Diario de josscarr

I know of four* UK species in the family Isotomidae which fit a similar description: they are roughly yellow-ish as the base colour and then have at least one dark longitudinal stripe running the whole length of the abdomen. There are four species which match this description and are listed on the NBN Atlas. They are:

1. Isotoma riparia
2. Isotomurus palustris
3. Isotomurus plumosus
4. Isotomurus unifasciatus*

*Isotomurus unifasciatus clearly 'fits the bill' in terms of generally resembling the other three species but is of unclear status in the UK (according to here). As such it is probably best to not consider this species an option for ID, although keeping it in mind is worthwhile!

Ignoring Isotomurus unifasciatus, we can make some headway towards determining which species an observation shows by looking at (1) the setae (tiny hairs) and (2) the pigmentation pattern.

Step 1: Is the specimen Isotoma riparia?

As outlined here, Isotoma species as a whole can easily be distinguished from Isotomurus species by looking at the setae on the abdomen. Specifically, Isotoma species have macrosetae (large hairs) on all body segments, whereas on Isotomurus species there are macrosetae BUT they are confined to the last two or three posterior (back) segments, and are absent from the front of the abdomen. To visualise this difference compare some of the photos of Isotomurus here with those of Isotoma here. Following this general rule, it should be clear when a given striped and yellow-ish UK Isotomid is Isotoma riparia. Simply look at where the long hairs are! Generally, we might expect Isotoma riparia to be quite rare because there are only a few records of it in the UK so far (source). Of those, all have been from very wet habitats, including two places along the river Thames and a salt marsh in Dorset (source). If any more records of this species turn up, we might expect them to be from similar places. If there are from very different places (i.e. quite dry habitats), microscopic examination would likely be necessary to make extra sure the ID is correct (N.B. microscopic examination might be warranted anyway, given the species' relative rarity!).

Step 2: Isotomurus palustris vs. Isotomurus plumosus

Having eliminated Isotoma riparia from consideration, and ignoring Isotomurus unifasciatus, the choice is then between Isotomurus palustris and Isotomurus plumosus. If one compares photos of the two species (e.g. here), a slight difference in pigmentation pattern should be clear. Namely, whilst both species have three longitudinal stripes, on Isotomurus palustris all three are clearly visible from the top-down, whereas with Isotomurus plumosus the lateral stripes are only just visible from the top-down and much better seen from a side angle. Isotomurus palustris also seems to have some additional patches of dark pigment as well as the three stripes, whereas Isotomurus plumosus tends not to. Finally, Isotomurus plumosus is described here as being restricted to wet habitats, so habitat description can contribute to an ID too. All that being said, though, being scientifically rigorous, I doubt these differences in pigmentation are truly diagnostic enough to ever be 100% certain of the species' true identity. Therefore, I recommend for these two species putting the iNaturalist ID at genus Isotomurus, then adding a note with 'c.f." and then the species name of choice, to indicate a tentative ID. Having done that, it is then probably the best course of action (provided there are at least two IDs at genus) to have identifiers press 'good as can be' in the data quality assessment (DQA) section of the observation. This will make the observation research grade at genus. To ensure the tentative ID doesn't get lost if the observation data is transformed, it would also be best to add the suggested possible ID as an annotation using the "Possible ID" field.

Hope that helps! :)

One of the few UK Onychiuroidea springtails that can be distinguished from photographs alone is Kalaphorura burmeisteri. To quote Matthew Shepherd (a UK Soil Ecologist): "this is one species that can be identified by shape alone. It's the only white, blind, springless podger that his this tapering shape, fattest around the middle. Often compared to the Michelin man!"

Original source (including photos) is this facebook post.

Contrary to Dallimore and Shaw's (2013) 'Illustrated key to the families of British Springtails (Collembola)', it is not a universal rule that distinguishing UK springtails from the families Onychiuridae and Tullbergiidae (together superfamily Onychiuroidea) from UK springtails in the family Hypogastruridae (having eliminated from consideration Neanuridae, Poduridae and Odontellidae), is a simple matter of considering all white (unpigmented) springtails as Onychiuroidea and all non-white (pigmented) springtails as Hypogastruridae.

Rather, there are a few outliers to this general rule – the relatively few but still considerable species of unpigmented Hypogastruridae. Some of these resemble Onychiuroidea, at least to an untrained eye. Of those for which there are photos listed on the global Collembola database, there are at least 5 species of unpigmented Hypogastruridae:

• Ceratophysella succinea
• Ceratophysella armata
• Schaefferia emucronata
• Xenylla grisea (juveniles)
• Mesogastrura libyca

To identifiers with experience, most of these species are quite distinctly different from Onychiuroidea, but Mesogastrura libyca in particular looks very similar to some members of the superfamily. It should also be explicated that many Hypogastruridae species lack photographs on the database and so could also easily also be unpigmented and similar in appearance to some Onychiuroidea.

I therefore urge that caution should be taken when distinguishing Hypogastruridae from Onychiuroidea on the exclusive basis of pigmentation. In cases where appropriate detail is not obvious, observations should be left at order.

As far as I am currently aware, the two Poduromorpha springtail families Neanuridae and Hypogastruridae cannot easily be distinguished from one another based on field photography alone. Rather, assuming the species is not otherwise obvious, details only visible through microscopic analysis may well be needed.

It is notable that this assertion differs with that made by Dallimore and Shaw's (2013) 'Illustrated key to the families of British Springtails (Collembola). According to that key, the choice between families can be made based on the 'distinctiveness' of the head from the thorax. In Neanuridae, it is argued, the head is indistinct, whereas in the other UK Poduromorpha families (Odontellidae, Poduridae, Onychiuridae, Tullbergiidae and Hypogastruridae), the head is distinct.

I am inclined to disagree with Dallimore and Shaw's key here because the 'distinctiveness' of the head from the thorax is not a binary property. Rather, 'distinctiveness' varies considerably along a gradient from 'clearly distinct' to 'clearly indistinct'. It is not a clear-cut matter. Furthermore, not only does distinctiveness appear to differ between species within the two families, it is also likely that distinctiveness can vary between individuals within a species (i.e. intra-specific morphological variation), and even over time for a single individual (based on environmental conditions, whether the springtail is feeding, resting, etc.).

See original discussion on these two observations:

• https://www.inaturalist.org/observations/198764269
• https://www.inaturalist.org/observations/191698747

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According to Steve Hopkin (a UK Collembola expert) on his website, there are 23 species of 'littoral' (meaning intertidal/seashore) springtails found in the UK. The French website DORIS (which collates records of marine animals and plants) mentions one additional species (Hypogastrura viatica) as also being found on North Atlantic seashores (see here). Combining these gives a total checklist for UK littoral springtails numbered at 24 species. It should be noted that this checklist for Icelandic springtails describes several other species (most of which are also found in the UK) as littoral, however uses a broader definition of littoral as including coastal habitats in general (e.g. sand dune systems). Here my focus is specifically on springtails found on beaches and rocky coasts in the intertidal zone, hence these additional species are ignored. The 24 springtails which are considered as littoral here are split across two orders (Poduromorpha and Entomobryomorpha) and five families (Hypogastruridae, Neanuridae and Onychiuridae within Poduromorpha; Entomobryidae and Isotomidae within Entomobryomorpha). The full checklist is as follows. The species names which are in bold are those for which there are photos published online. Note that this is not the case for all species.
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Checklist:

Hypogastruridae

• Hypogastrura viatica
• Xenylla humicola
• Xenylla maritima

Neanuridae

• Friesea acuminata
• Anurida maritima
• Anurida thalassophila
• Anuridella immsiana
• Anuridella marina
• Anuridella submarina
• Gastranurida (/Anurida) denisi

Onychiuridae

• Protaphorura macfadyeni
• Thalassaphorura debilis
• Thalassaphorura halophila

Entomobryomorpha

Entomobryidae

• Mesentotoma dollfusi
• Pseudosinella halophila
• Pseudosinella petterseni

Isotomidae

• Archisotoma besselsi
• Archisotoma megalops
• Archisotoma pulchella
• Archisotoma theae
• Folsomia sexoculata
• Axelsonia littoralis
• Halisotoma maritima
• Halisotoma poseidonis

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Identifying to Order:

According to Dallimore and Shaw's (2013) 'Illustrated key to the families of British Springtails (Collembola)', Poduromorpha and Entomobryomorpha can be easily distinguished from one another by examining the first thoracic segment. Both Poduromorpha and Entomobryomorpha have three thoracic segments. In Entomobryomorpha, however, the first thoracic segment of the three is greatly reduced dorsally, such that it almost appears as if the springtail has a restricted 'neck'. Poduromorpha, in contrast, have a clearly visible first thoracic segment. For an obvious example of the difference, compare this observation with this observation.
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Poduromorpha:

Within Poduromorpha, the Order which contains 13/24 of the UK littoral species, there is, technically speaking, no hard-and-fast way to distinguish Hypogastruridae, Neanuridae and Onychiuridae (at the family level) without microscopic examination of specimens (for more info see this and this other two journal posts of mine). This being said, one can get a fair way based on colour, as follows:

N.B. for species without photos published online I have assumed the likely colour based on best evidence (e.g. colour of other UK species in the genus).

DARK GREY/DARK BLUE/PURPLE (5 species):

• Hypogastrura viatica
• Xenylla humicola
• Xenylla maritima
• Anurida maritima
• Gastranurida (or Anurida) denisi (no photos, however most likely this colour as per here and here)

YELLOW (4 species)

• Friesea acuminata
• Anuridella immsiana (likely yellow, given Anuridella marina is definitely yellow, as is this unidentified UK Anuridella species)
• Anuridella marina
• Anuridella submarina (see above notes for Anuridella immsiana)

WHITE (4 species)

• Anurida thalassophila (no photos of live specimens, however these microscopy photos show white colour, plus Steve Hopkin's website says the species appears similar in general appearance to Anurida granaria, which is white)
• Protaphorura armata
• Thalassaphorura debilis
• Thalassaphorura halophila (no photos, however all other UK members of Thalassaphorura are white, so the chances are very high this species is too)

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Entomobryomorpha:

Within Entomobryomorpha, which contains 11 littoral species, the first division needs to be made between Entomobryidae and Isotomidae. Fortunately, this is straightforward. Following Dallimore and Shaw (2013), Entomobryidae are easily identified to family if it is clear that the 4th abdominal segment is notably longer than the other abdominal segments. In contrast, Isotomidae are defined by all the abdominal segments being of similar length.

Having decided whether a given littoral springtail is an Entomobryid or Isotomid, it should be possible in most cases to go further to genus and sometimes species based on the colour and body form.

ENTOMOBRYIDAE (3 species):

• Mesentotoma dollfusi is very distinctive, resembling no other littoral springtail. It looks superficially similar to Entomobrya species.
• The two Pseudosinella species (Pseuodsinella halophila and Pseudosinella petterseni) are an almost translucent white colour, and have a body form loosely resembling frequently encountered Lepidocyrtus springtails. Distinction between species in the genus requires microscopy.

ISOTOMIDAE (8 species):

• The four Archisotoma species are either blue/black/grey-ish (Archisotoma besselsi, Archisotoma megalops and Archisotoma pulchella) or greyish-brown (Archisotoma theae). There aren't many photos online so this is a fairly tricky genus to try and identify without microscopy (though see here).
• Folsomia sexoculata is translucent-white with a darker longitudinal dorsal stripe
• Axelsonia littoralis is a shiny greyish-blue colour and is distinctively 'chunky' for an Isotomid springtail
• The two Halisotoma species (Halisotoma maritima and Halisotoma poseidonis) are greyish-blue and shaped more like a standard Isotomid. The two species cannot be distinguished without microscopy (as per here).

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Congregating behaviour:

A common behaviour often observed in littoral springtails (or at least some of them) is 'congregating' on the water surface of rockpools (e.g. see here). So far I have only seen this done by the dark-blue/grey/purple poduromorphs, but it may also be a behaviour of others. That being said, it is crucial to note that congregration is not a unique feature of any single given species. The behaviour is well-known in Anurida maritima (e.g. here) and has also been photographed in Xenylla humicola (see here). I would not be at all surprised if the other Anurida/Gastranurida/Xenylla species also congregated in this way.
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