Download Arthropods - Killeen Independent School District

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Versatile exoskeleton
Segmentation and appendages for more
efficient locomotion
Air piped directly to cells
Highly developed sensory organs
Complex behavior patterns
Reduced competition through
metamorphosis
 Highly
protective, yet highly mobile
 Exoskeleton: several layers of cuticle


covering secreted by underlying epidermis
Procuticle




Inner, thicker cuticle
Composed of chitin bound with protein
 Tough, resistant, nitrogenous polysaccharide that is
insoluble in water, alkalies, and weak acids
 Crustaceans procuticle impregnated with calcium salts
(<flexibility, >hardness)
Divided into two parts:
 Exocuticle (secreted before a molt)
 Endocuticle (secreted after molting)
Epicuticle


Thin
Composed of protein and lipids
 Ecdysis
(molting)
 Each
segment has a pair of jointed
appendages

can be modified:

Segments and appendages can be specialized for
adaptive functions
 Limb
segments- hollow levers moved by
striated muscles (good for rapid actions)
 Jointed
hairs

appendages- equipped with sensory
Modified for sensory functions, food handling,
and swift/efficient walking or swimming
 Land


arthropods
Highly efficient tracheal system of air tubes
Tubes deliver oxygen directly to tissues and cells
for high metabolic rate
 Aquatic

arthropods
Breath mainly from some form of gill
 Arthropods
are very alert to environmental
stimuli
 Compound (mosaic) eyes
 Other senses of:





Touch (what organ system?)
Smell (what organ system?)
Hearing (what organ system?)
Balance (what organ system?)
Chemical reception (what organ system?)
 Innate


behavior
Unlearned behavior controls much of what
arthropods do
Learned behavior




Habituation (ignore repeated harmless stimuli)
Imprinting (colony scents)
Classical conditioning (food scents)
Waggle dance (bees)
 Larval
forms

Quite different from adults = less competition
within species

Larval forms adapted for fulfilling a different
niche than adults


Different foods
Different habitats
 Subphylum
Trilobita
 Subphylum Chelicerata
 Subphylum Crustacea
 Subphylum Myriapoda
 Subphylum Hexapoda
 Extinct
for over 200 million
years
 Abundant during the Cambrian &
Ordovican periods
 Named for tri-lobed shape of
body caused by a pair of
longitudinal grooves
 Bottom dwellers, probably
scavengers
 Could roll up like rollie-pollies
 Horseshoe
crabs, spiders, ticks, mites, scorpions,
sea spiders, etc
 Characterized by:


Two tagmata
Six pairs of appendages






Pair of chelicerae
Pair of pedipalps
Four pairs of walking legs (exception: horseshoe crabs)
No mandibles
No antennae
Most suck liquid food from their prey

Subclass Xiphosurida
 Class
Pycnogonida
 Class Arachnida




Order Araneae
Order Scorpionida
Order Opiliones
Oder Acari
 Dates

from Cambrian period
Practically unchanged back to
Triassic Period
 Lives
in shallow water along
North American Atlantic coast
 Swims (awkwardly) with
abdominal plates; walks with
walking legs
 Feed at night – worms & small
mollusks
 Physical




Carapace: Unsegmented,
horseshoe-shaped, and hard
dorsal shield
Broad abdomen
Telson: long spine-like tailpiece
Book gills: flat leaf-like gills


Features:
Exposed on some abdominal
appendages
One pair chelicerae and 5 pairs
of walking legs
 Physical


4 pairs of thin, walking legs
Pair of ovigers (ovigerous legs)




Features:
Males carry egg masses on these legs
Reduced abdomen
Elongated cephalothorax
Large suctorial proboscis: suck juices from
hydroids and soft-bodied animals
 Ocean-dwellers
 Few
mm in length
 uber
diverse: > 50,000 species described
 Includes: spiders, scorpions,
pesudoscorpions, whip scorpions, ticks,
mites, harvestmen (daddy longlegs), etc…
 Arachnid tagmata: cephalothorax & abdomen
 >35,000
species worldwide
 Predacious



Feed mainly on insects
Chase prey, ambush prey, or trap them in silk net
Feeding:



Chelicerae function as fangs with ducts from venom glands
Digestive enzymes liquefy tissue so broth can be sucked up
Some have teeth at base of chelicerae to crush or chew in
addition to use of enzymes
 Physical

Features
Tagmata joined by pedicel

Narrow, waist-like structure connecting cephalothorax &
abdomen
2 or 3 spinnerets contain hundreds of microscopic
tubules connect to abdominal silk glands
 Silk thread created when liquid protein secretions
hardens on contact with air
 Fun facts:

silk threads stronger than steel threads of same
diameter
 2nd in torsional strength (fused quartz fiber is 1st)
 Threads will stretch 1/5 of their length before breaking


webs used for:

Trap insects, line nests, form sperm webs or egg sacs,
build draglines, make bride lines, warning threads,
molting threads, attachment discs, nursery webs, or to
securely wrap prey
Orb
Webs
Orb
Webs
Drag
Lines
Egg
Cases
 Most
spiders are harmless to humans
 Australia has some of the deadliest spiders (they
have some of the deadliest
organisms actually)

Atrax robustis
 South

America has a few dangerous spiders too
Phoneutria fera
 In

the U.S.
Black widows




Latrodectus mactans
Venom is neurotoxic (acts on the nervous
system)
Shiny black, red hourglass on ventral side of
abdomen
Brown recluse



Loxosceles reclusa
Venom is hemolytic
(destroys tissues and skin
surrounding bite)
Brown, violin-shaped
dorsal stripe on
cephalothorax

Book lungs or
tracheae (or both)

Book lungs- many
parallel air pockets
extending into a
blood-filled chamber


Air enters chamber by a
slit in body wall
Tracheae- system of
air tubes that carry air
directly to tissues
from opening called
spiracles

Malpighian tubules



K, other solutes & wastes secrete into
tubules
Tubules drain urine-like fluid into
intestines
Rectal gland reabsorb K & H20



Wastes like uric acid
Nearly dry mixture of urine & feces left
Great adaptation (especially for arid
conditions)- conserve fluids
 Coxal

glands
Modified nephridia open @ base (coxa) of
first & third walking legs
8





simple eyes
Lens, optic rods, retina
Perception of moving objects
May form images for hunting/jumping spiders
Generally poor vision
Sensory setae

Hair-like structures that sense surroundings


i.e. air currents, changing tensions in the spider’s web
Web vibrations allow spider to sense size/activity
of its prey, mate, or predator
Courtship rituals before mating
 Indirect mating

Male deposits sperm on a web he has spun prior to
mating
 Sperm package picked up/stored in cavities of
pedipalps
 Pedipalps = second pair of appendages that males use
to transfer sperm into a female’s genital opening

Females can store sperm packets in seminal
receptacle until eggs are ready (weeks or
months)
 Females lay fertilized eggs in silken cocoon



Carries around or attaches to web or plant
Cocoon may contain hundreds of eggs

Eggs hatch and young remain in egg sac for a few
weeks feeding and growing for several molts
 Range:
tropical, subtropical, some temperate
zones
 Secretive: hiding in burrows or under objects by
day; feeding @ night
 Predacious: insects & spiders
 Reproduction


Bear live young
Mother carries on her back until after their first molt
 Venom
can be fatal in a few species from Africa,
Mexico, Arizona, New Mexico, Australia, etc…


Androctonus
Centruroides
 Physical



Claw-like pedipalps
Jaw-like chelicerae
Short cephalothorax



features
1 – 6 pairs of eyes
appendages
segmented abdomen


Preabdomen- broad
Postabdomen- tail-like; ends in a stinging apparatus
that injects venom
 Physical



Broad joining of abdomen with cephalothorax
without pedicel
Presence of external segmentation of abdomen
4 pairs of long, spindly legs


Features
Legs can regenerate
Ends of chelicerae are pincer-like
 Scavenger
feeders
 Fun Fact: NOT the
most poisonous spider.
They do not even have
venom glands!
 Habitat:
fresh/saltwater,
vegetation, ground, parasitic on
vertebrates/invertebrates
 >25,000

Many of which are
important to humans
 Physical


species
Features
Fused cephalothorax & abdomen
(no external tagmatization)
Capitulum- little anterior
projections carrying mouthparts
 Many


Dermatophoides farinae live in
house dust and cause allergies &
dermatoses
Aquatic species (mostly fresh, some
marine)



free living
Long, hair-like setae on legs for swimming
Larvae may be parasitic on aquatic inverts
Spider mites (Family Tetranychidae)

Agricultural pests on fruit trees, cotton,
clover, etc…
 Genus


Larvae are called chiggers or redbugs
Feed on dermal tissues of terrestrial vertebrates



Process:
Cause irritating dermatitis
Some species transmit Asiatic scrub typhus
 Genus

Trombicula
Demodex
Hair-follicle mites
 Genus

Ixodes
Lyme’s Disease
 Feeding


Pierce skin; suck
blood until
distended; drop off;
digest meal
Molts; feeds again
 Disease

vectors
Carry protozoans,
rickettsial, viral,
bacterial, and
fungal organisms
 Genus
Dermacentor
Rocky Mountain
spotted fever
 tularemia

 Boophilus
annulatus
(cattle tick)

Texas cattle fever
(red-water fever)
Lobsters, crayfishes, shrimp, crabs,
water fleas, copepods, and barnacles
 >67,000
species
 Primarily
 Free
aquatic (mainly marine), few terrestrial
living; can be sessile, commensal, parasitic
 Important
to aquatic ecosystems and economy
2
pairs of antennae
 Mandible and two pairs of maxillae
 Typically pair o’ biramous appendages on each
segment (except first antennae)
 Gills (no malpighian tubules)
 16-20 segments (> 60 segments)
 Major tagmata: head, thorax, abdomen

Varying degrees of fusion
 Carapace-
dorsal cuticle of head covers/fuses
with some/all thoracic & abdominal segments;
clamshell-like vales that cover most/all body;
covers entire cephalothorax not abdomen
 Foliaceous


Flat & leaf-like
maxillae
 Biramous


2 branches
Swimmerets, maxillipeds,
uropods, antennae
 Uniramous


1 branch
Walking legs
 Swimmerets-
abdominal appendages, biramous
 Endopod- inner branch of swimmerets
 Exopod- outer branch of swimmerets
 Protopod- basal segments, endo/exopods attached
to
 Maxillipeds- 1st 3 pairs of thoracic appendages
 Chelipeds- 1st pair of walking legs enlarged with
chela
 Gonopods-
1st pair of abdominal swimmerets
used for copulation for males, nursery for
eggs/young for females
 Uropods-
last pair of appendages;
paddles for backward movement
 Telson-
uropods & telson protect
young/eggs
 Epidermis-endocuticle-exocuticle-epicuticle
 Exoskeleton
must be molted during maturation
and growth
 Molting occurs in steps
1.
2.
3.
4.
Old procuticle separates from epidermis, which
secretes a new epicuticle
As a new exocuticle is secreted, mottling fluid
dissolves old endocuticle, and solution products
are reabsorbed
@ ecdysis, the old epicuticle and exocuticle are
discarded
In postecdysis, new cuticle is stretched and
unfolded and endocuticle is secreted
 Chromatophores


Pigments in specialized branched cells
Change color by:


Concentrating pigment granules in
center of cells, which causes lightening
Dispersing pigment throughout each cell,
which causes darkening
 Neurosecretory


Neurosecretory cells in eyestalk control pigment
behavior
Hormones control:


Pigment in eyes for light & dark adaptation
Control rate and amplitude of heartbeat
 Androgenic

hormones
glands
Secretions stimulate expression of male sexual
characteristics
 Controls
molting
 Molt-inhibiting hormone


created by neurosecretory cells in the X-organ of
the eyestalk
released through sinus glands in the eyestalk
 Level
of hormone decreased
 Molting hormone


produced by Y-organs near mandible
Initiates premolt
 Mandibles/maxillae
involved in ingestion
 Maxillipeds hold/crushes food
 Suspension feeders


Plankton, detritus, bacteria
Use legs to create water currents that sweep food
particles through fringe of setae
 Scavengers

Larvae, worms, crustaceans, snails, fishes
 Predatory


Lygiosquilla- a walking leg has specialized digit that can
be drawn into a groove and released to pierce passing
prey
Alpheus- enlarged chela that forms bubble that
implodes to stun prey (like cocking a gun)
 Crayfish

2-part stomach


Gastric mill in 1st stomach
 Food shredded by mandibles ground by 3 calcareous
teeth into fine particles that will pass to 2nd stomach
Particles pass into intestines for chemical
digestion
 Some
small crustaceans breath through body
surface
 Gills



Vary in shape: tree-like, leaf-like, filamentous
Associated blood vessels or sinuses
Attached to appendages usually


Movement through H2O keeps
gills ventilated
Branchial chambers

Protected by overlapping carapace
 Open



circulatory system
transport blood to different
Heart (compact or tubular)
areas of hemocoel
Arteries
Movement of organs and limbs circulates blood
more effectively in open sinuses than heartbeats
and capillaries
 Blood


May contain respiratory
pigments




Hemocyanin (decapods)
hemoglobin
Property of clotting to prevent
loss of blood in injuries
 Excretory
& osmoregulatory organs are paired
glands in head
 Antennal glands/Maxillary glands/green
glands (decapods)- Excretory pores opening @
base of antennae or maxillae
 Some wastes diffuse through gills as well as
excretory glands
 Waste products: ammonia with some urea and
uric acid
 Cerebral



ganglion
Located above esophagus
sends nerves to anterior sense organs
Connect to a subesophageal ganglion by a pair of
connectives around esophagus
 Double
ventral nerve cord has a ganglion in each
segment that sends nerves to viscera, appendages,
& muscles
 Giant fiber systems
 Sensory organs




Eyes
Statocysts- balance organs
Tactile setae (on cuticle)
Chemosensitive setae (on antennae, antennules, &
mouthparts)
 Median



(nauplius) eyes
2-3 pigment cups containing retinal cells
may have lens
Found in nauplius larvae and in some adults
 Compound




eyes
can be on moveable eyestalks (i.e.
crabs/crayfish)
Detect motion, analyze polarized light
Wide visual field due to convex corneal surface
Composed of ommatidia
 Mainly


Barnacles monecious (cross-fertilization)
Parthenogenic in some ostracods
 Most




dioecious
brood their eggs
Branchiopods/barnacles- special brood chamber
Copepods- attached egg sacs to abdominal sides
Malacostracans- carry eggs and young attached to
appendages
Life Cycles


Crayfish juvenile small version of adult
Most produce larvae that must go through series of
changes as it molts


Nauplius- unsegmented body, frontal eye, three pairs of
appendages (2 pairs of antennae & mandibles)
Post-larval forms vary among subphyla
 Class
Branchiopoda
Order Anostraca
 Order Notostraca
 Order Conchostraca
 Order Cladocera

 Class




Maxillopoda
Subclass
Subclass
Subclass
Subclass
Ostracoda
Copepoda
Branchiura
Cirripedia
 Class
Malacostraca
Order Isopoda
 Order Amphipoda
 Order Euphasiacea
 Order Decapoda

 Physics
Features

Reduced 1st antennae

2nd maxillae

Phyllopoda




Flattened, leaf-like legs
Main respiratory organs
Suspension feeding
Locomotion
 Order


Fairy shrimp; brine shrimp
Lack a carapace
 Order





Conchostraca
Clam shrimp (i.e. Lynceus)
Bivalved carapace encloses entire body
 Order

Notostraca
Tadpole shrimp (i.e. Triops)
Carapace forms large dorsal shield covering most trunk
segments
 Order

Anostraca
Cladocera
Water fleas (i.e. Daphnia)
Carapace covers body, but not head
Large portion of freshwater zooplankton
 Physical

Segmented



features:
5 cephalic, 6 thoracic, 4 abdominal
Telson
Maxillopodan eye in the nauplii
 Subclass






Ostracoda
Marine, fresh H2O habitats
Clam-like….bivalved carapace
Several trunk segments fused
# of thoracic appendages reduced to 2 or 0
Burrow in sediments
Scavenge food, feed on detritus, suspension
feeding
 Subclass







Copepoda
Free-living in planktonic & benthic
habitats (marine & fresh)
10 consumer in many aquatic niches
Many symbiotic, some parasitic
Small, elongate, tapered toward posterior
Lacks carapace
Simple, median, nauplius eye
Appendages



4 pairs of flat, biramous, thoracic swimming
appendage
5th pair reduced
No legs on abdomen
 Subclass



Branchiura
Parasitize marine or freshwater fish
5-10 mm long
Physical features:






No gills
Broad, shield-like carapace
Compound eyes
4 biramous thoracic appendages for swimming
Short, unsegmented abdomen
2nd maxillae modified as suction cups
 Subclass




Barnacles
Burrowing or parasitic forms
Enclosed shell of calcareous plates
Sessile as adults


Cirripedia
Some can attach to substrate by a stalk
Physical features:





Carapace (mantle) surrounds body, secretes
calcareous-plated shells
Reduced head
No abdomen
Long thoracic legs
Many-jointed cirri with hair-like setae
 Cirri extend through small opening between
the plates to filter feed
 Largest
class of
Crustacea & diverse
 Marine
& freshwater
 Physical



features:
8 thoracic segments
6 abdominal segments
Each segment has a
pair of appendages
 Order





Isopoda
Asellus- freshwater
Ligia- sea beaches, rocky shores
Porcellio & Armadillidium- terrestrial under stones
or damp places (rollie pollies)
Some parasites of fish or other crustaceans
Physical features:




Dorsoventrally flattened
No carapace
Sessile compound yes
Gills on abdominal appendages
 Order



Amphipoda
Marine and freshwaters
Orchestria- beach fleas
Physical features:




No carapace
Sessile compound eyes
Compressed laterally
gills on thoracic segments
 Order

Important as oceanic plankton- “krill”



Euphausiacea
Uber important in ocean ecosystems
3-6 cm long
Eaten by baleen whales and many fishes
 Order


Decopoda
Lobsters, crayfish, shrimps, crabs
Physical features:



5 pairs of walking legs
First pair of legs modified to form chelae
True crabs have broader carapace & reduced abdomen
 Ura
(fiddler crabs) – burrow in sand
just below high-tide
 Decorator
crabs- cover carapace
with sponges and sea anemones as
camouflage
 Libinia
(hermit crabs)- live in snail
shell; abdomen not protected by
exoskeleton
Centipedes, millipedes
2
tagmata: head & trunk
 One
pair of antennae
 Mandibles
& 2 pairs of maxillae
(1 pair in millipedes)
 Uniramous
legs
 Respiratory
system: respiratory exchange through
body surface and tracheael systems (aquatic
juveniles may have gills)
 Centipedes
 Predators-
earthworms, insects
 Dioecious & oviparous
 Physical features:



Somewhat flattened dorsoventrally
Can have up to 177 segments
Segments bear one pair of appendages



First body segment- modified- venom claws
Head with pair of eyes
Respiration- tracheal tubes with pair of spiracles @
each segment
 Scutigera

15 pairs of legs
 Scolopendra

21 pairs of legs
 “double
footed”
 Millipedes- “thousand feet”
 Herbivorous
 Females lay eggs in nest and guards it
 Physical features



25-100 segments
4 thoracic segments- 1 pair of legs
Abdominal segments



2 pairs of legs on each
2 pairs of spiracles on each
Larva have 1 pair of legs per segment