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What are some examples of cnidarians? In which environments can these animals be found?

Jellyfish, hydra, corals and sea anemones are examples of cnidarians. Cnidarians are all of them aquatic and most live in the sea.

What are the two main morphological patterns of cnidarians? Concerning locomotion how do these forms differentiate from each other?

Morphologically, cnidarians classify as polyps or medusae. Polyps are cylindric and medusae are circular convex, like an umbrella. Both shapes have tentacles.

In general polyps are sessile but some species, like hydra, can move by alternating contact points on the substrate and performing somersaults. Medusae can move expelling water jets by contraction of the body.

Some cnidarians alternate polypoid and medusoid forms in their life cycle.

Concerning tissue complexity how different are cnidarians from poriferans?

Cnidarians have true tissue differentiation, they present distinct organized tissues in the body. Poriferans present only some dispersed specialized cells with no tissue differentiation.