Ivell’s sea anemone (Edwardsia ivelli) is the only know endemic animal to be known to have gone extinct (probably) in Britain in modern times. It has not been found since 1983 despite detailed searches at its only known site, Widewater Lagoon in West Sussex.
From Few and Far Between: On The Trail of Britain’s Rarest Animals by Charlie Elder. An excellent and amusing read,
“It was the summer of 1972, and Oxford zoology graduate Richard Ivell had risen early, eager to press on with his research. He stepped into his backyard to sort through several buckets of mud and brine collected the day before. These thick, stinking sections of sediment dug from Widewater Lagoon in West Sussex provided raw material for his master’s thesis on the ecology of brackish environments. Sandwiched between land and open sea, lagoons are vulnerable and yet hostile habitats, where fluctuating temperature and salinity test life forms to the limit. Landlocked Widewater, a shallow stretch of water running for nearly a mile next to the A259 near Worthing, provided the perfect place to study. Bordered by the back gardens of houses to the north and beach huts to the south, the narrow basin is kept topped up by rainfall and by the sea that percolates through its shingle banks during high tides. Various kinds of prawns and cockles live within its confines, and some of these creatures would have been scooped up in the samples Richard had collected just a couple of metres out from the seaward edge. The mud had settled overnight within the buckets, each surface a dark brown disc submerged under a lens of clear salt water. In the quiet, life had stirred.
Forty years later, the memory is still vivid, as Professor Ivell told me on the phone from the animal biology institute in Germany where he now works. Peering over the rim of one of the containers, he couldn’t believe what he saw. ‘In the stillness, small anemones had emerged and their lightly banded tentacles were spread out flat against the sediment. The thing I remember is how beautiful they were, and how fragile, like tiny flowers in a desert. It was quite amazing to see.’Unable to identify the small burrowing species, he showed a colleague at Oxford University, Richard Manuel. If the catchphrase among Anthozoa taxonomists is ‘know thine anemone’, then Dick was the person to ask. An expert in such marine life, he realised that these specimens, no more than a couple of centimetres long, buff coloured with twelve transparent tentacles, the outer nine marked with cream bands, were new to science.”