Download Ch 38 Arthropoda

Ch 38 –
Phylum Arthropoda
Characteristics of Arthropods
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Segmented (Arthropod means “jointed foot”
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Body segments have jointed appendages
Exoskeleton
Provides protection and support
 Made of 3 layers excreted by the epidermis
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Outer layer – waxy, mix of proteins and lipids
– Repels water and prevents dessication
Middle layer – primary protection, protein and chitin
 Inner layer – flexible at joints, protein and chitin
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– Muscles attach to move body segments
Characteristics Cont’d
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True Coelom
Bilateral symmetry
Cephalization
Variety of appendages around mouth
 Most have segmented antennae at anterior
 Compound eyes
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Made of many individual light detectors
 Sense light intensity
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– Send impulses to brain, then move along ventral nerve cord
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Open circulatory system
Molting
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B/c of exoskeleton, arthropods can’t grow
without periodically shedding
In between molts:
Tissues swell to put pressure on exoskeleton
 Hormone is released
 Epidermis secretes enzymes to digest inner layer
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Uses this material to build new exoskeleton
Outer layer loosens and breaks
Molting Cont’d
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Takes days for new exoskeleton to become
hard
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Very vulnerable during this time
Evolution and Classification
¾ of all animal species belong to this phylum
 Extremely diverse
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Lobsters, crabs, spiders, centipedes, insects, etc.
First appeared more than 600 mya
 Various groups have undergone evolutionary
changes
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Scientists still believe they had a common ancestor
Ancestor: body segments identical, Living species:
Specialized tagmata
Evolution and Classification Cont’d
Divided in 4 subphyla
 Trilobita (extinct animals called trilobites)
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Crustacea - Lobsters, crabs, crayfish, etc.
 Have pair of chewing mouthparts - mandibles
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Chelicerata – spiders, scorpions, ticks, etc.
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No antennae, pincerlike mouthparts - chelicerae
Uniramia – centipedes, millipedes, insects
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Have antennae and mandibles, appendages are
unbranched
38-2 Subphylum Crustacea
Characteristics
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2 pairs of
appendages on
head – feelers
Each other body
segment generally
has a pair of
appendages
 Some are branched
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Characteristics Cont’d
Exoskeletons contain large amounts of CaCO3
 Gas exchange
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Some through exoskeleton, some gills
Development
Most have free-swimming larva called a nauplius
 3 pair appendages, 1 eye
 Takes adult form through series of molts
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Characteristics - Size
Large range, but mostly small
 Small
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Copepods and Water fleas
 Size of a comma
 Copepods = ocean plankton
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Large
Japanese Spider Crab
 14 foot leg span
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The Crayfish
Freshwater relative of lobster
 Decapod = 5 pairs of legs
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External Structure
Body divided into 2 main parts
 Cephalothorax
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Consists of 2 tagmata
Head – 5 segments
 Thorax – 8 segments, posterior to head
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Dorsal exoskeleton fused into the carapace
Abdomen
Lies posterior to cephalothorax, 7 segments
 7th is called the telson, forms flat paddle
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External Structure Cont’d
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Pair of app. attached to each segment
(except telson) See chart pg. 749
Antennules and Antennae: feelers sensitive to
touch, taste
 Mandible: Chews food
 Maxilla: 2 pairs, manipulate food, assist with
respiration
 Maxillipeds: 3 pairs, manipulate food, sensitive to
touch and taste
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External Structure Cont’d
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Chelipeds: Most anterior on thorax, end in large
pincers
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Walking leg: 4 pairs, movement over solid surface
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First two pairs end in small pincers for grasping
Swimmeret: attached to five abdominal segments
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For capturing food and defense
Create water currents and used in reproduction
Uropod: On sixth abdominal segment, used for
propulsion
Crayfish Ventral View
Crayfish - Digestion
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Food passes through esophagus to
stomach
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Stomach grinds food into fine paste
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Uses teeth made of chitin and CaCO3
Paste mixed with enzymes excreted by a
digestive gland
 Moves through intestine (further digestion
and absorption)
 Waste leaves body via anus
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Crayfish –
Respiration
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Use gills
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Extend from base of each walking leg into
chamber under carapace
Legs circulate water across gills during
walking
 Posterior pair of maxillae as well
 Each gill covered by extension of
exoskeleton
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Thin enough for gas exchange
Crayfish - Circulation
Excess water eliminated through organs called
green glands
 Open circulatory system
 Dorsal heart
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Pumps hemolymph through vessels
Hemolymph enters hemocoel, bathing tissues
Passes through gills for gas exchange
Returns to heart
Crayfish – Nervous system
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Brain (pair of ganglia) located above
esophagus
Receives impulses from eyes, antennae, antennules
 Nerves extend down to control mouth appendages
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Ventral nerve cord runs posteriorly
38-3 Subphylum - Chelicerata
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Class Arachnida
Class: Arachnida
Includes spiders, scorpions, mites, & ticks
 Body is divided into cephalothorax and
abdomen (similar to crayfish)
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Cephalothorax usually includes:
 6 pairs jointed appendages
 1 pair chelicerae (picher-like mouthparts)
 1 pair pedipalps
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Aid in holding food and chewing
4 pairs of walking legs
Spider Anatomy
Body is pinched b/t cephalothorax and
abdomen
 Chelicerae modified as fangs used to inject
venom
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Venom produced by poison glands in the CT
 Flows through ducts in chelicerae to tips
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Most have 8 simple eyes
Spider Anatomy cont’d
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Posterior tip of abdomen has 3 pairs of organs
called spinnerets
Each made of hundreds of microscopic tubes
 Connect to silk glands in abdomen
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Fluid made from protein hardens into threads as it is
pulled from the spinnerets
Used to spin webs, build nests, protect eggs
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Some move to a new habitat by allowing wind to
pull their threads
Spider Anatomy Cont’d
Nervous, digestive, circulatory systems all
very similar to crustaceans
 Respiratory system is different (terrestrial!)
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Book lungs: paired sacs in the abdomen with
many folds for gas exhange
And/or
 Tracheae: system of tubes that carry air directly to
tissues
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Through openings in exoskeleton called spiracles
Spider Anatomy Cont’d
Excretory system – modified for land
 Malpighian tubules: hollow projections of
digestive tract
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Collect body fluids and waste, carry to intestine
 Most water reabsorbed, wastes leave body in
solid form
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Coxal glands
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Organs that remove wastes and discharge them
through openings at the base of some legs
Life of a Spider
Feed mostly on insects, some can catch fish
frogs, or birds
 Many predator adaptations
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Chase, Trapdoor, Snare
Male usually smaller than female
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As soon a sperm is transferred to female, the
male moves away quickly
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May get eaten if he isn’t fast enough
Female then puts fertilized eggs in silken case
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Carries it or attaches it to something
Life of a Spider Cont’d
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Most venom harmless to humans
only 2 fatal species in U.S.
 Black Widow
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Red/orange hourglass shaped mark ventral abdomen
 Venom attacks nervous system
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Brown Recluse
Violin shaped mark on dorsal cephalothorax
 Venom digests tissues surrounding the bite
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Scorpions
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Differ from spiders in 2 ways
Large pincerlike pedipalps
 Large stinger on the last abdomen segment
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Curled over body
Usually nocturnal hunters
 Prefer tropical or desert climates
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chelicerae
eyes
pedipalp
Mites and Ticks
Completely fused CT and abdomen
 Mites
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Most less than 1 mm in length
 Both free living and parasitic
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Ticks
Range from a few mm to over an inch
 Many parasitic
 Can transmit Rocky Mountain Spotted Fever and
Lyme disease
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Mite and Tick Body Regions
pedipalps &
chelicerae
cephalothorax
abdomen
American dog tick male
Blacklegged (deer) tick female
American dog tick female laying egg mass (1000-2000 eggs!).
Subphylum –
Uniramia
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Myriapods
Could have been first animals to appear on land
 Highly segmented
 Little variation to appendages
 No waxy exoskeleton
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Live in damp environment
Class –
Diplopoda
Millipedes
 2 pairs of legs per segment
 Adapted for burrowing through soil
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Move slowly (legs are short)
Rounded bodies
 Eat plant matter
 Short antennae, 2 groups simple eyes
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Bad vision, good sense of smell
Class –
Chilopoda
Centipedes
 15-175 pairs of legs
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1 pair per segment
Can be very large in tropical regions
 Flattened bodies
 1st segment app. modified as poison claws
 Predatory
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Move quickly in search of prey (earthworms,
insects, etc.)