Compass jellyfish
A common hydroid medusa , often called a ‘ many-ribbed jellyfish ’ or ‘ crystal jelly ’ the lion ’ s mane tentacle span might make it technically the largest , the chunkiest by far is the barrel jellyfish ( Rhizostoma pulmo ). I can attest to its solidity from the thud with which one hit the back of my head while I was preoccupied filming in a strong current !
A sixth species , the mauve stinger ( Pelagia noctiluca ), is a much less frequent sight but has a striking appearance , with an overall purplish hue and a globe-shaped umbrella . This is covered in prominent warts that contain powerful stinging cells . The sting can produce a very severe reaction .
I sneaked the word ‘ true ’ in earlier because the picture is confused by other jellyfish-like creatures we see at this time of year . Many of these are the free-swimming medusa stages of hydroids that also have a bottom-living polyp stage at a different time in their life cycle . Hydroid medusae are generally smaller and more delicate than ‘ true ’ jellyfish but some species can
be prominent . One that I have seen many times in the last few years is sometimes described as the ‘ many-ribbed jellyfish ’ or ‘ crystal jelly ’; its scientific name is Aequorea but the exact species is uncertain .
There are also comb jellies , which come in a variety of shapes and sizes . These belong to a different phylum ( Ctenophora ) from all the jellyfish , hydroids , sea anemones and corals ( Cnidaria ) but they look very much like small jellyfish . They are characterised by comb rows that run down the outside of the body and often have a beautiful iridescence . They propel the animal along and do make the small round ones slightly resemble a gooseberry . Comb jellies do not have stings but use sticky cells for capturing plankton prey . In turn , they can be eaten by moon jellyfish which , if eaten by a lion ’ s mane , gives us a jelly food chain ! �
Moon jellyfish
Small comb jelly known as a ‘ sea gooseberry ’
A well-armed lion ’ s mane with its impressive spread of tentacles
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