Flatworms are exactly what they are called, they are a flat worm, very thin and look like a small leaf. They are an unsegmented flat worm with a head and a tail end.

These worms are normally around 1/2" or 20 mm to 2" or 50 mm in length.

The bilateral (affecting two sides) shape of the body ( both ends are the same) is an important feature because it permits the concentration of sensory structures and nervous function in the head end.

One very important fact that I found out years ago is that they have no body cavity other than their gut. They also do not have a anus, and therefore the same opening is used to takes in food and expels waste.

The respiratory system and blood system on flatworms are also completely missing and therefore, diffusion (penetrate through pores) is used for transport of oxygen inside the body. This is one reason why flatworms are flat.

These worms are fairly common through out New Zealand, and the rest of the world. They live on the bottom in shallow water. Around rock pools I have sometimes seen one or two darkish coloured ones and sometimes the brightly coloured ones thet you can find in slightly deeper water.

Flatworms are generally plain bland colours though some found have bright coloured stripes or markings on them making them quite unique. I beleive that their brilliant colour patterns much like nudibranches have evolved entirely for defense against predators, mainly fish.

Like with many other colourfull animals eg: some frogs, this bright colouration is often associated with the presence of a distasteful toxic or poisonous defense substances that warn potential predators that the flatworm is full of distasteful chemicals and not worth attempting to eat. . Therefore, we can assume that conspicuous colours are mostly associated with the presence of a toxic and bad tasting compounds.