Trinchesia caerulea (Montagu, 1804)

1 July, 2016.
Lephinchapel, Loch Fyne on the west coast.
15 mm animal at 14 metres. Water temperature 10C.
Sony α6000  in Nauticam housing, Zeiss 50 mm macro lens and 2 x Inon D-2000 flashes.