Form And Function In Arthropods

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Jul 20th, 2012
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Arthropods use complex organ systems to carry out different essential functions. Some of these organs are found only in this phylum. Most arthropods use tracheal tubes or other specialized organs for respiration, have an open circulatory system, and excrete wastes through saclike tubules.

Feeding Arthropods include herbivores, carnivores, and omnivores. There are arthropod bloodsuckers, filter feeders, detritivores, and parasites. Arthropod mouthparts have evolved in ways that enable different species to eat almost any food you can imagine. Their mouthparts range from pincers or fangs to sickle-shaped jaws that can cut through the tissues of captured prey.

Respiration You can see a grasshopper’s internal organs, including those used for respiration, in Figure 28-4. Like all terrestrial animals, grasshoppers need a way of obtaining oxygen from air rather than from water. Most terrestrial arthropods breathe through a network of branching tracheal (TRAY-kee-ul) tubes that extend throughout the body. Air enters and leaves the tracheal tubes through spiracles (SPEER-uh-kulz), which are small openings located along the side of the body. Other terrestrial arthropods, such as spiders, respire using book lungs. Book lungs are organs that have layers of respiratory tissue stacked like the pages of a book. Most aquatic arthropods, such as lobsters and crabs, respire through featherlike gills. The horseshoe crabs, however, respire through organs called book gills.

Circulation Arthropods have an open circulatory system. A well-developed heart pumps blood through arteries that branch and enter the tissues. Blood leaves the blood vessels and moves through sinuses, or cavities. The blood then collects in a large sinus surrounding the heart. From there, it re-enters the heart and is again pumped through the body.

Excretion Most terrestrial arthropods, such as insects and spiders, dispose of nitrogenous wastes using Malpighian (mal-PIG-ee-un) tubules. Malpighian tubules are saclike organs that extract wastes from the blood and then add them to feces, or digestive wastes, that move through the gut. In aquatic arthropods, diffusion moves cellular wastes from the arthropod’s body into the surrounding water.

Response Most arthropods have a well-developed nervous system. All arthropods have a brain. The brain serves as a central switchboard that receives incoming information and then sends outgoing instructions to muscles, Two nerves that encircle the esophagus connect the brain to a ventral nerve cord. Along this nerve cord are several ganglia, or groups of nerve cells. These ganglia coordinate the movements of individual legs and wings. Most arthropods have sophisticated sense organs, such as eyes and taste receptors, for gathering information from the environment.

Movement Arthropods move using well-developed groups of muscles that are coordinated and controlled by the nervous system. These muscles generate force by contracting and then pulling on the exoskeleton. At each body joint, different muscles either flex (bend) or extend (straighten) the joint. The pull of muscles against the exoskeleton allows arthropods to beat their wings against the air to fly, push their legs against the ground to walk, or beat their flippers against the water to swim.

Reproduction Terrestrial arthropods have internal fertilization. In some species, males have a reproductive organ that places sperm inside females. In other species, the males deposit a sperm packet that is picked up by the females. Aquatic arthropods may have internal or external fertilization. External fertilization takes place outside the female’s body. It occurs when females release eggs into the external environment and males shed sperm around the eggs.

Reference : Prentice Hall Biology

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