Crystal Jelly, (Photograph  by Penny Martin, Orkney)

Crystal Jelly, Aequorea species
Photograph © by Penny Martin (Orkney)
12 July 2011, Birsay, Orkney Islands

Aequorea is a bioluminescent hydrozoan jellyfish, or hydromedusa.
True jellyfish are in the class Scyphozoa.

Aequorea are widely found around the British Isles with records washed up on the shore from Cornwall and Suffolk as well as the Orkneys. However, the records are not complete at the moment because the genus is often not recognised and any reports are welcome. Aequorea species need experts to distinguish between them. Aequorea forskalea has been positively identified and recorded from around the British Isles. The two reports of Aequorea I have received have both been in July 2011.


19 September 2009


There was a large stranding of jellyfsh-like Aequorea forskalea on Treyarnon Beach, North Cornwall coast.

Cornish Report and Photographs by Dave Fenwick (Aphtomarine)


BMLSS Jellyfish & related Medusa
BMLSS Cnidaria

Jellyfish Blooms

Last Friday I have made a night dive in the Grevelingen, the Netherlands,
surrounded by many Aequorea specimens. I've done some interesting
- Specimens drifting in less then 1 meter deep water, moreover had all
their tentacles retracted. Touching these medusa's they lighten up brightly.
In shallow water (<+/-1m) I saw over a hundred specimens.
- Stirring the water one could see many spots of light.... =
micro-organisms that emit light.
- Specimens drifting in deeper water, moreover had all their tentacles
elongated. Touching these medusa's (after turning off my own "diving
light"), none of them emitted any light. I've encountered about 20 of these
specimens during my dive Friday.
- I have encountered a few specimens (<10) with only a few of their
tentacles elongated. These specimens only sometimes emitted some light.
- Retracted tentacles are curled. (see photograph on my web-site)
- I have made various photographs from Aequorea with and without there
tentacles elongated. Today or tomorrow I will put these on my web-site:

- The Dutch Aequorea specimens emit light because they have
caught/eaten micro-organisms ("zeevonk"=Dutch name) that lighten up when
- The observation that medusae with retracted tentacles brightly emit
light and those with elongated tentacles do emit light at all, supports the
hypothesis that the medusae retract their tentacles when they have a full
- The Dutch Aequorea specimens, moreover elongate all their tentacles
in order to catch their food. When they have caught enough food they retract
their tentacles.
- No support was found for the hypothesis that the Dutch Aequorea
specimens have a limited number of specialised elongated tentacles.
- When a tentacle is retracted, it is curled, shortening this tentacle
even more.

kind regards,
Arjan Gittenberger

-----Original Message-----
From: Dhugal J. Lindsay []
Sent: Monday, July 24, 2000 3:36 AM
Subject: Re: tentacle elongation in hydromedusae 2

I know it's not a hydromedusa but just thought that while we were on the
subject of elongated tentacles...

Most people probably know by now the observation that the coronate
scyphomedusan Atolla is pretty much always seen in vivo with one elongated
hypertrophied tentacle and only one. We recently observed it to catch
Nanomia bijuga using this tentacle. Any interested people should refer to

Hunt, J.C., and D.J. Lindsay, 1998. Observations on the behavior of Atolla
(Scyphozoa: Coronatae) and Nanomia (Hydrozoa: Physonectae): use of the
hypertrophied tentacle in prey capture. Plank. Biol. & Ecol., 45(2):

or drop me a line for a reprint.

Subsequent SEM has identified the presence of nematocysts on the distal end
of this tentacle although we'll have to catch another before we can better
characterize the morphology and distriution.

Can't say I've ever seen Aequorea in the mesopelagic with some but not other
tentacles elongated. I do have at least one new species of Aequorea from the
Indian Ocean south of Mauritius if anyone is interested in giving the genus
an overhaul;-)

Ciao for now,


Dr. Dhugal J. Lindsay
Marine Ecosystems Research Department
Japan Marine Science and Technology Center (JAMSTEC)
2-15 Natsushima-cho,
  Japan Marine Science and Technology Center (JAMSTEC)
2-15 Natsushima-cho,