Adineta ricciae

Adineta ricciae is a microscopic invertebrate that can grow to a length of about 0.2 millimetres (0.008 in). It has a retractable head with two pigmented, front-facing eyes, a mouth aperture and a corona of cilia. The bands of cilia are used in locomotion with two separate groups twirling in opposite directions. The body is slightly broader than the head and is cylindrical and contains the internal organs. It has muscles, a large stomach and short intestine, a cloaca, an excretory system, nerve ganglia, organs sensitive to touch and a pair of ovaries. At the posterior end is a foot with foot glands, short triangular spurs and three toes. The whole is enclosed in a flexible, transparent cuticle.

Bdelloid rotifers are aquatic organisms and when their habitat dries up, they have the capability of going into a dormant state known as cryptobiosis to survive desiccation. They can remain in this state for periods of several years and when circumstances improve, they can revitalise in a few hours and continue with their normal activities. No male bdelloid rotifers have ever been found and it is believed that all bdelloid rotifers reproduce solely by means of asexual reproduction through the process of parthenogenesis. Molecular studies have shown that all bdelloid rotifers are descended from a common ancestor which lost its ability to reproduce sexually about 80 million years ago. Adineta ricciae has been used in this research.