They not only look different, they live in different places and eat different food. Observe the preserved arthropods on display. How do the various groups use their legs to walk, swim, feed or mate? Watch the way the millipede moves. Look at the legs. See how the waves of muscle contraction pass down through the segments?
The polychaete worm Nereis moves in exactly the same way. Handle the millipedes very gently. They are someone's pets. They also make great pets for dorm rooms - they need little care, don't take up much room, and don't make noise or messes, unlike your roommate.
Disturb the centipedes to get them moving around. Can you see the poison fangs? Notice how flat the body is, and contrast the number of legs with those of the millipede. Why does each container hold only a single centipede? Don't open the jars unless you have a thing for extreme pain.
Play around with the roly-polys. Oh, go ahead, it's cool. They won't bite. Watch the way they roll up into a ball when disturbed. Not all isopods can do this, but rolling up into an armored ball is a great defensive tactic. Compare our teeny tiny terrestrial version with the enormous preserved marine isopods. Look at the live brine shrimp, hermit crabs and fiddler crabs.
Treat them gently more pets. Watch the way they use their legs, including the modified legs that form their mouthparts. You may see the male fiddler crabs raise their large claw and wave it about to claim a territory inside the tank, in the hopes of attracting a mate Can you blame them? Observe the live crayfish. What does the crayfish do when it feels threatened? How does it use its swimmerets when it is stationary?
Observe the diversity in insect mouthparts etc. Don't worry about being able to identify the individual slides. Try to get a feel for the way modified legs are employed in these animals for a wide variety of sucking, sponging, piercing and biting.
Observe the insects on display. You should be familiar for lab and lecture with the common orders of insects listed in this guide. Crayfish are relatively easy to dissect. Many of you have had ample practice dissecting them at Jazz Fest. Your first task is to determine whether you have a male or female crayfish. Turn the animal on its back, and examine the area of the thorax where the legs join the body.
Female crayfish have a circular opening, like a tiny doughnut, which is their seminal receptacle. Male crayfish have a hardened pair of swimmerets legs on the abdomen that extends back towards the head, and fits neatly into the groove between the walking legs. These modified legs are stiff, like hard plastic. They are curved like half a soda straw, and when they are joined together, they make a tiny tube through which the sperm travel during copulation. Crayfish literally copulate with their legs.
Observe their external anatomy. Identify the following structures: rostrum, antennae, eyes, thorax, carapace, chelae claws , cheliped, walking legs, abdomen, swimmerets, telson, and uropod. Examine the various appendages and modified appendages closely. Note that some are biramous ex. The uniramous appendages result from the evolutionary loss of the second branch. Arthropods exist today because they have successfully adapted to changing environments during this long period of time.
Although arthropods are everywhere, we do not know how the different groups are related. Scientists have proposed many conflicting ideas about how arthropods evolved and diversified. Researchers at the Australian Museum have been studying the relationships between groups of arthropods.
They have attempted to resolve the problems of arthropod phylogeny by re-examining available information using new technology and by studying some recently discovered Cambrian fossils. The new technology used by the researchers included: DNA sequencing, electron microscopy and computer-aided phylogenetic analysis. The Australian Museum is in a unique position to tackle the problem of arthropod phylogeny because it has specialists in all major groups of arthropods.
Three pairs of thoracic legs. Wings present or absent. Class Insecta. Two distinct body regions head and trunk. One pair of legs per trunk segment. Two pairs of legs per trunk segment. Class Crustacea crus-ta-ce-uh , the crustaceans. This is a very diverse class.
Its members display much variation in the tagmata and the appendages. There are about 30, species of Crustacea. Most are aquatic, the majority of which are marine. Crustaceans includes lobsters, crabs, crayfish, shrimp, barnacles, and several less familiar forms. One of the latter is the Isopoda, the sowbugs and pillbugs or roly-polys. Most people will likely encounter only two orders, the Orders Decapoda and Isopoda.
Order Decapoda dec-o-po-da. Lobsters, crayfish, crabs, shrimp. Two tagmata cephlothorax and abdomen. Two pairs of antennae can be difficult to see both pairs Five pairs of legs on the cephlothorax, the first pair usually with a large claw.
Order Isopoda eye-so-po-da. Sowbugs, pillbugs, roly-polys. Three tagmata head, thorax and abdomen. Two pairs of antennae: first pair is greatly reduced , seldom noticed. Seven pairs of legs , one pair on each thoracic segment. Abdomen small, more or less fused. Most isopods are marine, living in seaweed and under stones in the water. There are a few freshwater forms. The only Crustacea to invade the land are the isopods However, they have not severed all ties with the aquatic habitat for they are only found in places of high moisture.
This includes places such as leaf litter and soil and beneath bark and stones. A few are occasionally pests of cultivated plants, but they usually feed on organic debris.
Those that can roll into a ball are called pillbugs or roly-polys; those that can not form a ball are the sowbugs. Class Arachnida uh-rak-nid-uh , spiders, ticks, mites, scorpions and others. This is a diverse class which belongs to a subphylum of the Arthropoda known as the Chelicerata.
Chelicerata are characterized as having two distinct body regions, a cephlothorax and an abdomen. Chelicerates have six pairs of appendages, the first two pairs being mouthparts and the following four pairs being legs. They do not have antennae. The first pair of mouthparts are the chelicerae sing. They are three-segmented and pincher-like.
In spiders, the terminal third segment is often called a fang. The second pair of mouthparts are the six-segmented pedipalps. They may appear leg-like spiders or claw-like scorpions. The legs of most Chelicerata have seven segments. The undescribed species of insects in the United States, however, is estimated at some 73, The largest numbers of described species in the U.
Several enlightening studies have been conducted involving the numbers of individual insects in a given area. In North Carolina, soil samples to a depth of 5 inches yielded a calculation that there were approximately million animals per acre, of which 90 million were mites, 28 million were springtails, and 4. A similar study in Pennsylvania yielded figures of million animals per acre, with million mites, million springtails, and 11 million other arthropods.
Even specific insect species have been found to be quite numerous, with calculations of from 3 to 25 million per acre for wireworms larvae of click beetles. Certain social insects have large numbers in their nests. An ant nest in Jamaica was calculated to include , individuals.
A South American termite nest was found to have 3 million individuals. Locust swarms are said to hold up to one billion individuals.
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