Members of phylum porifera are

The correct option is "Mostly marine animals but few are fresh water entities".

Phylum Porifera, commonly known as sponges, consists of primitive, multicellular, pore-bearing animals. When analyzing their habitat, we observe the following characteristics:
1. Marine Habitat: The vast majority of sponge species (around 99%) inhabit marine environments, ranging from shallow coastal waters to the deep ocean floor. Examples include sycon, sponges of the genus Spongilla (excluding freshwater ones), and Venus' flower basket.
2. Freshwater Habitat: Only a very small group of sponges have adapted to live in freshwater environments (lakes, streams, and ponds). The most notable example is the family Spongillidae, which includes the genus Spongilla (freshwater sponges).

Therefore, because they are predominantly found in the seas and oceans with only a few exceptions in freshwater, they are correctly described as mostly marine animals but a few are freshwater entities.