Sea Monsters (5E)

From publisher blurb:

Beasts of the Briny Blue

Sea Monsters is an 80-page softcover DnD 5E bestiary featuring over 60 maritime monsters and nautical nemeses, from low-level minions of the deep like mutant selachim sahuagin and to reef hags, living islands to coral golems, savage predators like the devilfish and slaughtermaw lamprey, and legendary foes like the scylla, charybdis, and even the Midgard Serpent, alongside a marvelous array of monstrous sea life more familiar to our world like giant squid, megalodons, deep tiger anemones, shipwrecker crabs, and ravenous urchin swarms! Plus, you get expanded 5th Edition rules for aquatic adventuring!