According to the ever reliable (!) wikipedia the Gorgon was a "vicious female monster with sharp fangs and hair of living, venomous snakes". Also, Gorgons are sometimes depicted as having 'wings of gold', 'brazen claws' and the 'tusks of boars'. According to the myths, seeing the face of a Gorgon turned the viewer to stone.
There are three Gorgons in total, with Medusa being the most famous. Of the three (which also includes Stheno and Euryale) Medusa was the only mortal - which handily explains why the mighty strong Perseus was able to chop off her head and kill her. Perseus cleverly used a mirror to ensure that he was never directly looking into Medusa's glare.
It's been suggested by some that Jane Asher could very well be playing a modern version of Medusa, or one of the other Gorgons, in the second SJA adventure - "Eye of the Gorgon". The storyline supposedly concerns an old person's home where an elderly family member of one of the team resides. Whether this turns out to be the case is any Gorgon's guess...
"Eye of the Gorgon" forms episodes three and four of the forthcoming Sarah Jane Adventures. Expect it to air sometime in early October - more detailed TX details closer to broadcast.
For anybody who wants to watch a classic piece of Gorgon action, the 1964 Peter Cushing starring Hammer Horror, "The Gorgon", airs Tuesday 28th August on BBC Two at 11:20pm.