Both are from Domain Eukarya, are unicellular and are water organisims
Yes. Coelenterates are the same as Cnidaria.
Phyla is the plural of phylum. One phylum, many phyla.
Look for the traits of chordates. It is said that both sharks and humans are vertebrates or closely related invertebrates.
Phyllum is not used itself ,but members of this Phyllum are much important in producing red tides and bloom in sea as in red sea . These blooms are toxic to fish and other organisms+