Nematoda

Dalton Elleman

Level of Organization

They have an organ system.

Germ Layers

They're triploblastic meaning they have three germ layers. They are: mesoderm, endoderm, and ectoderm.


Symmetry

They have bilateral symmetry.


Body Cavity

Well-defined and large pseudocoelom.

Digestive System

There is no stomach, with the pharynx connecting directly to a muscleless intestine that forms the main length of the gut. This produces further enzymes, and also absorbs nutrients through its single cell thick lining. The last portion of the intestine is lined by cuticle, forming a rectum, which expels waste through the anus just below and in front of the tip of the tail. Movement of food through the digestive system is the result of body movements of the worm. The intestine has valves or sphincters at either end to help control the movement of food through the body.


Circulatory System

They have no circulatory system.


Excretory System

In many marine nematodes, one or two unicellular 'renette glands' excrete salt through a pore on the underside of the animal, close to the pharynx. In most other nematodes, these specialised cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct. This transverse duct opens into a common canal that runs to the excretory pore.


Segmentation

Nematodes have no segmentation.


Nervous System

The bodies of nematodes are covered in numerous sensory bristles and papillae that together provide a sense of touch. Behind the sensory bristles on the head lie two small pits, or 'amphids'. These are well supplied with nerve cells, and are probably chemoreception organs. A few aquatic nematodes possess what appear to be pigmented eye-spots, but is unclear whether or not these are actually sensory in nature.


Reproduction

Most nematode species are dioecious, with separate male and female individuals. Both sexes possess one or two tubular gonads. In males, the sperm are produced at the end of the gonad, and migrate along its length as they mature. The testes each open into a relatively wide sperm duct and then into a glandular and muscular ejaculatory duct associated with the cloaca. In females, the ovaries each open into an oviduct and then a glandular uterus. The uteri both open into a common vagina, usually located in the middle of the ventral surface.


Support

Nematoda are supported by a hydrostatic skeleton.


Sources

Course Notes - Platyhelminthes, Nematoda


Wikipedia - Nematode


DIVERSITY OF LIFE - SYNOPTIC DESCRIPTION OF THE PHYLUM NEMATODA