Phylum Nematoda
Structures: Nematodes also known as roundworms have a worm-like appearance. Their body is long and narrow, resembling a thread. The name nematode comes from the Greek word “nema” which means thread. They have a simple structure of a internal body cavity called a pseudocoelom. They don’t have a very complex body structure.
Body Covering/Support: the skin of the nematode is unusual because it isn’t composed of cells like other animals. Instead of the skin there is a mass of cellular material and nuclei without separate membranes. The skin hides a thick outer cuticle, that is both flexible and tough. However the cuticle is shed as the nematode grows. It is the closest thing the nematode has to a skeleton. The roundworm uses this as a support system and a leverage point for movement. Under the skin lie long muscles, that are aligned longitudinally, that only allow it to move side to side. This way the worm can’t crawl or lift itself. Nutrition/Circulation of Nutrients: The nematodes take their food through a mouth opening into a pharynx where the food is pulled in and crushed. The food is then goes down to the gut where it is digested and not disturbed any vascular system. From here nutrients and wastes are distributed in the body cavity.
Respiration: They have no respiratory system. Instead the nutrients are spread by the excretory canal from the body cavity to each side of the body. Gasses are also diffused through the body cavity. Nervous System: They have an rear nerve ring around the area of the pharynx and two pairs of lengthwise nerve cords that run down the body. There are also dorsal (back) and ventral (belly) nerve cords as well as a set of lateral nerve cords across the body. |
Reproduction: They reproduce sexually. Both females and males possess two tubular gollands. For males the gollands produce the sperm . In females ovaries hold the eggs. During copulation, chitinized spicules move out of the cloaca and are inserted into the genital pores of the female. Then the sperm crawl along the spicule into the female worm. The males are usually smaller than the females. The females can deposit 100,000 eggs per day.
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