The Capillaria Nematode (Capillaria pterophylli) is a freshwater aquatic parasitic roundworm in the Trichosomoididae family of nematodes. It is found in and attached to Goldfish and other freshwater fish. It is a disease in the fish, and eventually kills the fish. It is a capillarid. 

The Capillaria Nematode is very small and difficult to see. It is transparent (clear or see-through). It is long and cyclindrical like a worm (but not flat like a flatworm). It is smooth. It has a thorny head at one end. 

It is found in the body of the Goldfish, usually in the intestine, but it can also be found in the muscle, liver, and other tissues. The fish is called a host. The Capillaria Nematode can spread from one fish to another fish, when a big fish eats an infected fish. 

The life cycle is egg, larva, and adult.

The female Capillaria Nematode is oviparous. She lays thick-shelled eggs. The eggs hatch after about 21 days. 

Location of photographs: Paris, France

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM