The animal phylum most like the protists that gave rise to the animal kingdom is see concept 33.1 (page 688)

Porifera

The animal phylum porifera constitute the sponges that is most like the protists that gave rise to animal kingdom. One evidence is that they have been defined as multi-celled immobile animals or metazoans that have water intake and outlet openings, which is connected by chambers lined with choanocytes or cells with whip-like flagella. Another evidence that supports this includes the lack of true tissue in sponges.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.