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ARTHROPODS
Phylum Arthropoda
General Characteristics
 Triploblastic
and have bilateral
symmetry
 Protostomes
 Metameric body plan
 Chitinous exoskeleton
 Paired, jointed appendages
 Growth
accompanied by molting
 Ventral
nervous system with fused ganglia
 Coelom
reduced to cavities surrounding the
gonads
 Open
circulatory system
 Complete
digestive tract (mouth and anus)
 Metamorphosis
often present
Why are arthropods so successful?
 1.
Metameric body plan: body is divided
into segments which are specialized for
feeding, sensory perception, locomotion
and visceral functions.
 2.
Exoskeleton: provides support and
protection, prevents water loss and
allows for the attachment of muscles.
The Exoskeleton

A. Molting (shedding of the exoskeleton)is necessary for
growth.

B. Divided into four stages

Enzymes begin digesting the procuticle (the inside layer
of the exoskeleton)

New exoskeleton is secreted

Old exoskeleton splits when animal stretches by air or
water intake

Calcium carbonate deposits harden the new exoskeleton.
Metamorphosis

3. Metamorphosis: a radical change in body form
and physiology as an immature stage becomes an
adult.

A. Complete: egglarva  pupa  adult

B. Incomplete egg  nymph  adult

C. Reduces competition between adults and
immature stages.
Class Arachnida:

Examples : spiders, ticks, mites and scorpions

A. First pair of appendages (called chelicerae) are pincerlike

B. Digestion: inject prey with digestive enzymes and suck up
the partially digested animal tissue with a pharynx, water
reabsorption done in the hindgut (intestine)

C. Have two body segments: Prosoma and opisthosoma

D. Respiration: book lungs (resemble the pages of a closed
book).
Other systems of Arachnids

E. Excretion: Malpighian tubules absorb
nitrogenous waste from the blood and empty it into
the digestive tract.
 F. Nervous: have a variety of mechanoreceptors and
chemoreceptors called sensilla, do not have
antennae but do have compound eyes to detect
movement.
 G. Reproduction: dioecious, male transfers sperm
to female in packages, oviparous (lay eggs outside
the body) although some scorpions are
ovoviviparous (eggs are laid internally)
Subphylum Uniramia:

Examples : insects

A. Have uniramous appendages

B. Three body segments: Head, thorax and abdomen

C. Locomotion: insects walk, run, jump, swim or fly (first
animals to fly)

Direct or synchronous flight (muscles move the wings)

Indirect or asynchronous flight (muscles move the
exoskeleton causing the wings to move.)

D. Digestion: Have an upper lip and a lower lip,
mandible and maxillae, esophagus, crop, gastric
cecae (digestive gland), intestine, rectum, anus

E. Respiration: Tracheal tubes (a highly branched
network of tubes open to the outside through
spiracles.)
 F.
Excretion: Malpighian tubules
 G. Nervous: single pair of antennae,
use chemoreceptors and
mechanoreceptors, have compound
eyes, some have Johnston’s organ at
the base of the antennae for sensing
vibrations, some insects are capable of
learning and memory
H.
Reproduction: mating behaviors
may include visual signals,
auditory signal or pheromones,
dioecious and oviparous,
fertilized eggs are deposited by
the ovipositor.
Subphylum Crustacea
 Examples
: crayfish, shrimp, lobsters, and
crabs.
 A.
Have biramous appendages (shaped like a
Y)
 B.
Two body segments: Cephalothorax and
abdomen
 C.
The exoskeleton of the cephalothorax is the
carapace.
Other systems- Crustaceans
 D.
Digestion: Mandibles (chewing and
grinding), maxillae (food handling), esophagus,
stomach, digestive gland, intestine, anus
 E.
Respiration: gills attached to the walking
legs
 F.
Excretion: Green glands located at the base
of the antennae eliminate nitrogenous waste

G. Nervous: Two pair of antennae and
compound eyes on eyestalks, statocysts
(balance), chemoreceptors and tactile setae.
 H.
Reproduction: dioecious , male deposits
sperm near the females gonoducts, fertilized
eggs attach to the swimmerets.