Hyloniscus riparius (C. Koch, 1838)
The pygmy woodlice of family Trichoniscidae (and Styloniscidae) are readily distinguished from other woodlice by the shape of the antennal fagellum which comprises a tapered cone (of indistinct segments) bearing a terminal bristle.
Hyloniscus riparius looks very similar to, and easily overlooked as, Trichoniscus pusillus agg. It is slightly larger and darker in colour, and has the eye comprising a single ommatidium (as seen in Oritoniscus flavus). In Trichoniscus spp. there are 3 ommatidia.
It is not included in the current identification guides (AIDGAP & Linnean Synopsis) and will erroneously key to Oritoniscus flavus. A brief description with figures is given by Gregory & Farmer (2023).
Specimens of this central European species were found beside the river Avon in Worcestershire in April 2022. Further field work has discovered a handful of additional sites along a several kilometer length of the river.
Specimens of Hyloniscus riparius have been found under riverside flood debris, mainly comprising dead wood. At all sites it is associated with Trachelipus rathkii.
This is a central European woodlouse, characteristic of riverside flood plains, but it is also readily spread by human activity (such as the horticutural trade) and in recent decades it has rapidly spread into north west Europe, notably The Netherlands and Belgium.
This account is based on Gregory & Farmer (2023).