ARTHROPODS Phylum Arthropoda
Jan 03, 2016
ARTHROPODS Phylum Arthropoda
General CharacteristicsTriploblastic and have bilateral
symmetryProtostomesMetameric body planChitinous exoskeleton Paired, jointed appendages
Growth accompanied by moltingVentral nervous system with fused
gangliaCoelom reduced to cavities surrounding
the gonadsOpen circulatory systemComplete 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: egglarva 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
pincer-like 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 tubulesG. 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.