Halophiloscia couchii is a fast and agile woodlouse reminiscent in the field of an immature Ligia oceanica, but the stepped body outline and three flagella segments (very elongated) are characteristic of H. couchii (L. oceanica has numerous bead-like segments).
Halophiloscia couchii occurs widely along the southern and western coastlines of England and Wales, around the Channel Islands, but just a few records from eastern Ireland.
It is typically associated with unvegetated rocky cliffs, boulder beaches or shingle beaches, rarely far above the supralittoral zone.
By day it occupies dark, humid and inaccessible crevices and can be extremely difficult to locate. It is most easily found by turning boulders on storm terraces or at the base of rocky sea cliffs, but rapidly seeks shelter when disturbed. On rocky cliffs it typically occurs with Ligia oceanica.
This summary is based on the detailed account in Gregory (2009).
Gregory, S. (2009) Woodlice and Waterlice (Isopoda: Oniscidea & Asellota) in Britain and Ireland. Field Studies Council/Centre for Ecology & Hydrology.
World List of Marine, Freshwater and Terrestrial Isopod Crustaceans: https://www.marinespecies.org/isopoda/aphia.php?p=taxdetails&id=146965
