Order Acari - 30, sp. Most are very tiny, less than 1 mm long. The thorax and head are fused into a single unit cephalothorax. Order Opiliones 5, sp. It has an oval body with extremely long legs, which they frequently lose in various accidents and brushes with predators.
They are predators, herbivores, and scavengers. Look at them closely next time you see one. They carry their eyes atop a little tower on their back weird! Crustaceans are mostly marine, and dominate the ocean to the same degree that insects dominate the land and air.
Despite their aquatic diversity, there are very few terrestrial crustaceans, just as there are very few truly aquatic insects. Crustaceans have biramous appendages. Each leg has an additional process, like a little miniature leg branching off from the main leg.
Many groups of crustaceans have lost this extra appendage during subsequent evolution. The Order Decapoda have five pair of walking legs, and include the familiar crabs, lobsters, and crayfish. 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. 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. 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. Compared to insects, whose legs have six segments, there is an extra segment, called the patella, between the third segment the femur and the fourth segment the tibia. Common orders of Arachnida include:. Order Araneae a-ran-e-uh , the spiders. No antennae. Abdomen joined to cephlothorax by slender pedicel. Four pairs of legs. Mouthparts: One pair chelicerae and one pair of pedipalps.
Eyes simple ocelli. Usually eight, sometimes fewer. Poison apparatus opens on the fangs of the chelicerae. Silk apparatus always present at end of abdomen, below anus. This is a large order, having about species in North America. Although nearly all spiders have venom glands, spiders seldom bite man. Only a few U. In Nebraska, the black widow and the brown recluse are the only seriously venomous spiders. Order Acari ak-a-ri , the mites and ticks.
Abdomen broadly joined to cephlothorax no pedicel. Four pairs of legs in adults; only three pairs at hatching. Ticks and mites occur just about anywhere animal life is found. They may be terrestrial or aquatic, free-living or parasitic. They may feed on organic debris beneficial scavengers or on living plants or animals. Some of the plant feeders are serious pests of crops. Some of the parasitic forms are pests of animals and man. Some are vectors of diseases. A few of the predatory and parasitic mites are considered beneficial because they feed on insects or other pests.
Over 30, species of ticks and mites have been described. Order Scorpiones scor-pi-on-es , the scorpions. No pedicel between cephlothorax and abdomen. Four pairs of legs on cephlothorax. One pair of chelicerae and one pair of long, pincher-like pedipalpsAbdomen with seven broad segments anteriorly, followed by five narrower segments which end with a large stinger. Scorpions feed mostly on insects and spiders which they catch with their pedipalps. They may or may not sting their prey.
Scorpions do not ordinarily attack man, but they will sting if disturbed or cornered. Of the forty-some species that occur in the U. One Arizona species, however, is very venomous, and its sting can be fatal. Class Chilopoda chi-lo-po-da , the centipedes. Two tagmata head and trunk One pair of antennae with 14 or more segments. Mouthparts: one pair of mandibles and two pairs of maxillae. Appendages on the first trunk segment are clawlike poison jaws or fangs with which centipedes paralyze their prey.
The class name refers to the lip- like appearance of the fused bases of these appendages. Eyes may be present or absent.
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