Crabs of the British Isles (29,193 t), various swimming crabs (3,180 t), the spider crab "Maja squinado" (1,565 t), the shore crab or green crab "Carcinus maenas" (553 t) and the velvet crab "Necora puber" (193 t). Around 77% of the catch is landed in the United Kingdom, 19% in Ireland, 4% in the Channel Islands, and 1% in the Isle of Man. 62 species have been directly observed in the waters of the British Isles: Three deep-water species have also been recorded near the British Isles, and are likely to occur in the area. These are: Crabs of the British Isles Around 65 species
British Isles also taken to be part of the British Isles, even though, as islands off the coast of France, they do not form part of the archipelago. The oldest rocks in the group are in the north west of Scotland, Ireland and North Wales and are 2.7 billion years old. During the Silurian period the north-western regions collided with the south-east, which had been part of a separate continental landmass. The topography of the islands is modest in scale by global standards. Ben Nevis rises to an elevation of only , and Lough Neagh, which is notably larger than other lakes