Nematoda
Nematodes, commonly known as roundworms, are characterized by having bodies that do not have lines that section the body into segments, called non-segmented bodies, as well as having exoskeletons that envelop its body that the nematode sheds and regrows regularly. This exoskeleton acts as protecttion from harmful elements of the worm's environment. The head of the nematode is rounder than the tail. Because nematodes lack a circulatory system, nematodes have a digestive system and a cavity in the body called the pseudocoelom that contains fluid that delivers nutrients throughout the body of the nematode.
Nematodes live in a variety of habitats, including land and aquatic. The majority of species of nemtodes live in moist, damp soil, so many species that one square yard of soil can hold hundreds of different types of nematodes and around one million individual worms. Nematodes that live in soil habitats can reside in fields, forests, beaches, and and grasslands, as well as other habitats with moist soil. Aquatic species of nematodes can live in the bottom of lakes, oceans, and other bodies of water, as well as in plant and animal tissues and animal body fluids.
Nematodes have papillae, structures that enable the worm's sense of touch. The structures are miniscule and cover the entirety of the nematode's body, consisting of structures that resemble nipples as well as small sensory hairs. Nematodes sense chemicals in its environment through chemoreceptors called amphids, which look like tiny cavities on each side of the back of the worm's head. Nemtodes usually do not posses eyes, but some do, in which case they are located in the nematode's throat.
Nematodes are invertebrates. They need cannot control their own body temperature so the internal temperature of the worms is controlled by their environment. Because their temperature depends on their environment, nematodes are called thermoconformers. Nematodes must be able to withstand both low and high temperatures in order to survive, so they either avoid climates with extreme temperatures or they adapt to the temperature of their habitat.
Since nematodes live in damp environments, it is imperitive to their survival that their cells remain in an isotonic solution, meaning that the amount of water moves in and out of cells at a constant rate so that the amount of water inside and outside the cells remains the same. Hypotonic and hypertonic environments can cause a nematode to die. In a hypotonic environment, too much water inside of the cells can result in the cells bursting, and in a hypertonic environment, cells do not have enough water in them shrivel up and die. Nematodes use osmoregulation to maintain an equal ration of water inside of the cell to water outside of the cell, resulting in the cells remaining in an isotonic environment.
Nematodes do not posses a respiratory or a circulatory system, so they distribute oxygen throughout their body by means of the fluid in the pseudocoelom. The worms take in oxygen from water and soil in their environment and produce an output of carbon dioxide.
Different types of nemtodes feed in different ways. Herbivores feed on plant roots, bacteriavores feed on bacteria, and some species are predators to oter nematodes. Once a nematode eats its food, it is begins the process of digestion, where the moleculs of the food are broken down and converted to energy called ATP. Nematodes have a complete digestive system, which is divided into three parts. The three parts, the stomodeum, intestine, and proctodeum, are another thing that classify nematodes. The stomodeum consists of the worm's mouth, lips, gums, and cheeks. The lips, gums, and cheeks are part of the buccal cavity. Some species of parasitic nematodes have a buccal cavity that is shaped in a way that allows the worm to punture the host cells and take in material from those cells. The stomodeum also includes the pharynx, a pump that moves food into the nematode's intestine. After the food molecules are broken down and digested, the worm absorbs the sugars from the broken-down molecules and proceed to expel the remaining food waste from the digestive tract. Waste is also removed by diffusion, as the worm takes in oxygen through its skin and diffusing the metabolic waste out of its body.
Nematodes have a compartment under their skeletons that contain a fluid that is under pressure. The nematode can control its movements because the worm's muscles allow the shape of the compartment to change. This type of skeleton is called a hydrostatic skeleton.
Nematodes reproduce sexually, though some are hermaphrodites, meaning that they have both male and female reproductive organs and produce both sperm and eggs, and can undergo self-fertilizatoin. Femal nematodes are larger than the males, and possess a reproductive structures of ovaries, seminal receptacles, a uteri, ovijector, and vuvla. They have either one or two ovaries, and can deliver up to 1,000 fertilized eggs in one day. The reproductive structures of males include one testis, a seminal vesicle, and a vas deferens. It takes a couple of days for a nematode to devlop from a zygote to an adult.
