Bathic worlds are dwarf water worlds. They are only found in the temperate zone around stars. Any closer and the seas will boil off, any further out and they'll freeze (maybe becoming Stygian worlds. As well as having deep oceans, they often have an atmosphere of water vapour, which often shrouds the worlds in thick white clouds.
Carbon Dioxide atmospheres are possible, often leading to carbonated oceans.
The oceans are tens if not hundreds of kilometres in depth, and the low gravity can lead to huge perpetual wave systems across the upper surface of the world. They may have life in the depths.