The Nematoda consists of species of roundworms and are very abundant and can be found almost everywhere. In fact, you can find nearly a million individual Nematodes in a square yard of soil! It is very hard to detremine the species Nematodes because of how indifferent they all are. They are either larger or smaller, some microscopic. Nematodes are characterized by an external (outer) layer of cuticle, a strong and flexible noncellular layer, that is secreted by the hypodermis below it. The Nematode does not have a coelom, instead, they have a pseudocoel formed directly from the cavity of the blastula. Pseudocoel aids in the circulatory system because Nematodes don't have one. The nervous system is basically anterior nervous tissue that covers the pharynx which forms dorsal and ventral nerve chords from one end to the other.
Nematoda digestive system
The digestive system in Nematodes is complete and is divided into three separate parts, these parts inlcude the stomodeum, intestine, and proctodeum. The stomodeum contains the buccal cavity and esophagus and it is lined with the cuticle. The proctodeum is also lined with the cuticle. Lastly, the intestine stretches from the esophagus to the proctodeum and is a simple, tubelike structure. The digestive system works when food is secreted by different enzymes found in the glands in the esophogus. Afterwards, it is then sent through the esophagus to the intestine.
The Ascaris Lumbricoides is the biggest of the roundworms and is the most common parasitic worm in humans. It is common in tropical and subtropical countries and is responsible for the disease ascariasis. It's digestive system is not fully developed and has a one-way digestive system from the mouth to the anus. They also have a cavity between their digestive tract and their body wall which is called psuedocoel.
Ancylostoma duodenale (hookworm)
The Ancylostoma duodenaleis parasitic and lives inside the small intestine of humans and other mammals such as dogs. Their digestive system works by taking in food or even blood from the hooks the hookworm has. The food then travels through the Pharynx and into the intestine without the use of a coelum cavity. To force the food down, it uses forces other than it's own. Lastly, the food is then released though the anus.
Trichuris Trichiura (whipworm)
Whipworms are parasitic roundworms that have a tail shaped as a whip and also lives in the small intestine of mammals such as humans and dogs. The whipworm starts it's digestion system process by consuming food where it breaks down into the digestive tract where it leaves through the mouth since the mouth is the only hole in the whipworm. The whipworm is very different than others. This is because it's digestive system takes place in its head which means it can't absorb food through the skin like the hookworm.