{Biology 112

Arthropods and Echinoderms

Includes animals such as crabs, spiders, and insects

Segmented bodies, a tough exoskeleton (external body covering) and jointed appendages (legs and antennae that extend from the body wall)

Fewer body segments than worms and highly specialized appendages used for feeding, movement and other functions

Most only have 2-3 segments Appendages include walking legs,

antennae, wings and mouthparts

Anthropods

Herbivores, carnivores and omnivores

Most receive gases through a network of tracheal tubes that extend throughout body Openings are called spiracles

Others have book lungs Aquatic organisms have gills Eliminate wastes through

structures called Malpighian tubules

internal fertilization (terrestrial) and external for aquaticFunctions of

Arthropods

Body Structure

Arthropods and Exoskeleton

Arthropods outgrow their skeletons and molt

The entire skeleton is shed and manufactures a larger one to take its place

Groups of Arthropods

Classification is based on number of segments and appendages – particularly mouthparts

Crustaceans (Crustacea)

Chelicerates (Chelicerata)

Uniramians (Uniramia)

Crustaceans

Crabs, shrimp, lobster, crayfish, barnacles

Two pairs of antennae, 2-3 body segments (head, thorax and abdomen), chewing mouthparts called mandibles

Chelicerates

Horseshoe crabs, spiders, ticks, and scorpions

Have mouthparts called chelicerae and 2 body segments

Four pairs of walking legs

Spiders spin webs of silk

Uniramians

Centipedes, millipeds and insects

Have jaws, one pair of antennae, unbranched appendages

Most body segments have one pair of legs each

Three body parts – head, thorax and abdomen Three pairs of legs attached to the thorax Usually, a pair of antennae, a pair of compound eyes,

and two pairs of wings Can detect changes in colour and movement Three pairs of appendages used for mouthparts Growth usually involves metamorphosis, the process of

changing shape and form Some are harmful to humans and others helpful The communicate using sound, chemical and other types

of signals Some are also capable of forming societies

Insects

Sea stars, sea urchins, and sand dollars Characterized by spiny skin, a water

vascular system, and suction-like structures called tube feet

Have an endoskeleton, five part radial symmetry as adults and are all deuterosomes

Contain a water vascular system that is filled with fluid that carries out much of its life functions

A maldreporite

Echinoderms