True Jellyfish

Jellyfish are sea-going creatures, but are included here, as every year hundreds are washed up on the shore. The species found depends on the sea currents at the time. Jellyfish have to be seen soon after stranding, because as they are 99% water, they dry out fast and leave little trace. Forget jellyfish as a food source, as due to them being primarily water, they have no nutritional value.

As for the rest of the coelenterates they are only a simple organism, but depending on the species, can reach a large size. The majority of jellyfish are free swimming and possess a saucer or bell shaped body. The term free swimming is used loosely, as they can swim slowly and vary their depth, but are not strong swimmers. They are ineffectual against currents and are at their mercy, this is why they are commonly stranded on the shore and can be so in large numbers.

Jellyfish feed either by stunning or paralysing their prey with stinging structures called nematocysts, while other species trap and feed on plankton. As with the hydroids the life cycle varies with the species but generally there is a sessile polyp stage, but the dominant stage is as a medusa (jellyfish like stage).

There are a variety of species stranded on the Cornish shore, this being dictated by the currents, wind direction and season.

The two most recent specimens I have found are the moon jellyfish Aurelia aurita and the barrel jellyfish Rhizostoma pulma.

Barrel Jellyfish Rhizostoma pulma

Caution

Do not touch stranded jellyfish, as some species can sting, which can have serious implications.