Diario de f-sundw

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

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 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 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.

Modeeria rotunda

Still to see...

Leuckartiara sp. & Neoturris pileata

Umbrella 1-6cm high.
The above photos are of young medusa. I've noticed two distinct forms of these, the less typical one having less tentacles around the umbrella margin and a less pointed, more spherical apical process. Im unsure if these are the same species or not as I've seen the less typical form near adult size but not completely...
L. octona and L. nobilis (from one record) are the only Leuckartiara species recorded off Scotland. I havent looked further into identifying them after reading this paper and getting very confused on the possibilites of these medusa being Neoturris pileata. If anyone can help add to this I would greatly appreciate it!
https://www.inaturalist.org/observations/213240625
https://www.inaturalist.org/observations/213240626

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.

Melicertum octocostatum

Umbrella 1-2cm high.
https://www.inaturalist.org/observations/216360692

Proboscidactyla stellata

Still to see...

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.

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...

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.

Laodicea undulata

Umbrella ~2cm wide.
https://www.inaturalist.org/observations/216177070

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.

Halopsis ocellata

Still to see...
Not yet recorded off the West coast but has been off the North.

Eutima gracilis

Still to see...

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

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

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