It's got no brain, no bones, no heart, no eyes and only a basic nervous system, but despite its lack of substance the Marine Conservation Society (MCS) wants to know if you spot one.

It's got no brain, no bones, no heart, no eyes and only a basic nervous system, but despite its lack of substance the Marine Conservation Society (MCS) wants to know if you spot one.

MCS is asking British seaside visitors to report sightings of some of the most bizarre but fascinating creatures found in UK waters - jellyfish.

Large gatherings, or blooms, of jellyfish have already been reported in England, Scotland, Wales and Northern Ireland and as the UK's seas warm up during the summer, more jellyfish blooms are expected.

This year's jellyfish season started in earnest in March, when huge barrel jellyfish were reported off Ayrshire, Pembokeshire and Cornwall. The MCS Jellyfish Survey received reports of barrel jellyfish through April and May, when reports of the common moon jellyfish started coming in from around the UK.

In May MCS also received reports of a massive blue jellyfish bloom around the Cornish Peninsula, which continued through June. Some of these blue jellyfish were mistakenly identified as lion's mane jellyfish, which resulted in hysterical mis-reporting in the national press in June.

'Lion's mane jellyfish are being reported off the North West of the UK, like they are every year, so there is no need for panic,' said Peter Richardson, MCS Biodiversity Programme Manager. 'Lion's mane jellyfish and other species can give a painful sting, so as ever, we are encouraging holidaymakers to take part in the MCS jellyfish survey and report their jellyfish encounters, but the key message is look, don't touch!'

The aim of the MCS Jellyfish Survey is to understand more about where and when jellyfish occur around the UK. It's part of a wider MCS programme to discover more about leatherback turtles who migrate thousands of miles to UK waters to feed on their favourite jellyfish prey each summer. By mapping where and when the jellyfish are seen, MCS hopes to understand more about leatherback turtles while they visit in UK seas.

Over 5,000 jellyfish encounters have been reported since the MCS Survey was launched in 2003. The survey data is being fully analysed in collaboration with the University of Exeter and early results of the public sightings show interesting differences in the distribution of the larger jellyfish species around Britain (see table below).

In the last three years the survey has also detected an increasing presence in UK waters of hazardous jellyfish.

In 2007, 2008 and 2009 Portuguese Man of War were reported in large numbers in late summer strandings on beaches in the South West, and over the same period the Mauve Stinger bloomed in huge numbers off Ireland, Northern Ireland and the west coast of Scotland. It remains to be seen if these reports represent the start of a trend of these species occurring more regularly in UK waters.

Taking part in the jellyfish survey is easy! The full-colour MCS jellyfish photo-ID guide and recording forms can be downloaded from www.mcsuk.org , where jellyfish encounters can also be reported in detail online.