Those apart of the Nematoda phylum are known as nematodes or roundworms. There are over 15,000 known species of roundworms, which live in various different environments. Nematodes are bilaterally symmetrical. Roundworms can be either free living or parasitic. These organisms play a significant role in the environment, as they decompose soil organic matter, as well as mineralization of plant nutrients. These organisms have the capability of growing to up to 50 centimeters long.
MOVEMENT: Nematodes move by using their lengthy muscles. These organisms have high internal body pressure when these muscles contract. This causes the nematode to flex, creating a back and forth motion when they move, thus pushing these organisms forward.
BODY COVERINGS: Nematodes normally have two to three distinguishable cell layers. Below the epidermis, there is a layer of lengthy muscle cells. In order to protect themselves, nematodes have a cell that releases a substance that is meant to slow predators down. These organisms have the organ system level of organization meaning that groups of two or more tissue work together to make an organism function.
SUPPORT: Nematodes can be cylinder-shaped, spindle-shaped, pear-shaped, or lemon-shaped and they are unsegmented. These organisms are invertebrates, and they maintain their body shapes with their cuticle.
NUTRITION: Nematodes simply obtain their prey through their mouth, commonly feeding on plants, algae, and sometimes even other nematodes. Parasitic roundworms however feed on their hosts.
RESPIRATION: Nematode respiration is done through diffusion. This means that gas molecules within the nematodes would move from move from an area of higher concentration into an area of lower concentration.
CIRCULATION: Since these organisms lack a circulatory system, nematodes have a pseudocoelom, which is a body cavity that maintains body fluids.
EXCRETION: A nematode has a mouth at the front of its body where food is taken in, and an anus at the end of its body where the waste is released. These organisms have a network of excretory tubes which are meant to transport solid waste to the anus of the nematodes.
RESPONSE: These organisms have sensory organs that help them respond. Nematodes have brains that help them detect predators, prey, and even mates. As well, bodies are covered with sensory hairs and papillae, which provide the nematodes with a sense of touch. On the organism's head, there are small cavities. The small cavities work as chemoreceptors which is a sensory organ that detects chemicals. Lastly, nematodes have four main nerves. The dorsal nerve controls nematodes muscle movement, and extends down the back of the organism. The lateral nerves transmit sensory information to the brain, and run along either side of the nematode. The ventral nerve assists with both motor control and sensory input, and is located on the underside of the roundworm.
REPRODUCTION: Nematodes reproduce sexually. While most nematodes have either male or female reproductive organs, making them dioecious, some species have both reproductive organs making them hermaphroditic. When dioecious species reproduce, the male roundworm will have a specialized spine that is used to open a female roundworm’s reproductive tract. Once opened, the male will then inject sperm into the female. Some species are live-bearing, meaning that the baby nematode will simply come out of the female nematode as is. Other species will lay eggs, which will be released from gonopore which is a hole in the middle of a female’s body. Once the eggs hatch, the baby nematode will be just like an adult, however they will not have their reproductive organs until fully developed. Hermaphroditic nematodes reproduce by self fertilization, meaning they would not have to find a mate.