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Arthropods
Phylum Arthropoda
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Greek for jointed feet
Crabs, shrimp, barnacles,
Insects, spiders etc.
Largest phylum of animals
with ~ 1 million known
species
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Of all the animals on earth,
3 out of 4 are arthropods
Have a tremendous ability
to take advantage of just
about every habitat.
Phylum Arthropoda
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Evolution of exoskeleton
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Composed of chitin
• Tough, rigid material allows for
great protection and support
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Causes limitation in size
• In order to grow the arthropod
must molt its exoskeleton
• You wont see an arthropod as
big as a squid or a whale
• Right after molting arthropods
are at their most vulnerable
state
Phylum Arthropoda
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Bilaterally symmetrical
Coelomate
Segmented Body
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Divided into 3 segments:
head, thorax and abdomen
Evolution of jointed
appendages
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Increased mobility / flexibility
(legs)
Modified for feeding and
senses (mouthparts)
Used for protection
Arthropod Biology
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Digestion
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Filter feeding, scavengers, predators
Appendages closest to the mouth, such as the
maxillipeds, are specialized to sort out food and
push it toward the mouth.
2 chambered stomach that has chitinous teeth or
ridges for grinding and bristles for sifting.
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Open Circulatory System
 Respiratory System
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Arthropods have developed 3 types of respiratory
structures depending on their environment gills,
tracheae, or book lungs
Arthropod Biology
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Acute Senses
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Many produce pheromones (a chemical odor) in
order to communicate and have highly developed
senses
Most have one pair of large compound eyes and 3
to 8 simple eyes
• A simple eye – is a visual structure with only one lens
that is used for detecting light
• A compound eye – is a visual structure with many
lenses. Each lens registers light from a tiny portion of
the field of view
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Reproduction
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Separate sexes with internal fertilization
Arthropod Biology
 Niche
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(What they do / their role):
Arthropods are of great direct and indirect importance to
humans
The larger crustaceans--shrimps, lobsters, and crabs--are
used as food throughout the world
• Small planktonic crustaceans, such
as copepods, water fleas, and krill,
are a major link in the food chain
• Approximately two-thirds of all
flowering plants (angiosperm) are
pollinated by insects
• They function as decomposers
Arthropods are major carriers of
disease
Phylum Arthropoda
3 Subphylums
Chelicerates
2. Crustaceans
3. Uniramia
1.
Subphylum Chelicerates
General Characteristics:
 Chelicerates have six pairs of
appendages, which are uniramous
(unbranched)
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include a pair of chelicerae, a pair of
pedipalps, and four pairs of walking legs
 Lack
mandibles and antennae
 Respiration is by means of book gills, book
lungs, or tracheae.
Subphylum Chelicerates
3 classes:
1.
2.
3.
Merostomata - horseshoe crabs
Pycnogonida - sea spiders
Arachnida - spiders, ticks, mites
Class Merostomata
 Horseshoe
Crabs
• Carapace covering body
• Cephalothorax, abdomen, telson
• 6 pairs of appendages
• Research using blood
1. Class Merostomata
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two different groups of marine organisms
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Members of this class have a large shield that covers the
cephalothorax.
The compound eyes are reduced
The second pair of appendages, the pedipalps, resemble
walking legs.
They have a long, spike-like appendage called a telson that
projects from the rear of their bodies.
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the eurypterids and the horseshoe crabs
Eurypterids are now extinct (they lived 200 to 500 million years ago)
Horseshoe crabs feed on small invertebrates
The horseshoe crab uses its telson to flip itself over if it got flipped on
its back. It is not used for defense as one might suspect.
Respiration is via book gills.
1. Class Merostomata
2. Class Pycnogonida
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An example is a sea spider
Sea spiders appear to be a sort of marine "spider,"
approximately 1000 described species – all are marine
They feed by sucking juices from soft-bodied
invertebrates through a long proboscis.
The body itself is not divisible into neatly- organized
tagmata or regions as it is in most other arthropods.
An anterior region bears, besides the proboscis, three or
four pairs of appendages, including the first pair of
walking legs.
2. Class Pycnogonida
3. Class Arachnida
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Spiders, ticks, mites, scorpions
over 60,000 described species – spiders make
up the majority of those known species
They have 8 legs instead of 6 like insects have
Nearly all species are terrestrial
Respiration is via tracheae or book lungs
They have a two-segment body, made up
merely of the thorax and abdomen.
The pedipalpi (leg-like mouthparts) of some
species has instead been adapted for sensory,
prey capture or reproductive functions.
3. Class Arachnida
 Arachnids
are mostly carnivorous, feeding
on the pre-digested bodies of insects and
other small animals.
 Many are venomous - they secrete poison
from specialized glands to kill prey or
enemies.
 Others are parasites, some of which are
carriers of disease.
Arachnids
Subphylum Crustacea
 Barnacles,
crabs,
shrimp, etc.
 Head, thorax,
abdomen
 Specialized
appendages-antennae, mandibles,
maxillae
Class Malacostraca
Order Decapoda
5
Pairs of walking legs
 Crabs, shrimp, lobsters
 Krill—importance to
food chain
 Unique pattern of
segmentation among
crabs
Class Cirripedia
 Barnacles
 Filter
feeders
 Sessile (including on other living
organisms)
 Feathery appendages (legs) to filter food
 Larvae swim then attach for
metamorphosis
Class Copepoda
 Copepods
 Important
plankton
 Filter feeders
 Stay afloat by enlarged appendages
 Many parasitic