Philoscia affinis Verhoeff, 1908
Philoscia affinis is superficially similar to the ubquitous P. muscorum in general appearance. The pigmentation of the head and body is a good indicator for field identification, but reliable identification requires microscopic examination of 7th pereiopod of a male specimen.
A brief description, with figures, is given by Gregory (2020).
The presence of Philoscia affinis in the UK was first confirmed in south-east England in summer 2017 (Segers, Boeraeve & De Smedt, 2018).
Subsequently, specimens previously mis-identified as P. muscorum collected in 2004 in South Wales and in 2006 from Oban, western Scotland were re-identified as Philoscia affinis. Recent field work has discovered many additional sites, mainly in western Britain, including North Wales (Hughes, 2019), and in Northern Ireland (Anderson, 2019). This species has clearly been over-looked in Britain and Ireland and could prove to be widespread if searched for.
Philoscia affinis has a preference for rural sites, such as open woodland and rank coastal grassland (in contrast P. muscorum generally favours open grassland sites). It does not favour synathropic sites such as churchyards and gardens (in which P. muscorum thrives). However, there are a few recent records (BMIG Newsletter 47, 2023, pg 8 & 11) from garden centres and a city centre raised ornamental street planter suggesting that it may be spreading further afield via the horticultural trade.
It can be found under stones and dead wood, or among accumulations of leaf-litter.
This summary is based on Gregory, 2020.