Bearing in mind that everything is magnified under water, these could be sea centipedes - if so keep away as they can give you a nasty sting which is much like an acid burn. I was stung by one whilst swimming in Selimiye bay near Bozburum a few years ago and had really hard sore hard blisters across the back of my hand for ages. I also saw a local Turkish lad who had been stung on the stomach. One night we watched the locals hauling them up from the harbour and they then "pis*ed on them and they split into two much like worms - yuk -horrible things!!!
