Pachyotoma crassicauda is a distinctive but scarce species that is found in wet habitats such as the margins of lakes and ponds, the sea shore, and Sphagnum bogs. It is black or dark violet in colour and reaches a maximum length of 1.5 mm. The eyes have 8+8 ocelli and the surface of the body has a 'granulated' appearance. The furca is long and the dens has numerous dorsal and ventral setae (Fig. 1). The manubrium has 2+2 apical ventral setae and the mucro is about a fifth of the length of the dens.