What Kind of Excretory System Does a Fluke Worm Have?

Basic Anatomy

• Flatworms, the family to which flukes belong, are thought to be descendents of an early type of jellyfish. They have three layers of cells. The outer layer is a covering known as the ectoderm, and the endoderm forms the lining of the digestive system. Between the endoderm and the ectoderm is a layer of cells known as the mesoderm. Flukes have a leaf-like shape and an outer cover known as the tegument. This outer layer can be spiny or smooth. Trematodes have two attachment organs, also known as suckers.

Digestive Waste

• The digestive system of flatworms consists of a gut that is much like a sac. Food enters through the mouth and is digested in the sac and whatever is not digested exits again through the mouth. Trematodes have this basic system with a mouth that extends into a pharynx which leads to the oesophagus and ends in the caeca or sac-like gut. The process of allowing waste to be removed via the mouth is known as egestion or regurgitation and is necessary because the trematodes have no anus.

Excretory System

• The most important way that Trematodes get rid of waste products is through the well developed excretory system. The system, which is protonephridial, consists of flame cells which are linked to tubules that open into ducts that end in the bladder. The bladder develops as the young adult matures. This part of the excretory system is primarily involved with osmoregulation. There is either a single pore or a pair of pores that open directly from the bladder to excrete waste. Waste is also excreted through the tegument or outer layer of the trematode. The epithelium that lines the fluke's digestive tract also absorbs material.

Life Cycle

• Of the many types of flukes that cause disease in humans, the schistosomes are most common, infecting an estimated quarter of a billion people around the world. These flukes require an intermediate host as part of their life cycle and their first port of call is a snail. Each type of fluke has a specific snail that it must burrow into. It is in this intermediate host that it reproduces and multiple larvae leave the snail and look for human skin into which they will burrow. The larvae then surf through the blood of the human host and find their way to the intestinal linings where they reproduce and lay eggs. The eggs are excreted from the host and so the cycle begins again.