This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Ikuchi (Japanese)
The ikuchi is an extremely long fish dwelling in the deep waters off Hitachi Province (now Ibaraki Prefecture). It has only been spotted at night, sometimes rearing out of water and slinking over a ship, taking a long time to complete its passage, and leaving a residue of viscous oil. The sheer amount of oil needs to be dumped overboard lest the ship may sink.
When an ikuchi’s path crosses a boat’s, the sea monster envelopes the boat in its tentacle-like body. It slithers over the sides and across the deck, slowly sliding its whole body over the boat. Ikuchi are so long—many kilometers, by some accounts that it can take hours for an entire one to slither over a boat. On a few occasions, boats have been tangled up in this monster for days.