Phylum Arthropoda (jointed foot) Arthropods Page 715

Arthropods are classified based on the number of body segments they have and the appendages attached to these segments. Arachnids (spiders, scorpions and ticks) Crustaceans (lobster, crabs, barnacles, krill, crayfish) Centipedes and millipedes Insects (bugs, grasshoppers, flies, bees, ants)

First appeared in the sea over 600 million years ago. First arthropods had many body segments. Some have evolved to have just two or three.

Major characteristics of Arthropods? – Jointed appendages (structures that extend from the body---legs, antennae) – Segmented bodies – Exoskeleton made of protein and chitin

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Why must an arthropod molt its exoskeleton?

You are a molting arthropod… What would you be doing? Where would you be?

Form and function in arthropods Feeding: omnivores, herbivores and carnivores with a variety of suitable adaptations. Respiration: Most terrestrial arthropods breath through a network of branching tracheal tubes that are throughout the body. Air enters and leaves the tracheal tubes through small openings called spiracles. Spiders have book lungs- layers of respiratory tissue stacked like a book. Most aquatic arthropods have gills.

How gills work CUk CUk

Circulation – Open circulatory system. Well- developed heart that pumps blood through vessels. Blood leaves vessels and moves through cavities. Finally collects in a large sinus surrounding the heart, re-enters the heart and is pumped around again.

Excretion: Most terrestrial arthropods dispose of nitrogenous wastes using Malpighian tubules- saclike organs that extract waste from the blood and add them to feces. Cellular waste of aquatic arthropods is released directly into the water.

Response: Well-developed nervous system with a brain and sophisticated sense organs (ie. compound eyes) Movement: Well-developed muscle systems controlled by the nervous system. (see diagram page 718)

Reproduction: Terrestrial: internal fertilization Aquatic: external fertilization – females release eggs and then males release sperm over them.

Arachnids

2 segments 4 pairs of appendages

Spin webs made of silk using their spinnerets which are located near the back of their abdomens.

Also use silk to wrap prey and baby spiders sometimes use it as a balloon to float away.

Some spiders chase their prey. First set of appendages have poison (fangs!)

CentipedeMillipede

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