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 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 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.