Littoral Springtails of the UK

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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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Posted on 05 de abril de 2024, 09:40 AM by josscarr