What kingdom has most of its species living entirely in water?

The kingdom that has most of its species living entirely in water is the Protista. The Protista kingdom includes a diverse group of eukaryotic microorganisms, many of which are aquatic. Examples of protists that live entirely in water include:

- Algae: Microscopic organisms that are able to photosynthesize, often found in marine and freshwater environments.

- Protozoa: Single-celled organisms that are heterotrophic, meaning they obtain their food by ingesting other organisms. Many protozoa are found in aquatic habitats.

- Water molds: Fungal-like organisms that live in water and feed on organic matter.

- Slime molds: Amoeba-like organisms that move and feed by gliding along surfaces, commonly found in moist environments.

- Diatoms: Unicellular algae that are encased in a silica cell wall, found in both marine and freshwater ecosystems.