My quick brainstorming (and seed for each):
Sea bottom (Nutrients from stuff raining down from above)
* Trilobyte - derivatives adapted for deep sea, big armored tanks
* Sea trees: Probably derived from coral, but able to root in the deep sea (for nutrients) and expand up near surface (for energy). Possibly exploit temperature differentials for transport & energy, and maybe have expendable tops (grow back fast) to weather storms.
* Varient amoebas that wander the sea bottom
* There are a couple of aquatic carnivorous plant types -- one of which entangles worms, and another that creates a vaccum in a pouch so that when the hatch opens it can suck in passing creatures
* STarfish are carnivorous. And can regenerate. Make them move fast enough, make them bigger, and that's pretty scarey
Surface (Nutrients from other animals or anchored at upwellings, energy from sun)
* Colony: Rift off Man-o-war, but a colony of animals and plants that is able to defend itself (stingers), float on the water, take advantage of best of air and water living. Storms would shred them, but each part would then regrow into a new colony
* Polyps of other species: It could be fun to have a poisonous/dangerous difference between the larval and adult states of animals.
* Philip Jose Farmer invented Wind Whale that stayed up through bouyant lighter-than-air sacs. You could do something like that to populate the sky without requiring land
* Free-floating sponges that clog intakes, or are big enough to be interesting
* Branched coral that has enough symbiotic species that it is protected against predators
* Giant rotifors that are big enough to create whirlpools when they are feeding, and can suck man-sized (or bigger) into their maws (Charybdis)
I'm sure you've run through variations of the interesting fish as well (sea horses, pufferfish, cows, skates, rays. Sea turtles?
Steve
Bathalians, the newest UberVillians!