Phylum Arthropoda (Insects, spiders & crustaceans)

Appearance Symmetry: bilateral Segmentation Jointed appendages: modified for walking, feeding, sensory, copulation & defense Hard exoskeleton made up of protein and a flexible substance called chitin. The chitin is coated with a waxy layer making the exoskeleton water proof.

The exoskeleton Advantages Disadvantages Protects arthropods like a coat of armour Provides support for muscles and internal organs Disadvantages A hard external exoskeleton that is non-living and therefore cannot grow with the animal. Heavy and restricts the size of the arthropod

Exoskeleton Exoskeleton is secreted by the underlying epidermis and shed at intervals This process is called moulting and allows the animal to continue to grow. A newly moulting Cicada (right)

Circulation Open circulatory system with a well developed heart. Blood is pumped through the body sinuses and eventually collects in a large cavity near the heart, called a hemoceol, where it re enters the heart. Hemoceol Heart Artery

Movement Well developed muscles coordinated by the nervous system Move by contracting muscles which are attached to the exoskeleton

Feeding Herbivors, carnivores, filter feeders, detritus feeders Appendages are adapted to specialized mouthparts used for feeding siphon

Respiration Gills (crustaceans) Book gills/book lungs (spiders) Feathery gills Book gills/book lungs (spiders) Several sheets of tissue layered like the pages in a book This increase surface area to volume ratio Tracheal tubes (insects) Long tubes that reach deep into tissue where O2 diffusion takes place Connects to the air via spiracles

Nervous System Very well developed nervous system Can smell, taste and see – compound eyes can detect motion extremely well

Nervous System Brain = a pair of ganglia that acts like a central switch board for incoming information From the brain, a nerve cord runs along the ventral part of the body. Along the nerve cord there are more ganglia which serve as a command center for the specific segments

Excretion Solid waste exits via the anus Nitrogenous wastes In Aquatic arthropods – excreted through the green gland near the base of the antennae In spiders – Malphighian tubules –removes nitrogenous wastes from blood and adds it to undigested food

Reproduction Dioecious Fertilization usually takes place inside the body of the female In spiders and some crustaceans, males deposit a sperm packet Insects and most crustacean males have a special reproductive organ to deposit sperm inside the female

Complete Metamorphosis Egg hatches into a larva that looks nothing like the adult As the larva grows it moults Larva sheds it skin and becomes a pupa – the insects body is rearranged This occurs in a protective cocoon. Adult insect emerges from cocoon as complete adult

Incomplete Metamorphosis Egg hatches into a miniature adult but with no functioning sex organs At this stage the insect is called a nymph As is grows it moults as it gets bigger At this stage the insect is called a juvenile Along the way the insects acquires adult characteristics

Ecological and Economical Importance Plants depend on them for pollination Many symbiotic relationships Ex. Fish/cleaner shrimp Aid in agriculture Silk production Pollination Eat harmful species (ladybugs eat aphids) Can also damage crops (locust) and transmit diseases (mosquitoes)

Three Subphylums Chelicerae Crustacea Uniramia Spiders, horseshoe crabs and scorpions Crustacea Crayfish, fleas, crabs, barnacles Uniramia Insects, centipedes, millipedes Using your textbook, research the differences among these subphyla.

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