Young eels are called glass eels.

yes when they get bigger they will become a different color

The types of eels are salt water eels, freshwater eels, the swamp eels, rubber eels and the electric eels. It is an elongated fish that lives in the shallow waters.

We do not know as eels do not leave good fossils. Also your English is a bit wrong your question should be worded "How many extinct eels were there". This is because if they are extinct they would have lived in the past not the present.

Adult eels are called eels, babies are elvers