What type of jellyfish is this
Eventually, I've stumbled upon an article which calls it a cigar jellyfish.

Further research even shows a very empty entry on Wiki about it, which consists of the single line entry:


  The cigar jellyfish (Olindias phosphorica) is a species of jellyfish from the Central and East Atlantic, and the Mediterranean Sea, including off Malta.[2]


Also an interesting article about it being 'rare' in Malta (despite the above information)