There are several recent records of T. testudinalis from Carlingford Lough, about 95 km north of Bray where it occurred in the 19th century. There are no recent, reliable Irish records further south but many further north such as that at top left at St John’s Point, Killough, Northern Ireland 54.23° N © N. Nolan.
A decline and apparent ‘loss of species from south of Isle of Man’ was observed when none was found in the years 2000 – 2005 where it had previously been found intertidally in the1970s and early 1980s (Hawkins in Mieszkowska, 2005), but it was present recently, at least sublittorally as shown at bottom left, and right from the southern tip of Isle of Man, 54.05° N (2014) © P. Lightfoot, and Niarbyl, 54.16° N (2017) © D. Kipling.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig