscles are attached to fingerlike inner extensionsof skeleton (=apodemes)
when muscle pulls it moves part
eg. lobster closes claws
the exoskeleton also contains various folds, flaps andspines:
parts modified for feeding
structures for respiration, swimming & mating
some act as sensory organs
with the advantages of this exoskeleton it has one
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major drawback:
animals can’t grow without shedding and regrowing a larger exoskeleton
Molting
problem is solved by molting
a complex process requiring environmental factors and the interaction of various hormones
eg. insects go through a fixed # of molts tilladulthood, then they don’t molt anymore
eg. spiders molt indefinite # of times throughouttheir lives
a. molting is usually initiated by environmentalcues or a buildup of pressure in the body
causes the release of molting hormone (=ecdysone)
b. old cuticle softens and separates from body
c. animal extricates itself from old cuticle
animal is especially vulnerable at this point
eg. soft shell crab
must also shed lining of intestine and tracheaeat same time
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d. animal inflates itself and allows new cuticle to harden
still, the advantages must have greatly outweighed the disadvantages of an exoskeleton
Movement
virtually every form of animal movement is found in arthropods: walking, running, crawling, burrowing, swimming, flying, etc
arthropods have a very complex muscular system
the jointed plates of the body and legs provide attachment point for muscles
similar to muscle bundles that move ourbones
insects have more muscles than most animalsincluding us
eg. humans have ~700 individual muscles; some insectshave 900 or more muscle organs; some caterpillars
have 4,000
Feeding & Digestion
virtually every mode of feeding: carnivores, herbivores, omnivores, parasites
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head appendages modified into a variety ofmouthparts
two main varieties:
chelicerae pinchers or fangs
mandibles jawlike
with numerous accessory feeding appendages
well developed complete digestive tract:
mouth - esophagus - stomach - intestine - anus
with specialized areas for grinding and storing food
accessory glands that secrete enzymes and digestive juices
efficient areas for absorption of nutrients
Respiration
need some kind of respiratory system since waxy cuticle is impermeable to air
arthropods use a variety of respiratory systems
gillsbook gillslungs
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book lungstracheae
Circulation
simple open circulatory system
coelom becomes haemocoel
has beating heart
Nervous System
similar to annelids:
dorsal brain and double nerve cord with pairedganglia in each segment
Excretion
efficient excretory system
prevents excessive water loss on land
Reproduction and Development
mostly dioecious
lots of variation in developmental stages
often quite complex
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eg. larva metamorphosis adult
larvae = caterpillars, grubs, maggots
eg. nymph juvenile adult
eg. some aquatic forms with free swimming larval stage
= nauplius
often with complete change in feeding andlifestyles
eg. aquatic larva vs terrestrial adult
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Classification
Major Subphyla:
1. Trilobites
4,000 species
all extinctmostly marine
2. Myriopods (centipedes & millipedes)
14,000 species
“many feet”centipedes and millipedesmostly terrestrialdistinct head with mandibles & 1 pr antennaemany similar segments
3. Chelicerates (spiders & scorpions)
74,000 species
spiders, crabs, ticks, mites, scorpionsancient groupmostly terrestrialchelicerae and pedipalps for feedingno antennaecephalothorax
4. Crustacea (shrimps and crabs)
67,000 species
shrimp, crab, barnacles, crayfishmostly marinea few freshwater and terrestrial forms
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mandibles, 2 prs antennaemany appendages & many different kinds of appendagescephalothorax
5. Insects
1,100,000 species
most successful animal group87% of all arthropods62% of all animals50% of all life on earth
mostly terrestriala few freshwater, hardly any marinedistinct head with mandibles & 1 pr antennaebody consist of head, thorax and abdomen3 prs of legs, most with 2 prs of wings
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Trilobites
completely extinct group; 4,000 fossil species
earliest arthropod group
appeared before the cambrian explosion
flourished during Cambrian and declined by ordovicianbecame extinct at tend of Permian
lasted 300 MY
marine bottom dwellers (benthos)
some could burrow into the sediment
could roll up like pill bugs for protection
dominated marine benthos for 200 Million years
named for the division of the body into 3 longitudinallobes
most 2-7 cm; largest 70 cm (~2.5’)
distinct head with antennae and compound eyes
heads of many were armed with long sharp spines
not sure of any specialized mouthparts
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thorax of 2-29 segments
segments added as animal grew
each segment had pair of branching appendages
one portion a walking leg
the other probably a gill
base segment of each leg had bristles or teeth
probably used to grind food and move food toward mouth
posterior end of several fused segments
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Myriopods(centipedes & millipedes)
myriopods = many feet
mainly centipedes and millipedes
mostly terrestrial, many freshwater, very few marinespecies
body plan: head & long segmented trunk
1 pair of antennae
mandibles for feeding
appendages on each segment
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Myriopods: eg Centipedes
“100 feet”
3000 species
some tropical species grow to 25 cm (10”) long
usually found in cool, moist habitatsunder longs and rocks
on each of the body segments is one pair ofwalking legs
from 15 to 191 pairs
but none have 50 pairs (its always an odd #)
Feeding and Digestion
most are very active nocturnal predators
mainly use antennae to detect prey;
eyes not well developed
smaller ones eat worms and insects
larger ones, such as Scolopendra of Texas, can eat lizards and small mice
mandibles are primary feeding appendages
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1st pair of trunk appendages is a pair of poison fangs tosubdue prey
apparently not harmful to humans
sting causes slight paindisappears in a few hours
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Myriopods: eg. Millipedes
>10,000 species
“1000 feet”
usually in moist dark places
under logs and stones
can burrow through rotting logs
body usually round in cross section
but locally, flattened millipedes are more common
millipedes are “double footed” 2 prs legs/segment
none have 1000 feet
most have fewer than 50 legs (25 prs)
maximum 752 legs (376 prs)
=Illacme plenipes; endemic to small area in California; thoughtextinct until rediscovered in 2006
some can curl up like pill bugs for defense
Feeding & Digestion
most are scavengers:
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feed mainly on decaying vegetation
a few are herbivores
feed on living plants
much less active than centipedes
eyes not well developed essentially blind
mainly use antennae as primary sense organ
some are able to spray defensive chemicals from“stink” glands along sides of body for protection
eg. toxins, irritants, HCN, prussic acid
eg. a European species secretes a tranquilizer similar toquaaludes
predator (eg spider) eating itbecomes totally relaxed for several days
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Chelicerates(spiders & scorpions)
an ancient group with good fossil record
include horse shoe crabs, sea spiders, scorpions,spiders, ticks, mites, sea scorpions
most are fairly small; some fossil sea scorpions(eurypterids) were 5-6’long; a few up to 9’
most members of the group are terrestrial
1s t group of animals to successfully make transition to land
oldest known fossils of terrestrial animals arechelicerate arthropods from 420 M years ago (Silurian)
Distinctive Characteristics of Chelicerates:
1. named after their main feeding appendage
chelicerae (pincer-like or fang like)used to grab or pierce or tear prey
2. most also have second feeding appendage= pedipalp
3. only arthropod group without antennae
4. most have 4 pairs of walking legs
5. head is fused to thorax = cephalothorax
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Chelicerates: eg Water Scorpions
extinct group
lived from Cambrian to the Permian (especially Silurian & Devonian)
largest of all fossil arthropods
some up to 6’ long
body plan is a blend between horseshoe crabs andscorpions
cephalothorax with simple and compoundeyes, chelicerae & pedipalps
4 pr of walking legs
last pair of appendages paddlelike for swimming
segmented abdomen
spikelike telson
sluggish bottom dwellers
marine, brackish and probably freshwaters
feeding:
probably ate mostly trilobites
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they were the killing machines of the oceans
one paleontologist: “ I’d much rather be in a pool with a6’ shark than a 6’ eurypterid”
Eurypterids may have been the first animals to moveonto land
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Chelicerates: eg. Horseshoe Crabs
also an ancient group; but still survives today
almost unchanged for 300 million years
can grow up to 2 feet in total length and weigh up to10 lbs
Body Form
large cephalothorax, abdomen & telson
cephalothorax with compound and simple eyes
largest chelicerae of the group
pedipalps resemble the 4 pr of walking legs
all but the last pair of walking legs have “pinchers”
the last pair have small paddle-like processes for swimming
Feeding & Digestion
eats clams, snails and sandworms
mouth is in center of legs chews food with bases of legs = gnathobases
have stiff spines
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uses chelicerae to help get and break up food
Respiration
breaths by flat, leaflike book gills on underside ofabdomen
they are also used for swimming
Reproduction & Development
spawn in early summer
arrive by millions on Atlantic beaches
female burrows into sand to lay eggson beach
males deposit sperm on the eggs then femalecovers them with sand
eggs hatch into larvae = trilobite larva
Ecological and Human Impacts
eggs are a valuable food source for migrating shorebirds
overharvesting of horseshoe crabs hascorrelated with a decline in shorebird numbers
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are the most important food source for loggerheadturtles
used by humans as cheap fertilizer for past 100 yrs
pharmaceuticals are also extracted from them
millions are taken to be used as bait
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Chelicerates: eg. Scorpions
~1400 living species
mainly in tropics and subtropics
especially deserts
secretive
active at night = nocturnal
usually stay in underground burrows in day
Texas has 18 species of scorpionsAustin has 2 species
Body Form
cephalothorax short, abdomen much longer
cephalothorax
contains large median eyes
2-5 pairs of smaller lateral eyes
no antennae
small chelicerae and very large pedipalps
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4 pair of walking legs
abdomen
subdivided into a wider part and a thinner tail-like section
at tip of abdomen is stinger
Feeding & Digestion
come out at night to prey on spiders and insects
detect prey by sensing vibrations in sand with hairs onlegs and possibly pectines
large prey are subdued by injecting paralyzing venomfrom stinger at tip of tail
rarely sting humans only if provoked
venom is a neurotoxin that causes paralysis
very painful but rarely fatal
in children the more poisonous species may causeconvulsionsvomitingeven death
a few are deadly to humans
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~25 of the 1500 species (2%)
none in Texas
eg. Centruroides
found in Mexico
kills 100’s – 1000’s/yr in Mexico
effect of poison is very rapidimmediate drowsinessexcessive salivationsluggish tonguesevere contractions of jaw musclesfever to 104 or 105may be hemorrhaging in stomach, lungs and
intestineswaves of convulsionscardiac irregularitiesbreathing difficulties
death usually occurs in <3hrs
if patient lives this long will probablysurvive
Reproduction & Development
scorpions have an elaborate courtship ritual and showparental care like spiders
male and femalehold each other by pinchers (chelae)touch cheliceraeand dance back and forth
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male then stings female to subdue her aggression
does not permanently harm her
male deposits spermatophore on ground(a solid packet of sperm)
male maneuvers female until her genital pore is overthe spermatophore
she flips open lid of spermatophore releasing sperm into her genital opening
in some species male then flees; in others he remains to be cannibalized
provides food to nurture young
development can take up to a year
scorpions bear live young
embryos develop inside mom
development may take several months to a year
absorb nutrients from mom
at birth 1-100 babies are are born
after birth, babies climb onto mom’s back
she carries them around for a week or sobefore they set out on their own
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Chelicerates: eg. Spiders
large group; 40,000 species
Body Form
two part body
cephalothorax and unsegmented abdomen
separated by small pedicel
cephalothorax
simple eyes can detect movement
in some eye may actually form image
some very good vision
eg. jumping spider, Portia, has eyes with spatial acuitybetter than most mammals and birds (better thana cat or pigeon)
most have chelicerae modified into a“switch-blade” like fang
extends and injects venom from poisongland into prey
then retracts like pocket knife
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pedipalps help in manipulating food
also sensory
and to transfer sperm to female
4 pair of walking legs
with sensory setae
tactile; cover legs and detect vibrationsin web and in air
abdomen
with spinnerets for webmaking
Feeding and Digestion
all are predators
fang-like chelicerae inject venom into prey
venom can be:
1. neurotoxin
affects nervous system and musclesto cause paralysis or death
2. digestive enzymes
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digest proteins to kill and liquify prey
after biting prey, spider backs off while toxin kills orparalyzes it
many spiders wrap prey with silk to further immobilize it
after prey has been subdued spider liquifies prey with digestive enzymes
eg. one African spider can liquefy a 2” fish or smallsnake in <3 hrs
spider then uses pharynx and “pumping stomach” tosuck up liquefied prey
spiders have very low metabolism:most can live for long periods without eating
eg. tarantulas several monthseg. Black Widow 200 days
Spider Webs
virtually every aspect of spider biology depends on itsability to produce silk:
used to wrap prey
silk is also used in web as “trip lines”
males produce sperm webs
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females weave coccoons and build nursery webs
juveniles use it to “balloon” to new habitats
spiders have six different kinds of silk glands
each produces a different kind of silk:
sperm webdrag linecoccoonvarious parts of web
silk is made of liquid proteins (keratins) that hardenas it is secreted from glands
silk is extruded from spinnerets
tension of pulling out silk changes its structurefrom a liquid to a solid string
silk is stronger than steel of same diameter
after use it is eaten and amino acids are recycled intonew silk
3 basic types of webs:
1. sheet web
most commonleads to funnel shaped retreat in which spider awaits preyconspicuous on lawns after heavy dew
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2. cobwebs
loosely wovendepend on sticky threads to snare prey
3. orb web
most intricate geometrymost well knowngeneral pattern varies by speciesspider plucks web to determine where prey is
located in web
some other variations of web and silk use:
eg. Bola Spidersproduce single sticky strandthey throw at flying insects (eg moths) to
catch them
eg. many spiders live in webs of other spiderseat host’s prey or host
Reproduction
when ready to reproduce male stops feeding
constructs “sperm web”
deposits drop of semen on it
picks up and stores semen in tip of pedipalp
goes in search of a mate
female is detected by pheromones
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copulation is usually preceded by elaborate courtshiprituals
to ensure the female doesn’t treat suitor asprey
if successful, male inserts pedipalp with sperm intofemale genital opening
after mating male goes out in search of anotherfemale
female remains in web and deposits 100’s or 1000’s ofeggs in egg web
often lots of maternal care
Examples of Spiders
the two most dangerous spiders in US areBlack Widow andBrown Recluse.
both are common in Texas
both have a tendency to live in homes, outhouses and outbuildings
eg. Black Widow
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has been found in all 50 states; common in centralTexas
female is the most venomous
venom is a neurotoxin
venom is 15x’s more toxic than that of aprairie rattlesnake
but so little that only ~1% of bites are fatal
native Americans of California rubbed arrows withmashed spiders for more effective hunting
causes synapses to release Ach causing:muscular spasmsabdominal rigiditycrampssweatingsalivationhigh blood pressuresometimes convulsions
eg. . Brown Recluse
So Central US include Texas
venom contains digestive enzymes
its venom contains enzymes that destroyblood cells
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this induces WBC’s to attack surroundingtissues
creates large crater-like wounds that mayrequire months to heal
its bite can be fatal to children
eg. Phoneurtria sp. (Brazilian wandering spider)
also called banana spiders but NOT the same as the relatively harmless Nephila, also called banana spiders
most dangerous of all spiders
most toxic venom
Costa Rica and throughout South America east of theAndes
large spiders: 10-12 cm (4-5”) leg span
very aggressive
will attack anything (including humans) who appear aggressive
wander the jungle floor at night
in day they hide inside termite mounds, under logs and rocks or in banana plants and bromeliads
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species responsible for most spider bite deaths
in some bites very little venom is released;in others a large amount is injected
bite can cause:
intense pain
sweating
acute allergic reaction
uncomfortable penile enlargement - can lead to impotence(being studied as erectile dysfunction meds)
death (esp in children injected with large dose)
eg. Camel spiders (=wind scorpions)
mideastern species
have reputation as one of the nastiest arachnids but arerelatively harmless
its said they are bigger than a human hand, extremelyaggressive, will climb onto the belly of a camel andeat the camel alive
truth: they are as large as a 5 yr old child’s hand, they can runup to 10 mph (still fastest known nonflying arthropod) and don’t eat camels or people
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Human Impacts of Chelicerates:
most arachnids, though feared, are actually harmlessto humans
1. spiders are directly beneficial as predators each kill 1000’s of insect crop pests
2. large infestations of some mites can damage foodand ornamental plants by sucking their juices
2. Venomous species a few are deadly
eg. black widow
eg. brown recluse
eg. scorpions, esp Centruoides
3. Arachnid Diseases and Parasites: mites & ticks
Future Applications
scientists are experimenting with venom genes touse as biological control against insect pests
venom gene in virus infect & kill insect pest
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Crustaceans(shrimps & crabs)
=shelled creatures; “the insects of the sea”
~67,000 species
eg: lobsters, crayfish, shrimp, crabs, water fleas,copepods, barnacles, pill bugs, etc
crustaceans are mostly aquatic, mostly marine
inhabit most waters of the earth: ocean , arctic , freshwaters, high mountain creeks and lakes thermal springs, brine waters
many are at the base of aquatic food chainspart of zooplankton
only a few are terrestrial; sow bugs, pill bugs
vary in size from microscopic to 12’
largest is giant Japanese crab up to 12’ from end of claws to tail
some quite colorful: blue, red, orange, yellow, mottled
many crustaceans are bioluminescent
most are free living
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some are commensal
eg. sponges, corals, sea anemones
many are parasites
infect almost all classes of animals
some are sessile (=attached)
eg. barnacles
Distinctive Characteristics of Crustacea:
1. body is divided into a cephalothorax, abdomenand tail
2. only arthropods with 2 pairs of antennae
3. use jaw-like mandibles as main feedingstructures; also maxillae and maxillipeds
4. generally have many pairs of appendages modified for a variety of uses
most are branched
lots of variation between groups
Body Form
in most, body is divided into a cephalothorax, abdomen and tail
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often have carapace extending over abdomenand gills
in some groups carapace forms clamshell like valves that encloses body
in some crustaceans the exoskeleton isparticularly thick and reinforced by calciumcarbonate deposits
eg. crab claws
abdomen usually with pairs of jointed appendages onmost segments
generally have many pairs of appendages modifiedfor a variety of uses:
sensoryfeedingdefensewalkingswimmingreproductionrespiration
lots of variation between groups
eg in decapods (crayfish, crabs, lobsters, etc):
1st 2 pair antennae with chemoreceptorsnext 5 pr (3-8) feeding appendages; including
mandible, maxilla and maxillipedsnext 5 (9-13) walking legs including cheliped and
gillsnext 5 (14-18) called swimmerets; used to carry
eggs and as copulatory organ
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last (19) uropod = swim fin
most crustaceans can cast of legs or pinchers andregrow them
Feeding & Digestion
great variation in feeding types:
many are predators
some with appendages that cock and fire to produce pressure waves that stun prey
eg. mantis shrimp
some are suspension feeders
eg. barnacles sit upside down in shell and uselegs to strain water for food
some are scavengers
use jaw-like mandibles as main feedingstructures
well developed digestive system:cardiac stomach with gastric mill for grinding
gastric mill has hardened “teeth”
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pyloric stomach for sorting
digestive gland
Respiration
no special organs in small crustacea
exchange across body surface
in larger crustacea respiration usually by gills
on bases of walking legs
in some sides of carapace form gill chambersthat enclose gills
have an appendage called a “bailer” thatcreates a water current across gills
Sense Organs
sense organs are well developed
most have compound eyes and simple eyes
chemoreceptors (taste) on mouthparts and on the s2pairs of antennae, and on other areas
statocysts for orientation, at base of antennae
saclike; opens to surface by pore
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take in sand grains which trigger hair cells to provide info on orientation
tactile hairs and spines spread over body
Reproduction
most are separate sexed (dioecious)
but barnacles are monoecious
copulation: male delivers sperm packet toreceptacle using swimmeret
some develop large brood sacs for carrying eggs
many marine species have characteristic larval form
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Examples of Crustacea
shrimps, crabs & crayfish
best studied groups
mainly benthic: in and on the sediment
lots of specialized legs
crabs use large claw used to break open shells to feed
fiddler crab uses largest claw for social interactions
only uses small claw for scavenging food from sand
others are filter feeders, herbivores or scavengers
cleaner shrimp remove skin parasites from fish
land crabs burrow above tide line into the water table
can survive days out of water
mantis shrimp is an ambush predator
front end looks like praying mantis
most crab and shrimp carry eggs or brood their young
planktonic crustaceans
small
a large part of the zooplankton in both marine and freshwaters are crustaceans
marine: esp. copepods & krill
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krill can occur in enormous swarms and are a major part of the diet of baleen whales and many fish
freshwaters: esp. water fleas, copepods, seed shrimp
fairy shrimp & brine shrimp
barnacles
often confused with molluscs and originally classified with them
sessile: secrete shell of several calcium plates in which they live
extend feather-like legs to filter feed in the surf
almost all are hermaphrodites yet they cross fertilize with internal fertilization
eggs hatch into motile, nauplius larvae
adults secrete chemicals that attract the larvae to settle near them to facilitate reproduction
preyed on especially by starfish and snails
pill bugs & sow bugs (isopods)
only truly terrestrial crustaceans
have very delicate gill-like respiratory organs that must be kept moist
found in damp places under stones and logs
able to roll up for protection (=rolly pollys)
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young develop in brood pouch
some salt water relatives are found along coasts and live in seaweed, along rocks and algae
some bore into wood causing destruction of pilings and warves
beach fleas(amphipods)
found in both freshwaters and marine habitats
some are almost terrestrial; found crawling around on piers and jettys
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Economic Importance of Crustaceans
many are at the base of aquatic food chainspart of zooplankton
1. as food
eg. crab, lobster, crayfish, shrimp
some crab are harvested by breaking off claws andthrowing rest back
2. many crustaceans are serious pests
a. cause crop destruction
eg. rice crabs in China and India eat rice;burrows may drain rice fields destroying crops
eg. crayfish destroy young cotton plants
b. boring & fouling organisms
borers destroy warves & docks and woodenhulled boats
undermine sea walls and bore into stone
destroy underwater cables
adhere to ships reduce efficiency and increasehull decay
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eg. barnacles
3. some act as intermediate hosts for human parasites
eg. Guinea wormlarva is in copepods; swallowed in contaminated watergrow in lymphatic systemup to 3’ longfemale produces blister like lesions on lower extremeties to
lay eggs in water
eg. fish tapewormlarva in Cyclops and Diaptomuseaten by fishhumans eat uncooked fish
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Insects
1.1 M species; may be as many as 50 M
there are more species of insects than all other animalspecies
entire field of study = Entomology
most successful & widespread group of all animals
adapted to land before most other terrestrial animalsexcept a few Chelicerates
(Devonian 390 MY)
adaptations to land (even deserts):waxy cuticlevarnish layer can close spiraclesextract & retain fluids from food and metabolism
(some don’t need any liquid water at all)diapause & resistant eggs
had 40 MY to evolve and diversify before seriouscompetition for space and resources from other animal phyla
by carboniferous (~300MY ago ) there many differentkinds of insects
still no birds around yet
still not a lot of parasites of insects yet
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eg. roaches were the main insects of the time
eg. some dragonflies had 2’ wingspans
today insects have spread into all major habitats
dominant fauna of all freshwater and soil habitats
some live in deep underground caves
on top of world’s highest mountains
some insects live in unusual habitats:
some flies occur by the millions in brine lakes eg. Great Salt Lake, where hardly any other life forms are able to survive
some insects live in hot springs up to 120º F (49º C)
many species are found inside ice in anarctica
larvae of petroleum flies live in pools of petroleum around oilwells
a few insects have been found breeding in brine vats holdinghuman cadavers at medical schools
the “short-circuit beetle bores into lead cables
butonly a very few are truly marine; Why?
most are <2.5 cm
small size helps them escape enemies
need very little food to sustain themselves
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range from < 1 mm to 25 cm
eg. Atlas moth of India has a wingspan of almost 1 foot
eg. Walkingstick of India is up to 15” long
insects invented agriculture & animal husbandry
many ants and termites cultivate fungi within their burrows
some ants guard aphids that let the ants “milk”them for nectar-like secretion
may have invented slavery
there are ~35 species of “slave making ants” that regularlyraid the nests of other ant species and take young back totheir own colony
there they work as they would in their home colonysearching for food, raising young, etc
always very closely related species
ants will always do the work of whatever colony they are inwhen they emerge as adults
were the first animals to fly
130 MY before pterosaurs
insects: 330 MY(SN04); carboniferousreptiles: 200 MY pterosaurs; late jurassic ,birds: 150 MY; coexisted with pterosaurs for~90MYbats: 54 MY (Eocene)
Distinctive characteristics of Hexapods
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 54
1. body divided into head - thorax - abdomen
2. 1 pair of antennae
3. mandibles for feeding
4. three pairs of walking legs
5. usually 2 pairs of wings
Body Form
body in three parts: head, thorax and abdomen
Head
large compound eyes
several (usually 3) simple eyes (=ocelli)
1 pair of antennae
many kinds of antennae
eg. grasshoppers, crickets and cockroaches have longantennae
eg. butterflies have knob on end
eg. moths antennae are featherlike
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 55
antennae are very complex sense organs in which different segments control different aspects of an insects life:
eg. in ants:one segment detects nest odor and helps prevent
an ant from entering the wrong colony
another segment identifies offspring of a specific queen
another segment detects the ants own feeding trail
another segment helps detect what is needed by the immature ants it is tending
etc
mandibles and other mouthparts for feeding
Thorax
divided into three segments
each thoracic segment bears 1 pair of legs
total 6 legs; thus hexapods
most insects also have 2 pairs of wings on thorax
wings are extensions of cuticle formed byepidermis
Abdomen
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segmented (10-11 segments)
reproductive organs
females have pincher like or syringe likeovipositor to lay eggs
Insect Movement
most kinds of movement are created by muscular system (striated muscles like us)
insects have a more elaborate muscular system thanany other invertebrate group
insects have more muscles than most animalsincluding us
eg. humans have ~700 individual muscles; some insectshave 900 or more muscle organs; some caterpillars
have 4,000
insects are remarkably strong, given their small size
eg. a bee can pick up 50 times its weight equivalent to human carrying 4 tons
eg. beetles are the strongest insects equivalent to us carrying 5 tons
[but their small size relative to weight makes them appear strong if insects were as large as humans they would be little ifany stronger than us]
A. Legs
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great diversity of leg types:
insect legs are adapted for the same kinds ofmovements as vertebrates:
walking, running, jumping, swimming,digging, climbing, grasping
sometimes modified for
jumping (grasshoppers, crickets, fleas)
eg. grasshoppers can j ump 20 times length ofbody
equivalent jump for human would be1/3rd length of football field
eg. fleas are probably the best jumperscan jump 8 “ high and 13 inches in length
equivalent feat in human leap tall bldg in a single bound
storage of pollen (bees)
swimming (diving beetles, many insect larvae)
B. Wings
most insects have two pairs of wings
some use both pairs to fly (eg. butterflies)
some the 1s t pair cover and protect second pair(eg. beetles)
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a few have only 1 pair (flies, mosquitoes)
a few are wingless (lice, fleas)
Insect Flight
insects were the first animals to fly 130 MY before any other animal
the rate of wing beating varies considerably:
fastesteg. midge >1000bpseg. housefly beat ~200bpseg. mosquito ~300bpseg. honey bee ~ 190bps
more typical beat:eg. locust ~20bpseg. dragonfly ~25bps
slowly beating:eg. white butterfly ~12bpseg. swallowtail ~5bps
speed of insect flight varies greatly:
from slowest insect flight speeds:eg. mosquitoes ~2mpheg. houseflies ~5 mpheg. butterflies ~6mpheg. honey bee ~7 mph
to quite fasteg. hawkmoth ~35mpheg. horse fly ~30mpheg. dragonflies 25 mph
flight greatly improved dispersal ability
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 59
some insects are able to migrate 1000’s of miles or fly at high altitudes:
eg. monarch butterfly flies slowly ( 6 mph)but can fly 100’s of miles at a time
eg. painted lady migrates 4000 miles
eg. some butterflies have been seen at 20,000’
some wings are only temporary structures
eg. males and queen ants use wings only for mating flight, then they drop off
Feeding & Nutrition
insects feed upon almost every kind of organic substance
all insects share the same basic mouthparts:mandibles jawshypopharynx tonguelabrum, labium lipsmaxillae
the same basic mouthparts are modified in manyways to facilitate feeding types:
a. most feed on plant juices and tissues
eg many caterpillars feed on specific plants
eg. in butterflies the maxillae form a long coiled food tubefor sucking nectar
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 60
b. many feed on dead or decaying organic matter
eg. beetles and insect larvae are
eg. in houseflies the labium forms a sponge-like feedingstructure
c. some are predaceous
d. some are parasitic
the digestive tract is a tube divided into 3 major regions:
foregut crop, salivary glands, stomachinitial food processing & temporary storage
midgut usually has sac-like gastric caecae enzyme secretion and absorption of nutrients
hindgut intestine and rectumrectum for water and nutrient absorption;
Respiration
an insects blood does not carry much oxygen
oxygen is delivered directly to body cellsthrough system of tubes and passageways
tracheal system with spiracles adaptation to air
many spiracles have valves
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lined with cuticle must be shed
gas movement by diffusion
larger insects use some kind of ventilationeg. pumping movement of abdomen
Sense Organs, communication & behavior
most insect sense organs are microscopic in size andare found on the body wall and variousappendages:
1. Touch
small hairs on body generally respond to touch
most touching involves antennae and mouthparts
these touch receptors can also pick up vibrations inair to respond to wind or gentle breeze
eg. a fly avoids a swat by ‘feeling’ the air being pushed byyour hand as you try to swat it
can also detect temperature, humidity, gravity
touch receptors are used to:
a. recognize nest mates
eg. mole cricket uses antennae to recognize nymphs indark burrow
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eg. social insects can detect unwelcomed visitor totheir nest and attack them
b. social insects often stroke and groom eachother with antennae and mouthparts
c. waggle dance of honeybees involvestouching to communicate location of pollen
2. Vision
two kinds of photoreceptors in insects:ocelli usually 2 or 3 on head
can detect only light vs dark
compound eyes
with many individual lenses = facets
provide a wide field of view andparticularly good at detectingmovement
3. Hearing & Sound
insects have many different kinds of organs forhearing
many insects have hearing organs inside theirlegs that respond to vibrations passingthrough the ground or a plant
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eg. ants come out of nest if you stomp on theground
cicadas and crickets detect sound with anear-like tympanum
sound may be used to attract individuals of thesame species
eg. males and female mosquitoes are attracted to eachother by sound of their buzzing wings
eg. tapping sound of death watch beetles (eat woodon old house -heard by those keeping watch overdead person before burial) used to attract a mate
many insects that can hear have structures formaking various sounds to communicate witheach other or to other species
some rub body parts together to make sounds= stridulation
eg. chirping sound of crickets, katydids, beetlesand ants
some have drum like membrane that canvibrate to make a sound
eg. cicadas are loudest of all insects can be heard half mile away songs differ for each species
hissing cockroach blows air out its spiracles tomake sound
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4. Taste, Smell & Chemical Communication
chemoreceptors are found on all parts of the insects body
on setae, antennae, mouthparts, legs
but are mainly on antennae and feet
wasps and crickets know where to lay eggsbecause they have chemoreceptors on their ovipositors
most insects have the same 4 taste sensations asdo humans: sweet, sour, bitter and salty
organs of smell do not detect as many differentodors as does a human nose
but it is tuned more finely
can detect differences between verysimilar chemicals and in much lesseramounts
eg. male of lesser emperor moth can smell thepheromone of the female up to 6 miles away
some can detect airborne chemicals 5 milesaway
used to find suitable plant for laying eggsflies to find dead animalssome parasitic wasps can track host species
chemical pheromones are used to communicate
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within a species, respectively
eg. sex pheromones attract mates
eg pheromones that cause grouping behavior
eg. ants release alarm pheromones if disturbed orthreatened
eg. ants, caterpillars and other insects produce trailpheromones to map route to food
allomones are chemicals produced by one speciesthat affect another species; defensivechemicals
eg. stink bugs produce defensive allommones to wardoff other species
some of these chemicals can be painful andcause temporary blindness
eg. Bombadier beetle
in addition to external senses insects also have avariety of proprioceptors
can monitor body positions, eg legs and wings,internal pressures
could not walk or fly without this info
Behavior & Communication
insects have keenly developed senses
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 66
can be used for communicationand behavioral responses
insect behavior is mostly instinctive (innate)
eg. caterpillar is programmed to eat a certain plant
but they do have the ability to learn
eg. bee dance
eg. notice landmarks near nest or food
eg. when Colorado potato beetles first attempt to mate,they are not very good at identifying their own species
or even distinguishing head from tail; with repeatedattempts they get better at it
colonial insects (eg. ants, bees) can work muchmore efficiently as a group than any solitary insect
have very structured division of labor
eg. in relative size, ants have one of the largestbrains among insects (equivalent to the processing power of an Apple II computer)
an ants brain contains ~ 250,000 cells a colony of 40,000 has collectively as many cells as a
human brain
Reproduction & Life Cycles
wide range in life spans for adult insects:hours to years
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eg. adult mayflies live for less than a day; do not eat
sole purpose is to reproduce
eg. species with longest lifespan may be a tropical termite whose queen may live for 50 years
most insects also go through several distinctdevelopmental stages as they grow from egg to adult
insects are dioecious
most have internal fertilization
to find mates
most use pheromones
some use light; eg. lightning bugs
others use sound or color
often have courtship rituals
internal fertilization
male inserts sperm into females seminal receptacles
many females mate only once/lifetime and store the sperm
usually lay many eggs
eg. queen honeybee >1 M/lifetime
eg. termites lay 10,000 or more/day
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eg. cockroaches can lay >1 million eggs in a year
but some only 1 egg per mating
some lay eggs on specific plant or animal
many insects “mark” plant with chemical todissuade other females from depositing eggsthere
ID of the chemical they use may beuseful as a natural insect deterrent
some may care for young after hatching
development
insects often have complex development includingmetamorphosis
a. 88% have complete metamorphosis(holometabolous):
egglarvapupa adult
larva usually has chewing mouthparts
pupa is a nonfeeding stage beforemetamorphosis; often in a cocoon
eg. butterflies: larva=caterpillareg. flies: larva=maggoteg. beetles: larva=grub
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 69
once adult emerges it no longer molts
b. most of the rest have incompletemetamorphosis (hemimetabolous):
eggnymph adult
nymph resemble adult without wings
wings develop externally as budlike growths on thorax
grow by successive molts
eg. grasshoppers, cicadas, mayflies,stoneflies, dragonflies
Some insects overwinter as immature stage
don’t complete development until they areliterally frozen in winter months
Defenses
many insects have elaborate mechanisms to avoid predation
camoflage eg. walking stick
mimicry eg. viceroy butterfly
weapons eg. bombardier beetle shoots hot explosive secretions
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 70
toward predator
Diapause
some insects are able to enter a state of dormancy tosurvive adverse conditions; eg temp, humidity
if this dormancy is for an extended period andtriggered by daylength = diapause
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Symbioses
coevolution with plants as pollenators
many ants and termites cultivate fungi within theirburrows
some ants guard aphids that let the ants “milk” themfor nectar-like secretions
eg. termites and protests that digest wood
eg. acacia ants
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Ecological Impacts of Insects
insects are the most important organisms in mostecosystems
1. Important in Recycling of nutrients
eg. 90% of all dead animals (mainly insects) end up as food inant nests
most of the rest of the world is literally helplesswithout them
vertebrates wouldn’t last more than a few months if all insects suddenly disappeared
pollinators for most flowering plants including mostof the world’s crops
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Economic Impacts of Insects
in the US a 2006 study estimates that insects directlyor indirectly contribute more than $57 Billion to oureconomy
1. as nutrition for wildlife insects contribute ~$50Billion/yr to US economy from fishing, hunting, hiking, and enjoying wildlife
2. pest controlinsects often prey on agricultural pests saving upto $4.5 billion/yr in crops and pesticides
3. Pollination services
economic value of insect pollinators worldwide is$217 Billion/yr (08)
in US, excluding honey bees, other insectpollinators contribute ~$3 Billion/yr to agriculture
4. dung beetles burying animal dung help to recyclenutrients, fertilize the soil, and reduce flies and disease carrying insect on grazing land at a value in US of $380 million/yr
5. commercial products
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eg. chitinsecond most abundant organic polymercan be used to coat fruits to slow ripening
eg. beneficial insectsladybugs, etc for natural pest control
6. Venomous Insects
ants, bees, wasps, hornets, blister beetles, etc
some caterpillars have poisonous hairs or spinesthat are attached to poison gland
with any contact spine penetrates skin andinjects poison
eg. asp or pus caterpillar
spines remain poisonous even after they areshed
7. Parasites & Diseases & Vectors
8. Medical applications
maggots used to eat dead tissue from wounds
secrete a fluid containing enzymes that speed healing
will eat and remove ONLY the dead and damaged tissuesand leave the healthy tissues alone
heal some kinds of wounds much more effectively and muchmore quickly than other treatments
Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 75
have produced a prototype gel that healed wounds more quickly
hope to produce wound dressings impregnated with the enzymes
Future Applications
1. blood sucking insect, Dipetalogaster maximus,is used as a high tech syringe
can take up to 4 ml in one meal
donor doesn’t feel a thing
used as a way to get blood samples from wild animals thatare difficult to sample in other ways
eg. can measure stress hormone levels in nesting terns without having to capture them
eg. used to survey rabies infections in batsremoves blood sample using a needle; theyrecover quickly
2. insects as chemical detection devices
insects have extremely sensitive olfactory senses
military and security services need ultra sensitive, flexible and portable odor detectors
sniffer dogscost ~$15,000 each,takes 6 months to trainrequire dedicated handler
“wasp hound” = a portable hand held odor detector
with a team of black wasps as its sensor
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so far the wasps have learned to respond tojust about any odor tried
wasps show coiling behavior when they detectfood molecules
other insects (eg. bees) when they detect foodthey stick out their tongues
they can detect an odor at concentrations of afew ppt
equivalent to finding a grain of saltin a swimming pool
after a couple day stint as sniffers they arereturned to hive and a new batch is trained
can also be used toassure food quality,check for contaminantsmaybe even help diagnose diseases such as
cancer or TB
3. Scientists hope to harness the activities of termitebacteria to break down cellulose to produce ethanol and biofuels