This is pretty random since it's done out of boredome.
My inspiration i would say would be "Jules Verne"

You can see a little Aztac relic on the bottom left.
and a warrior's helmet. The helmet is fairly new i guess since there
isn't much alge growth on top of it. The Seaman is holding an Air Pressure
harpoon thrower and has a 3 barrel gun in the right side on his suit.
The sea creature has a giant shell on it's back -- not so clearly visible from
this angle. it has the abdomen and limbs of an Insect. the head of a reptile.
with 4 eyes on each side of the head --- and a long tail that resembles an eel.
it has a horn on the front of it's head and 2 other ones on the sides of it's mouth.
From all these horns i'd say it's a pretty agressive animal. but i wouldn't give up
hope for the Seaman. He's going to give the creature a battle before he dies.
maybe he'll even kill the creature and take it into his submarine to study this
new species.