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. Note that each pair of antennae are biramous appendages.
Examine the telson and uropod. How does the crayfish use these biramous appendages to escape predators? Using a probe, try to find the mouth and anus. Note the thick triangular mandibles , a primary trait of crustaceans.
Place the crayfish in the pan with its dorsal side up. Carefully cut the carapace just to one side of the midline with your scissors, and down along both sides. Peel it back to expose the gills. Notice how the gills interface with the legs, and observe the second underlying row of gills. Cut away the gills where they join the body. Try to find the tiny heart good luck! Just under the heart are the gonads ovaries or testes. The evolution of many types of appendages—antennae, claws, wings, and mouthparts— allowed arthropods to occupy nearly every niche and habitat on earth.
For hundreds of millions of years, animals lived only in the oceans. Then, about million years ago, fossil tracks suggest that an arthropod left the water to walk on land.
Arthropods invaded land many times. Fossil evidence shows that different groups including insects, millipedes and centipedes, spiders, and scorpions all came ashore on their own at different times. Some groups, such as crabs and barnacles, secrete calcium carbonate into the exoskeleton, making it thick and hard. To grow, arthropods must molt shed their exoskeletons periodically. During the molt, they form a larger exoskeleton to allow for expansion.
The combination of an exoskeleton and jointed appendages is analogous to a suit of armor. The muscles for movement are attached to the inner surface of the exoskeleton Fig. Vertebrates such as fish and humans have an internal skeleton, called an endoskeleton , with muscles attached to its outer surface Fig. In species like millipedes and centipedes, the segments are quite similar to each other Fig. In other species, like an ant, the segments are clustered in major body regions.
Insects have an abdomen of several segments and a separate head and separate thorax Fig. Most segments have a pair of attached jointed appendages. The posterior pairs commonly function as swimming legs swimmerets , the middle pairs as walking legs, and the anterior pairs as food-getting apparatuses chelicerae , or maxillae and mandibles or sensory organs antennae. Arthropods have a complete digestive system and a true coelom. Arthropods have a nervous system with a large ventral nerve cord that branches into many smaller nerve fibers that innervate the body.
The ventral nerve cord leads to a small brain in the cephalic or head segment of the body. Many arthropods have image forming compound eyes and excellent chemosensory abilities.
The circulatory system of arthropods is open, as it is in molluscs. While vessels carry blood from the heart into the body cavity, blood returns into the heart through small pores.
Another special feature among arthropods relates to their musculature. While most invertebrate musculature is of the smooth type similar to the muscles lining the digestive tract of humans , arthropod muscles are primarily striated like the skeletal muscles of humans.
Striated muscle has a much faster contraction rate than smooth muscle, and it is this feature that probably enabled the development of flight in many insects. Arthropods are generally dioecious meaning they have two separate sexes , and in many species development is indirect , which means that the immature form is a larva that appears very different from the parent and undergoes a process called metamorphosis to change to the adult body plan.
The caterpillar to butterfly transformation of the lepidopteran insects is a dramatic example of this type of life cycle. Chelicerata from the Greek word chela meaning claw is the subphylum of arthropods that includes spiders, mites, scorpions, and horseshoe crabs.
Unlike other arthropods, chelicerates lack antennae. They also do not have the mandible food processing appendages used by other arthropods for tearing and grinding food.
They instead possess a set of clawed appendages called chelicerae that are used to grab and shred food. Most chelicerates are terrestrial; exceptions are the sea spiders and the horseshoe crabs.
Not to be confused with true crabs, horseshoe crabs have their head and thorax segments are fused into a single segment called the cephalothorax that is covered by a carapace , an unjointed piece of exoskeleton Fig. This region of the body contains the walking legs and chelicerae. The abdomen segment of the horseshoe crab has the reproductive appendages and five paired gill flaps, each of which contains approximately book gills , used for gas exchange.
The book gills are named because they are arranged like the pages in a book. Horseshoe crabs are considered living fossils because modern horseshoe crabs are similar to those appearing as fossils from million years ago.
Sea spiders are known as pycnogonids pycno - means closely packed and gonid refers to gonidia, which is a group of asexually reproductive cells. Sea spiders are in the class Pycnogonida. Arthropods are traditionally divided into 5 subphyla: Trilobitomorpha Trilobites , Chelicerata, Crustacea, Myriapoda, and Hexapoda. Terrestrial arthropods insects and their relatives, such as spiders, scorpions, and mites are the most successful and diverse forms of multicellular life on Earth.
In this course we cover of basic principles of their biology, including their structure and function, development, ecology, behavior and reproduction.
Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home What makes arthropods so successful? Ben Davis May 31, What makes arthropods so successful? What are the factors responsible for the success of arthropods on land? What are 5 characteristics of arthropods? What three characteristics can you list for the arthropods? What is unique about arthropods? What is the largest group of arthropods? What is the biggest group of invertebrates?
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