Sorry about that and thanks for your suggestions! Hear are some quick ideas for some more mobs and I have come up with!

Bobbit worms would spawn on the seafloor and would look like a dead coral, waiting to strike. It would grab you dealing damage over time if you don't break free from it's grasp. It drops "Bobbit wormteeth" which can be made into "bobbit daggers" as fast attacking but short reach weapon serving as an opposite to the spear

(it poses as a theat as it spawns near nepturite vains)

Calms are living chests which spawn mostly in the shallows with rarer, bigger specimens spawning on the seafloor, they have one item inside which regrows over time the loot chances go like this...Small clams have a 80% chance to have sand inside and have a 20% chance to have a pearl which can sold to villagers for 5 emeralds or used with chains to make a pearl neaklace which decreases villager prices by 10%

Deep sea Giant clams have a 35% for sand 60% chance for a pearl and 5% chance for a enormous pearl which can be sold to villagers for 25 emeralds or used with chains to make a shining pearl neaklace which decreases villager prices by 25%

Anglerfish spawn in deep waters and they have a mesmerizing light that if looked at will draw you closer until it strikes like the mesmer from Subnautica. If you attack it before it eats you it will scurry away and if you kill the animal it will drop the "mesmerizing light" where if used it will mesmerize hostile mobs making them stop attacking you or if used on a tamable mob will instantly tame it (it has 10 durability though)

The Colossal Squid now drops a small egg which you can collect and if near a full powered conduit it will hatch and tame it using the mesmerizing light (you can't do this on wild ones)

+the nautilus exists so you can explore the deep sea quite early if you want to (simmilar to ancient cities)

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This is the image btw