Roundworms

aka the Nematoda Class

ORGANIZATION

The nematodes or roundworms comprise the phylum Nematoda. They are a diverse animal phylum inhabiting alot of environments. Nematode species can be difficult to distinguish; and although over 28,000 have been described, of which over 16,000 are parasitic, the total number of nematode species has been estimated to be about 1 million. Unlike cnidarians and flatworms, nematodes have tubular digestive systems with openings at both ends.


http://en.wikipedia.org/wiki/Nematode


GERM LAYERS

It is made up of three layers. The endoderm, mesoderm and the ectoderm.


SYMMETRY

The type of symmetry that roundworms have is bilateral. They have a body that is cylindrical. Most of these species are parasitic on plants and animals.


Big image

CEPHALIZATION

Roundworms have nerve bundles on one end, but no optical receptors, making them less cephalized than flatworms.


BODY CAVITY

Roundworms are pseudocoelomates; while they have a body cavity, it is not composed of mesodermal epithelium and is thus not a true coelom.


SEGMENTATION

No segmentation.


DIGESTIVE SYSTEM

A roundworm has a definite 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.


Big image

NERVOUS SYSTEM

A roundworm has two nerve cords that transmit impulses in the roundworm.


Big image

CIRCULATORY SYSTEM

No circulatory system.


RESPIRATORY SYSTEM

No 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.


Big image

REPRODUCTION

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 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.


SUPPORT

They have small bristles, known as setae, which are sensing devices that can identify any soil. Roundworms only move laterally. Roundworms use their long muscles and move by thrashing themselves through their environment.