How many kinds of jellyfish are there??

In the last 20 years, using scuba, manned and unmanned submersibles, scientists have discovered more than 50 new species of jellies. Madin, an expert on jellies, has discovered more than half a dozen species.

In Florida USA, experts of Oceangraphy found more than 67 species of jellyfish & 50 of them are commonly seen in most oceans.
The most fierce one named Portuguese-man-of -war which has very long & beautiful threadlike parts that hang beneath it, but it is terribly poisoning.