Tardigrades

Tardigrades have barrel-shaped bodies with four pairs of stubby legs. Most range from 0.3 to 0.5 millimetre (0.012 to 0.020 in) in length, although the largest species may reach 1.2 millimetres (0.047 in). The body has four segments (not counting the head), four pairs of legs without joints, and feet with four to eight claws each. The cuticle contains chitin and is moulted periodically.
Tardigrades are eutelic, with all adult tardigrades of the same species having the same number of cells. Some tardigrade species have as many as about 40,000 cells in each adult's body, others have far fewer.
The body cavity consists of a haemocoel, but the only place where a true coelom can be found is around the gonad. There are no respiratory organs, with gas exchange able to occur across the whole of the body. Some tardigrades have three tubular glands associated with the rectum; these may be excretory organs similar to the Malpighian tubules of arthropods, although the details remain unclear.