Speaking of beasts in bilges, 15yr ago I had a wooden Harkers snapper boat, abt 33'. Leaky old thing, built in 1960. I was "down there" cleaning out bilge by reaching between stringers and ribs scraping out paint chips, oily gunk, gunk in general.
And something BIT MY HAND!!!
Talk about backing up fast out of the hole!!
Turns out it was a stone crab, juvenile.
Apparently in the fall I was running crab traps, and this little bugger made it out of the trap and out of view and into the bilge. This was spring so the critter spent all winter in the bilge.
He was healthy and apparently well fed. On what, well it's a 40yr old leaky wood boat. Smorgasbord, I guess. Was repatriated.
Just keep this in mind when you reach into dark places down there!!