Hydromedusa off the West coast of Scotland
Hydromedusa are the adult reproductive stages of Hydrozoa, often confused with true jellyfish (Scyphozoa), and seem very under-recorded in citizen science (at least in the UK) despite being very abundant during the Spring and Summer and great fun to observe.
Most of my observations of hydromedusa have been from seeing and capturing individual medusa whilst snorkelling using an empty squeezy honey or shampoo bottle, which seems to be the easiest way to catch them without damaging them! (If you want to do this yourself please put them back once you have taken photos, some, like Hybocodon prolifer, seem to be only able to live a day in captivity!)
I intend to update this post as I record more. I have also included (in their own sections) siphonophores (they are hydrozoa but not medusa) and other interesting plankton you may come across that I have also!
Hydromedusa
This guide for jelly monitoring at fisheries on the West coast of Scotland has been a huge help for me and is worth checking if you need any further reference.
The following are ordered loosely by visual similarity:
Hybocodon prolifer
Umbrella 2-4mm high.
I see medusa of H. prolifer more often than anything else, floating around in the sufrace waters. The genus is distinguished by having 1 tentacle bulb and 4 radial canals, one of which is longer than the rest, giving a lopsided appearance. H. prolifer is distinguished from the other species of the genus (not recorded off Scotland) by the fact that it buds medusa from its tentacle bulb.
Visually similar to Corymorpha nutans and Euphysa aurata but can be differentiated by its lopsided umbrella.
https://www.inaturalist.org/observations/164423728
https://www.inaturalist.org/observations/210471569
https://www.inaturalist.org/observations/213427675
https://www.inaturalist.org/observations/228638524
https://www.inaturalist.org/observations/236157704
Euphysa aurata
Umbrella ~4mm high.
Seen much less frequently than Hybocodon prolifer and can look very similar from afar. The species name E. aurata name may hold some cryptic species also (see here and note their paper is still under work as of writing). Note: this species can vary in appearance significantly from the photo here.
Visually similar to Corymorpha nutans and Hybocodon prolifer but can be differentiated by its lack of an apical process and non-lopsided umbrella respectively.
https://www.inaturalist.org/observations/213427676
Corymorpha nutans
Still to see...
Visually similar to Euphysa aurata and Hybocodon prolifer but can be differentiated by its notable apical process and non-lopsided umbrella respectively.
Sarsia sp.
Umbrella 5-8mm high in S. tubulosa (as in the above photos).
Sarsia species can be quite hard to identify, I would recommend using this paper to identify them (under the knowledge that S. tubulosa is suspected as a species complex by the author and has many forms). S. tubulosa, S. striata, S. densa, S. occulata and S. piriforma (and maybe Sarsia lovenii) are the species with free-swimming medusa previously recorded off Scotland.
Visually similar to Coryne exima, Codonium proliferum, Stauridiosarsia gemmifera and Slabberia halterata but can be differentiated by its manubrium that (when relaxed) hangs below the end of the umbrella and is surrounded by one entire gonad, not multiple segments of gonads as in the latter two species.
https://www.inaturalist.org/observations/208551702
https://www.inaturalist.org/observations/213005407
Coryne exima
Still to see...
Codonium proliferum
Still to see...
Stauridiosarsia gemmifera
Still to see...
Slabberia halterata
Still to see...
Bougainvillia principis
Umbrella ~7mm wide by ~5mm high (can be as small as 1mm high).
Visually similar to B. britannica and B. muscus but, when its a mature medusa, can be differentiated by its many more tentacles per tentacle bulb and denser branching of its 4 manubrium lips. See this paper for more details.
https://www.inaturalist.org/observations/214803648
Bougainvillia britannica
Still to see...
See this paper for more details.
Bougainvillia muscus
Still to see...
See this paper for more details.
Bougainvillia pyramidata
Still to see...
Not yet recorded off the West coast but has been off the North.
Modeeria rotunda
Still to see...
Amphinema dinema
Still to see...
Amphinema rugosum
Umbrella 4mm high.
The medusa shown above appears to be a female with eggs, the male gonad texture will be different.
https://www.inaturalist.org/observations/227325467
Leuckartiara octona
Umbrella 0.5-1.5cm high.
Visually similar to L. nobilis but can be diffrentiated by the presence of abaxial spurs on their tentacle bulbs. Also visually similar to Neoturris pileata but can be differentiated by the presence of occeli on the tentacle bulbs and lack of a flatter, pitted area between gonad folds.
Please note that medusa can vary significantly in appearance, looking at the gonads is the most consistent part in the family.
See this paper for more details.
https://www.inaturalist.org/observations/231262258
https://www.inaturalist.org/observations/232059450
Leuckartiara nobilis
Umbrella 0.5-1.5cm high.
Visually similar to L. octona but can be diffrentiated by the lack of abaxial spurs on their tentacle bulbs. Also visually similar to Neoturris pileata but can be differentiated by the presence of occeli on the tentacle bulbs and lack of a flatter, pitted area between gonad folds.
Please note that medusa can vary significantly in appearance, looking at the gonads is the most consistent part in the family.
See this paper for more details.
https://www.inaturalist.org/observations/213240626
Neoturris pileata
Umbrella 1-6cm high.
Visually similar to Leuckartiara sp. but can be differentiated by the lack of occeli on the tentacle bulbs and the presence of a flatter, pitted area between gonad folds.
Please note that medusa can vary significantly in appearance, looking at the gonads is the most consistent part in the family.
See this paper for more details.
https://www.inaturalist.org/observations/213240625
https://www.inaturalist.org/observations/231262261
Turritopsis polycirrha
Still to see...
Turritopsis nutricula
Still to see...
Rathkea octopunctata
Umbrella 2-3mm high.
Buds more medusa from the stomach wall, typically has multiple tentacles per tentacle bulb, manubrium has 4 lips that each split in two and end in nematocyst clusters, eight in total.
Visually similar to Podocoryna borealis and Lizzia blondina but can be differentiated by its 4 mouth lips splitting into 2 knobbed arms, not 1.
https://www.inaturalist.org/observations/213005408
https://www.inaturalist.org/observations/214803653
Podocoryna borealis
Still to see...
Visually similar to Rathkea octopunctata and Lizzia blondina but can be differentiated by its 4 mouth lips not splitting, and by its lips not originating from above the mouth margin respectively.
Lizzia blondina
Still to see...
Visually similar to Rathkea octopunctata and Podocoryna borealis but can be differentiated by its mouth lips not splitting, and by its lips originating from above the mouth margin respectively.
Aglantha digitale
Still to see...
More frequent on the East and North coast. On the West: not expected inland, previously recorded in deeper waters.
Melicertum octocostatum
Umbrella 1-2cm high.
https://www.inaturalist.org/observations/216360692
Proboscidactyla stellata
Umbrella ~4mm high and wide.
https://www.inaturalist.org/observations/246292688
Ptychogena crocea
A few records off the West coast, which are beyond the Outer Hebrides and more Northern.
Ptychogena lactea
Still to see...
Only one record off the West coast, which is beyond the Outer Hebrides.
Earleria panicula
Still to see...
Only one record off the West coast, which is beyond the Outer Hebrides.
Obelia sp.
Umbrella ~1cm wide.
Quite characteristic, eyelash-like medusa with a wine glass shaped manubrium.
Visually similar to Phiaella quadrata but can be differentiated by the manubrium lip shape.
https://www.inaturalist.org/observations/213005410
Phiaella quadrata
Still to see...
Visually similar to Obelia sp. but can be differentiated by the manubrium lip shape and how its tentacles are much fewer and are borne from much larger tentacle bulbs.
Ptychogena crocea
Still to see...
Ptychogena lactea
Still to see...
Clytia sp.
Umbrella ~1.5cm wide.
Quite common where I am, the gonads on the 4 radial canals often appear more brightly blue/green due to biofluorescence. The most commonly recorded species is C. hemisphaerica but molecular analysis is needed to differentiate medusa stages in this genus.
https://www.inaturalist.org/observations/209053415
Mitrocomella polydiademata
Still to see...
Lovenella clausa
Still to see...
Laodicea undulata
Umbrella ~2cm wide.
https://www.inaturalist.org/observations/216177070
Cosmetira pilosella
Umbrella 2-4cm wide.
Visually similar to Earleria panicula, Laodicea undulata and Staurostoma mertensii but can be differentiated most confidently by its marginal cirri (small tentacles) receeding up the umbrella slightly.
https://www.inaturalist.org/observations/216177075
Earleria panicula
Still to see...
Only one record off the West coast, which is beyond the Outer Hebrides.
Staurostoma mertensii
Still to see...
Visually similar to Cosmetira pilosella, Earleria panicula and Laodicea undulata but can be differentiated by its lack of a central manubrium.
Eutima gracilis
Still to see...
Rhopalonema velatum
Still to see...
Not expected inland, previously recorded in deeper waters.
Halopsis ocellata
Still to see...
Not yet recorded off the West coast but has been off the North.
Solmaris corona
Still to see...
Some other Narcomedusae have been recorded in the UK (though only to Genus level), Solmundella, Aegina and Aeginura.
Aequorea forskalea
Sometimes appears in large blooms.
Visually similar to A. vitrina, the only other species recorded off Scotland, but can be differentiated by having between <1 and 2 tentacles per radial canal) unlike A. vitrina which has at 2+ tentacles per canal. (Here is my reference.)
Normally molecular analysis is needed to differentiate species of Aequorea, but off the coast of Scotland, the two species found here happen to be morphologically different.
https://www.inaturalist.org/observations/178974121
Aequorea vitrina
Still to see...
See under 'Aequorea forskalea' for differentiation.
Siphonophora
The majority of siphonophores will hold themselves in the water as a long string of polyps that it hang tentacles down to catch prey.
The following are just the siphonophores I've seen off Scotland, to Identify siphonophores I would reccomend using this book.
Some species, like Muggiaea sp. could possibly be confused with hydromedusa like Corymorpha nutans, Euphysa aurata and Hybocodon prolifer.
Nanomia cara
https://www.inaturalist.org/observations/216360690
https://www.inaturalist.org/observations/228638525
Other mesoplankton
Aurelia aurita
Umbrella ~2cm wide.
This photo is of a very young moon jelly.
https://www.inaturalist.org/observations/213005406
Cyanea capillata
Umbrella ~2cm wide.
This photo is of a very young lion's mane jelly.
https://www.inaturalist.org/observations/213240618
Pleurobrachia pileus
Body ~1cm high.
https://www.inaturalist.org/observations/213427666
Bolinopsis infundibulum
Body 2-4cm high.
https://www.inaturalist.org/observations/215788544
https://www.inaturalist.org/observations/232059448
Beroe cucumis
Bear in mind that another Beroe sp. has been recorded off the East coast (B. gracilis) but this seems to be the only one on the West.
https://www.inaturalist.org/observations/236543951
Tomopteris helgolandica
https://www.inaturalist.org/observations/216072535
Larvaceans
Above are Oikopleura dioica.
Larvaceans are often seen in early Summer but very under recorded, they will appear as a small mucous ball with a speck in the centre in the water. To identify I would reccomend using this book.
https://www.inaturalist.org/observations/210471575
Anemone larvae
https://www.inaturalist.org/observations/216072534
