The sun shines right through the crystal clear jelly of this Compass Jellyfish, Chrysaora hyoscella (Linnaeus), washed ashore on a Gower beach. The clear jelly is called mesoglea – it is thick, gelatinous, and fibrous. The radiating red-brown v-shaped lines, decorating the ex-umbrella or aboral surface of the shallow saucer-shaped dome, give this small jellyfish its common name. The specimens in these pictures were stranded at Port Eynon and Rhossili Bay at various times. These individuals measure no more than 150 mm across but this species can grow to twice that size.
Compass Jellyfish are Coelenterates belonging to the Class Scyphozoa. The adult free-swimming animal is known as a medusoid form. They have the jelly filled bell or dome on the circular edge of which are scalloped lappets. You can see these lappets in the photographs of the upside-down jellyfish below where they look like red/brown coloured semi-circles or triangles around the curled-in edge of the dome. The very small tentacles, also around the edge with the lappets, cannot be distinguished in these pictures.
The animal’s mouth is on a stalk called the manubrium that is drawn out into four oral arms that hang down from the centre of the sub-umbrella, oral, or under surface of the dome while it is swimming. These oral arms are visible as four long red-brown appendages radiating irregularly from the centre of the underside. amongst the sand, in the stranded specimen below.
For some more details of jellyfish and their biology, click here for information on the much larger Dustbin-lid or Barrel-mouthed Jellyfish – also tending to get washed up on Gower seashores.
Revision of a post first published 29 October 2009
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Jessica's Nature Blog 
Have NEVER seen anything lke this compass jellyfish! Especially love the first photo.
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I understand these are supposed to be fairly common but I was totally amazed the first time I saw one a couple of years ago.
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Beautiful creatures, and your description is wonderful.
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Thank you, Ian. Your comments are appreciated.
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We spotted one swimming between us in shallow water while paddling on a beach Mewslade Bay, Gower. It looked a little more pinky coloured than these in the photos, but had the same markings. Beautiful to watch it swimming.
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Hello, Amanda.
The Compass jellyfish certainly is a most beautiful creature. I have never seen one actually swimming. Maybe I’ll be lucky enough to see one in a few weeks time when I shall be staying very close to Mewslade Bay. The colour of the markings is variable and affected by the quality of light in which you are viewing them. Photographs are also not so reliable for their representation of colour either – sharpening the image can darken the colours.
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Hi Jessica, We saw it in the afternoon when the tide was nearly full in. I was about thigh deep and the waves were keeping it close to the shore. Quite magical watching it swimming. Fun trying to avoid it when the waves came! Good luck jellyfish hunting.
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Thank you, Amanda. I’m wondering if the jellyfish will be an inspiration for one of your artistic creations. Your paintings are beautiful.
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