What type of jellyfish is this?
If the jellyfish your friends saw actually look like this and if they were small (Wikipedia says they're usually less than 7 cm in length), they're likely Vellela vellela or sometimes called By-the-wind Sailors for the way the raised part catches the wind and is blown along the ocean's surface.

Wikipedia writes 


  ...all possess nematocysts, in some species the nematocysts and toxins
  therein are more powerful than other species. V. velella's nematocysts
  are relatively benign to humans, although each person may respond
  differently to contact with the nematocyst toxin. It is wise to avoid
  touching one's face or eyes after handling V. velella, and itching may
  develop on parts of the skin that have been exposed to V. velella
  nematocysts.


Some photos.

Source


Source