Sload. Dreugh (they look different when they're in their aquatic phase:)
Fish of various sorts, including the aforementioned Slaughterfish. Different types of coral. Sheogorath mentions narwhals, so probably different sorts of whales. Kollop and other types of clams, oysters and so on. Giant sea-serpents per the Aldmeri Dominion questline. Shipwrecks.
And the water itself is made from the memories of dead mortals, as per a side quest in Bangkorai.