Level of Organization

Roundworms have organs but they do not have organ systems.

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Germ Layers

Roundworms contain all three germ layers: endoderm, mesoderm, ectoderm.


A roundworm has bilateral symmetry.


A roundworm has cephalization because they have a head that the body follows.

Body Cavity

The roundworm has a pseudocoel body cavity.


The roundworm is not segmented.

Digestive System

A roundworm has a digestive system that runs the length of their bodies. It has a mouth, pharynx, intestine and anus. Many are parasites and live off other animals and plants.

Circulatory System

A roundworm has no heart or formal blood vessels.

Respiratory System

A roundworm has no formal respiratory system.

Excretory System

A roundworm has an anus at its rear end and a series of excretory tubes that end in an excretory pore.

Nervous System

A roundworm has two nerve cords that transmit impulses.


A roundworm reproduces sexually. The female has an ovary, holds eggs in an oviduct and then passes them to the uterus, where they are fertilized. The male has sperm cells that are made in the testis and stored in the vas deferens. When it is time to reproduce, the sperm cells pass through the spicule. Over 200,000 eggs can be deposited at once in the soil once they are fertilized.


A roundworm has no skeleton, but they have muscles to flip and move.