The first pair of appendages are usually modified as antennae. Crustaceans have two pair of antennae. Another set of anterior appendages are modified as mandibles, which function in grasping, biting, and chewing food. Male crayfish also use one pair of legs as a copulatory organ. All crustaceans share a common type of larva called a nauplius larva.
They are one of the few successful terrestrial crustaceans. They feed on decaying vegetation in the leaf litter. Uniramians have a single pair of antennae, and uniramous appendages.
They probably evolved from oligochaete worms. Class Chilopoda - 2, sp. Centipedes dwell in damp places under old logs and stones. They are carnivorous, eating mostly insects. They are highly segmented, and have one pair of legs per segment. The first trunk segment bears poison fangs.
Centipedes are very dangerous, and their bite is extremely painful. Class Diplopoda - 10, sp. Millipedes share the same habitat as centipedes, but they are mostly herbivorous, feeding on decaying vegetation in the leaf litter. Animals that feed on detritus are called detritivores.
Each segment of the millipede is actually two segments fused together hence the double set of legs. They can secrete a defensive fluid that smells bad, and a few species actually secrete tiny amounts of cyanide gas to protect themselves! Class Insecta - , sp. If we knew all the different insects on Earth, there could be as many as 30 million species.
Insects evolved about mya, with cockroaches and dragonflies among the first to appear. Insects have a head, thorax, and abdomen, with three pair of legs 6 legs on the thorax. Crustaceans have legs on the abdomen as well as on the thorax. Most insects have one or two pairs of wings. They are the only invertebrates that fly. Most have compound eyes , and can communicate by sound and scent, using powerful chemical hormones called pheromones.
Insects have extremely elaborate mouthparts, consisting of pairs of appendages fused into a lower lip labium , and an upper lip labrum , with other appendages called maxillae aiding in chewing. These mouthparts are highly modified in various groups for chewing, sucking, and piercing.
Insects undergo metamorphosis as they develop, changing from one form to another as they mature. The juvenile stages look like tiny versions of the adults. Their larvae are often radically different from the mature adult like the butterfly and the caterpillar. 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. In the United States, the number of described species is approximately 91, 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. These great numbers of insect species and individuals were created by a number of factors including their long geological history, the capability of flight, their small size that allows survival in many various habitats, their ability to store sperm for delayed fertilization, and their general adaptive abilities to the environment.
Insects have remarkable fertility and reproductive abilities, which have usually led to the vast numbers of individuals in nature. East African termite queens have been recorded to lay an egg every two seconds, amounting to 43, eggs each day. Arthropods are divided into four major groups:. Get our monthly emails for amazing animals, research insights and museum events. Arthropods have been around for a long time. Their ancestors originated million years ago in Cambrian oceans - at a time that is still only incompletely understood.
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.
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