CRUSTACEA > MALACOSTRACA > ISOPODA > Oniscidea > Synocheta > Trichonisidae

Trichoniscus pusillus and Trichoniscus provisorius are considered to be morphologically identical although the former is slightly larger and, whilst it is possible to distinguish males by microscopic examination of the first exopod, it is common practice to treat both species as an aggregate. This means that, strictly speaking, the taxonomic name used here should be either Trichoniscus pusillus/provisorius or simply Trichoniscus pusillus agg. 

Both forms have a distinctive reddish or purple-brown colour with a smooth body surface and stepped transition between the pereion and pleon. They have eyes comprised of three ommatidia, and tapered antennal flagella as previously described. Trichoniscus pusillus may reach 4mm long, possibly slightly larger in gravid females. Trichoniscus provisorius rarely exceeds 3.5mm.

The problems associated with separating these species has resulted in under-recording but, even so, they are recognised as being very common and widespread. Despite the lack of records, independent research has shown that Trichoniscus pusillus is better suited to cooler and damper areas, whereas Trichoniscus provisorius is more likely to be found in sunnier and/or dryer locations. Habitat can be varied with both species found relatively close to the soil surface, typically on the underside of stones and deadwood or within leaf-litter. Unlike Haplophthalmus danicus, this species will move rapidly when disturbed which, once again, makes them a difficult species to photograph in a natural setting.

All of the individuals featured below were photographed in damp woodland habitat under deadwood, so are very likely to be Trichoniscus pusillus.