[3] Mystacocarids occur along the coasts of South and North America, southern Africa, and the western Mediterranean.

[2] Mystacocarids are tiny pigmentless crustaceans, less than 1 mm (0.039 in) long, that live in the spaces between sand grains on intertidal beaches.

The head is relatively large and divided into two by a stricture, so that the larger posterior part gives the appearance of being the thorax.

The pair on the first segment has been modified into maxillipeds, which collaborates with the maxillae in the feeding process, but is not fused with the head.

Their limbless abdomen ends in a supra-anal plate, a telson and a pair of large, pincer-like furca which on the ventral surface bears two sets of combs with setae.