Antrobathynella stammeri / Bathynella natans
For accurate identification of specimens see Gledhill, T., Sutcliffe, D.W. & Williams, W.D., 1993 ‘British freshwater Crustacea Malacostraca: a key with ecological notes’ Freshwater Biological Association, Scientific Publication No. 52. A description of the Irish species Nipharguswexfordensis is provided in Karaman, Gledhill & Holmes (1994). For identification of Microniphargus leruthi see Schminke (2007) and Knight & Gledhill (2010).
The table below and the attached key provide a rough guide to the identification of specimens found in the main caving areas of Britain.
» Download Key – PDF-File, 505.3 KB
|AREA||NOTES ON ORGANISMS|
|Peak District, Yorkshire Dales, Northern England, Scotland and mines in North wales||Niphargus species are not likely to be encountered in these systems
Gammarus pulex - if the specimen is largish (~10mm) and shrimp-like with eyes present (these might be white like the rest of the animal). Animal is most likely to be white underground but some specimens, especially in cave systems near the entrance, might have a yellow / orange colouration
|South Wales||Niphargus fontanus - Shrimp-like white animal without eyes
Proasellus cavaticus - Aquatic woodlouse-like animal, white, eyes absent
Gammarus pulex might be present in some caves (see note above) and can co-exist with both Niphargus fontanus and Proasellus (e.g. Elm Hole)
|Mendips and Forest of Dean||Niphargus fontanus, Proasellus cavaticus and Gammarus pulex; can co-exist (e.g. Barnes Loop in Swildon's Hole)|
|Devon||Niphargus glenniei - Small (3mm), white shrimp-like animal, without eyes
Niphargus aquilex - Larger (8mm), white, shrimp-like animal without eyes, elongate thin body shape
Both these species can co-exist (e.g. Rift Cave, Pridhamsleigh Cave)
As discussed in the section on hypogean Crustacea ecology, it is now widely believed that only Antrobathynella stammeri exists in Britain and Ireland. However, future work might find that Bathynella natans does occur in the British Isles and subsequently the early records of Bathynella natans cannot be entirely discounted.
(drawing from Gledhill et.al. 1993, after Thienemann)
Both Antrobathynella stammeri and Bathynella natans are very small, eyeless crustaceans, approximately 1mm long and 0.1mm in diameter. They are more or less colourless with long, thin bodies, highly developed to suit the interstitial habitat in which they are generally recorded. The body is elongate with 14 trunk segments (8 thoracic and 6 abdominal) and the head is longer than broad. Each of the thoracic limbs, with the exception of the last, is two-branched. All but the first and last abdominal segments are without appendages. The 1st antenna is un-branched, the 2nd has a small branch. The two species are separated by the number of spines (5 – 7 in Bathynella and 4 in Antrobathynella) on the uropodal protopod and the number of teeth (7 in Bathynella and 6 in Antrobathynella) on the mandible.
Bathynellids were first recorded in Britain in 1927, when A.G. Lowndes collected two specimens (recorded as Bathynella natans) from a tub which caught drippings from the roof of one of the tunnels in Pickwick Quarry, one of the bath stone quarries near Corsham, Wiltshire. Bathynella natans has since been recorded from a spring and riverine gravels in Devon; a spring-fed cattle trough in Berkshire; and water pumped from alluvial gravels on the Thames near Pangbourne, Oxfordshire. This first group of early records were all listed as Bathynella natans and although material was not available for confirmation it is thought that they were probably mis-identified Antrobathynella, although without confirmation, the existence of Bathynella natans in Britain cannot be entirely discounted. All modern (post 1960) records have been positively identified as Antrobathynella stammeri and include: boreholes in Yorkshire and Devon; pools and streams in White Scar, Skoska and Great Douk caves (Yorkshire); riverine gravels on the rivers Plym (Devon), Tees, Lune, Liza, Derwent, Duddon (Cumbria), Skirfare (Yorkshire) and Lathkill (Derbyshire); and alluvial gravels on the Altquhurbum Burn, a tributary of the River Endrick in Stirlingshire, Scotland. The species was recently (2012) recorded from the Ogof Draenen cave system in South Wales and is also known from the interstitial habitat on the River Flesk in Killarney, the only record from Ireland. Outside of Britain Antrobathynella stammeri is known from Germany, Austria, Italy, Romania and the Czech Republic and was recently discovered on the island of Jersey.
|Antrobathynella stammeri from the
River Skirfare, Yorkshire,
Photo courtesy of Mark Dunscombe
Most of the records are from the interstitial habitat and include areas previously glaciated. Bathynella / Antrobathynella is likely to have survived beneath the ice in sub-glacial refugia. Bathynellidae are probably widespread in the interstitial of the phreatic or permanent water table. The recorded distribution in the British Isles is wide but disjunct and it is likely that the bathynellids have been overlooked and under-recorded.
Proasellus cavaticus (Leydig, 1971, sensu Henry, 1970)
In appearance the Asellidae (freshwater Hoglice) look like aquatic woodlice, with Proaselluscavaticus being easily separated from the epigean Asellus aquaticus and Proasellusmeridianus by its lack of eyes and pigment. The two latter species occasionally turn up in allogenic streams in caves, washed in from the surface.
In Gledhill et. al. (1993) Proasellus cavaticus is named as Asellus cavaticus. Henry & Magniez (1970
& also see 1983) split the genus Asellus, raising the sub-genera Proasellus, Dudich, containing the species Asellus cavaticus and Asellus meridianus, and Conasellus, Stammer, containing Asellus communis, to generic level [Conasellus communis has since been moved to the genus Caecidotea (Packard, 1871)]. This proposal has been widely accepted in Europe. At the time of the publication of the FBA key there was some debate amongst the authors but it was decided to retain the single genus Asellus (Gledhill pers. comm.). Most British workers on the hypogean Crustacea use the name Proasellus cavaticus, in line with their European counterparts.
Proasellus cavaticus was first collected from the Town Well at Ringwood, Hampshire by D.E Lucas in 1925. It is widespread in caves in the Mendips and South Wales but has also been recorded from various interstitial and groundwater sites in southern England and Wales. These sites include: the upper reaches of the Little Stour River and Dartford in Kent; the Corsham stone quarries, Wiltshire; water cress beds and boreholes in Dorset; Spratts Barn Mine, Oxfordshire; boreholes in the Cotswold Hills of Gloucestershire; and several springs, boreholes and rivers in South Wales.
British Proasellus cavaticus have two distinct size morphs. A smaller form (approx. 4mm to 6mm) is common in the vadose zone of Mendips caves, whilst the larger (approx. 8mm to 11mm) morph is found in the South Wales caves and the phreatic zone of Mendip caves such as Wookey Hole and the Cheddar River Cave. The Ringwood specimens and those recently collected from boreholes in Dorset are of the larger morph. It has been suggested that the two morphs might be distinct cryptic taxa (morphologically almost identical but genetically different). However a recent molecular analysis of the two size morphs and comparison with European specimens by Christophe Douady of the University of Lyon have shown them to in fact all be one species, rather than a group of cryptic species, although the largest British specimens appear to be much larger than the European specimens examined at Lyon so far. The reason behind the occurrence of the smaller size morph in the vadose zone of Mendip caves requires further investigation.
Crangonyx subterraneus (Bate, 1859)
Crangonyx subterraneus, together with Niphargus species are members of the Amphipoda and show the typical “shrimp-like” appearance of the group. Collectively both Crangonyx subterraneus and the Niphargus species are often colloquially known as ‘well shrimps’ or ‘cave shrimps’.
|C. subterraneus from S Wales.
Photo courtesy of Jules Carter
C. subterraneus is not easy to separate from Niphargus without microscopic examination. The main differences are that in the former the gnathopod hands are longer than broad and the telson is only shallowly emarginated posteriorly. In Niphargus the telson is deeply cleft and the hands are about as broad as long. Glennie (1956) observed that live Crangonyx subterraneus kept in captivity crawled upright in silt and never swam or lay on their side, unlike live Niphargus. A similar behavioural difference is exhibited between epigean Crangonyx pseudogracilis and Gammarus pulex. C. subterraneus is easily separated from C. pseudogracilis (a naturalised species introduced from North America), the only other Crangonyx in Britain, by its lack of eyes and colouration. Specimens of Crangonyx subterraneus generally tend to average 4 to 6mm in length.
|C. subterraneus from the Little Stour River, Kent|
Crangonyx subterraneus was first described by Bate (1859) after examination of specimens collected (along with several niphargids) by the Reverend A. R. Hogan from a well at Ringwood, Hampshire. It has since been recorded from interstitial riverine gravels, wells, boreholes and springs from Kent in the east to Dorset, Devon, and Glamorgan in the west. It is only known from three caves, Gough’s cave and Reservoir Hole, both in the Cheddar Gorge on the southern flank of the Mendip Hills and from the lake in Ogof Pant Canol, part of the Ogof Ffynnon Ddu system in Breconshire. The distribution of the species seems to correlate with aquifers in chalk or limestone. Important groups of records include those by: Terry Gledhill from the Waterston Cress beds in Dorset from 1969 to 74; Paul Wood from the spring head of the Little Stour River in Kent and by Three Valleys Water staff from boreholes and wells in Hertfordshire, Buckinghamshire and Bedfordshire. There are important recent records (2011) for the species from a well in an outcrop of oolitic limestone at Beer in south-east Devon, as well as another important record from riverine gravels in the Afon Lluestgota (part of the Rheidol catchment) north east of Aberystwyth, sent in by staff from the Environment Agency. This location is well north of the Devensian limit and has important implications for the distribution of the species. However, no specimen was retained for confirmation and there is some doubt over the correct identification.
Outside of Britain Crangonyx subterraneus is known from western and central Europe.
|Microniphargus leruthi from interstitial gravels on
the Dripsey River at Dripsey Bridge, County Cork.
Prior to 2006, Microniphargus was unknown from Britain and Ireland and was previously thought to have a very limited area of distribution, between the Ardennes and the northern Rhine region. It has been recorded at various sites in Luxembourg, Belgium (including Engihoul Cave and wells near Liège (Karaman & Ruffo, 1986)) and western Germany (including caves and wells / boreholes). The discovery of Microniphargus in Ireland and Britain has great significance in our understanding of the distribution of the stygobitic Crustacea and the recent reports represent a big jump in the known distribution of the species from the Ardennes of Belgium. County Cork and the British records lie to the south of the last glacial limit, whilst Counties Clare and Louth lie far to the north. The Irish and British specimens match the described morphology of Microniphargus and a morphological comparison with European material from the Berlin Museum has been carried out by Terry Gledhill of the Freshwater Biological Association (Knight & Gledhill, 2010). However, detailed molecular (DNA) studies are required to ascertain if the Irish and British material is indeed Microniphargus and not a 'cryptic' species new to science; a project is currently underway to address this.
Microniphargus leruthi has specific characters, such as its small size (1-2mm) and the shape of the mandiblular palp, telson and gnathopods that set it apart from other genera in the family Niphargidae (Karaman & Ruffo, 1986). The third segment of the mandidular palp does not have a fringe of small bristles. The gnathopds are slightly longer than broad and appear rather rectangular. The telson is as long as wide, has a V-notch (as opposed to a cleft / split in other species) to about halfway and each lobe ends in a single spine. Other differences include the pleopods with two branches and the laccinia of the maxilla with a maximum number of seven spines. These features are illustrated in the sketches below.
The Niphargus group has representatives throughout Europe. Its members are eyeless and colourless and bear a resemblance to the ubiquitous freshwater shrimp (Gammarus pulex) of surface waters. They occur in a variety of subterranean aquatic habitats where they are generally believed to be saprophagous (i.e. they feed on animal and plant derived detritus). However, they can be predacious on other invertebrates if the opportunity presents itself,
|Niphargus aquilex in Rift Cave, Devon|
Niphargus aquilex was first discovered in 1853 by Professor Westwood, who obtained specimens of a subterranean amphipod from a well near Maidenhead, Berkshire. He described them initially as being Niphargus stygius, a species then known from continental Europe. However, in 1855 Schiődte re-examined the material and described them as a new species, Niphargus aquilex.
On average N. aquilex tends to have a more elongated body shape in comparison to other Niphargus and generally most specimens tend to be larger than N. kochianus and N. glenniei. Most British specimens of N. aquilex average 5 to 8mm in length, although much larger specimens up to 12 and even 15mm have frequently been recorded. One of the main features that differentiate N. aquilex is the rounded posterodistal angles on epimeral plates 2 and 3, although this is not so pronounced on juvenile specimens. Lateral spines on the telson lobes and an obtuse palmar angle on the propodus of gnathopods 1 and 2 distinguish this species from N. kochianus. Hartke et al. (2011) recently carried out a comparative examination of specimens in the Niphargus aquilex / schellenbergi / fontanus group. N. schellenbergi bears a superficial resemblance to N. aquilex and in the past the two have been considered sub-species (cf. Niphargus aquilex aquilex; N. aquilex schellenbergi). The presence of a single spine on the dactyl of the gnathopods seems to differentiate N. aquilex from the other two species. Other diagnostic features were included in the paper, although there does seem to be variation in British specimens from those examined, primarily in the number of spines on the posterior margin of the basis of pereopod VII. N. schellenbergi is known from France, Germany, Belgium and the Netherlands and Hartke et al. (2011) highlighted the fact that many specimens from the Hartz Mountains of Germany previously identified as N. aquilex were in fact N. schellenbergi. A re-examination of several larger specimens of British N. aquilex was carried out by Knight and Gledhill, with all British specimens conforming to aquilex morphology. Molecular studies at Hull University have recently highlighted the presence of a distinct N. aquilex clade in Britain with close genetic ties to N. schellenbergi, which might represent a ‘cryptic’ taxon.
|Specimens of N. aquilex from the winterbourne section of the River Till, Wiltshire||Photos courtesy of Chris Proctor|
Niphargus aquilex is the commonest British niphargid, occurring in wells, interstitial gravels and other subterranean waters in southern England and Wales. It has been recorded from many locations, mostly south west of a line drawn from the East Coast of Kent to the Wirral Peninsula in Cheshire, with most records concentrated in the south. There are modern records from Lincolnshire, South-east Yorkshire and northern Wales, including Anglesey and very old records exist of the species from Hartlepool, County Durham (1893) and Henwick, Worcestershire (1863). This latter group of locations is north of the Devensian limit and imply that they might have been re-colonised by N. aquilex after the last ice age (see section on hypogean Crustacea ecology). N. aquilex is probably widely distributed in ground water and is liable to be found where this reaches the surface (e.g. springs) (Gledhill et.al., 1993). It has been found in low-lying ground (e.g. from under the Sphagnum moss cover of a mash near Wellington) where the soil-water zone is continuous with the phreatic, or ground-water, zone and it is thought that, in England at least, the species may be beginning to invade the soil-water zone (Glenniei, 1956). N. aquilex is occasionally collected whilst kick sampling for benthic macro-invertebrates in rivers and streams and is likely to be widespread in the hyporheic zone of many watercourses.
N. aquilex is more commonly found in groundwater sites (e.g. wells, springs, aquifers and riverine gravels) than in caves and there are few records from the latter. It has been recorded from Rickford Cave in the Mendips, Paviland Cave on the Gower Peninsula, Ogof y Pebyll near Bridgend and from Agen Allwedd, Breconshire, although this latter record is thought to be a mis-identification of Niphargus fontanus. It is common in Holwell Cave in Devonian Limestone in the Quantock Hills, Somerset and frequently occurs in caves in Devon, also in Devonian Limestone. Holwell Cave and the Devon caves differ from most other British caves in their Devonian geology. However it is thought that the main reason for N. aquilex’s presence in caves in the far south west might be the absence of Niphargus fontanus, the most commonly occurring cavernicolous Niphargus, from this area. Competition with the robust and relatively large N.fontanus might exclude N. aquilex from caves in the Mendips and South Wales, although the two species are often recorded together at groundwater sites such as the Town Well at Ringwood and Waterston cress beds. N. aquilex sometimes occurs with Niphargus glenniei in Devon caves, even sometimes in the same pools. However, N. glenniei is much smaller and less likely to be a competitive threat.
As well as mainland Britain and the Isle of Anglesey mentioned above, Niphargus aquilex has also been recorded from the Isle of Wight and Jersey, Guernsey, Sark and Alderney in the Channel Islands. It is also known from central and southern Europe, including Italy and the Balkans and is one of the most widely distributed species in Europe.
Niphargus fontanus was originally described by Bate (1859) from specimens collected from Ringwood, Hampshire and Corsham, Wiltshire. Since the original description is rather short and poorly illustrated, Gledhill (1980) designated and re-described the lecotype from one of two syntypes held at the British Museum of Natural History. Niphargus fontanus is differentiated from Niphargus kochianus by lateral spines on the telson lobes and an obtuse palmar angle on the propodus of gnathopods 1 and 2. The propodus of gnathopod 2 is distinctly larger (longer and wider) than that of gnathopod 1, a key distinguishing feature for N. fontanus. Epimera 2 and 3 have a sub-rectangular posterodistal angle. Specimens generally tend to be 8 to 10mm in length, although smaller specimens have been recorded from interstitial habitats and those from caves and chalk aquifers have been noted to be significantly larger, up to 15mm. Larger specimens tend to be considerably more ‘robust’ in shape in comparison to Niphargus aquilex of similar length.
|N. fontanus Photos courtesy of Phil Chapman|
Away from mainland Britain, N. fontanus has also been recorded from two wells on the outskirts of St. Hellier on Jersey. On the continent it is known from eastern France, Belgium, Germany and Austria.
Specimens of N. fontanus from cave habitats and chalk aquifers generally tend to be larger and more robust than those from interstitial sites and other rock strata. It is believed that this is possibly a response to the larger groundwater conduits found in karst (limestone and chalk). It has also been suggested that food sources might be more available in cave habitats. Across Europe N. fontanus consists of four distinct lineages, two of which are found in Britain and one of which is endemic (McInerney et al., 2014).
Niphargus glenniei was first observed on 19th April 1948 in Pridhamsleigh Cave, near Buckfastleigh, Devon by Brigadier E.A. Glennie of the Cave Research Group, in company with Mary Hazleton, who actually captured the first specimen. G.M. Spooner, of the Plymouth Marine Laboratory examined these first specimens and described them as a new species (Spooner, 1952) named after Glennie himself.
Niphargus glenniei can usually be easily separated from the other British Niphargus by virtue of its much smaller size. Niphargus glenniei attains sexual maturity at 2.5 to 3mm long (most specimens tend to be 3mm in size), whilst other British Niphargus species are sexually mature at a minimum size of 4 to 6mm (see individual descriptions for approximate adult lengths). The Irish species, Niphargus wexfordensis and male Niphargus kochianuskochianus are the nearest species from the British Isles to Niphargus glenniei in size, attaining sexual maturity at about 3 and 4mm respectively. Other distinguishing features are the lack of spines on the telson lobes; rounded palmar angles on the gnathopods (gnathopod 2 propodus larger than that of gnathopod 1); a reduced number of D-setae on mandible palp article 3; and on uropods 1 and 2 the outer ramus is distinctly shorter than the inner ramus. This latter feature is probably the easiest to see under a microscope and is the most obvious way of identifying the species.
|N. glenniei in Reed's Cavern, Buckfastleigh, Devon|
Schellenberg (1938) established the genus Niphargellus, containing the European species Niphargellus arndti and Niphargellus nolli, primarily on the basis of reduced setation of the mandibular palp. Although Spooner (1952) and others considered Niphargellus to be invalid, It was retained and some authors (e.g. Glennie, 1967; Gledhill et.al. 1976; Karaman & Ruffo, 1986) formerly placed N. glenniei in Niphargellus. However another species, Niphargus boulangei also has a reduced number of setae, as does the relatively recently discovered Niphargus wexfordensis from Ireland. Karaman et. al. (1994) therefore concluded that the genus Niphargellus should only be retained for Niphargellus arndti and Niphargellus nolli and that the Niphargus glenniei group (including N. boulangei and N. wexfordensis), with low numbers of D-setae, represents a link between the genus Niphargus, with a fringe of numerous D-setae and the genus Niphargellus with no D-setae. Thus N. glenniei is now considered to be a member of the genus Niphargus (Karaman et. al. 1994 and Gledhil et. al. 1993).
|N. glenniei from Fishcombe Quarry Cave, Brixham, Devon.
Photo courtesy of Chris Proctor
Glennie (1967) states that "Niphargus glenniei is a highly interstitial form", as suggested by its thin body and small size and that the species is "frequent in the Pridhamsleigh and Buckfastleigh caves in the Devonian limestones in South Devon, where its true home is in the very disturbed rock."
Until recently, the county of Devon was thought to be the only locality world-wide from which Niphargus glenniei is known. It is believed to be endemic to England and was given a Red Data Book K and 5 (Insufficiently Known and Endemic) conservation status by Bratton (1991). It has recently (2007) been accepted on the list of British Biodiversity Action Plan (BAP) species and in addition to the Devon BAP, is on the local BAPs for the Torbay, Teignbridge and Dartmoor areas, which include some of the caves and wells in which it occurs.
|N. glenniei from Fishcombe Quarry Cave, Brixham, Devon.
Photo courtesy of Chris Proctor
Within the North Devon vice-county, it has been recorded from Napps Cave, near Berrynarbor and more recently (2010 and 2009) from three wells, four springs and two boreholes, in the Ilfracombe area in the north and near Tiverton in the east, fairly close to the Somerset border. However, by far the majority of the Devon records are from the South Devon vice-county and include: mines, springs, wells, a borehole and amongst riverine gravels in a spit on the upper reaches of the River Plym. These sites are distributed from the Tavistock and Plymouth areas in the west to the village of Kenton, close to the Exe estuary in the east of the county. Niphargus glenniei is also known from many of the caves in South Devon, with recent (post 1998) discoveries in the Chudleigh, Torquay, Plymouth, Brixham and Berry Head Devonian limestone outcrops.
In late 2000, N. glenniei was discovered in a well in granite near Land’s End and investigations since 2000 have found the species at five other wells in West Cornwall. In early 2011 the species was recorded in Carnglaze Caverns, an underground slate mine near Liskeard and another well in East Cornwall, with an additional record from a borehole near Wadebridge added in 2013. The species is found in groundwater aquifers ranging in character from Devonian Limestone to the acidic granite of Dartmoor and West Cornwall, with other records in igneous tuff (Ilfracombe area) and to a lesser extent, slate and other strata.
First described by Bate (1859) Niphargus kochianus from a single specimen collected from a pump in a house at Ringwood, Hampshire. In the early 1930s Schellenberg (1932; 1933) added two sub-species, one from Belgium and France and one from Ireland (Niphargus kochianus irlandicus), [formerly English N. kochianus was also described as a sub-species (cf. Niphargus kochianus kochianus) see below] upon examination of the first male specimens of the group obtained. British specimens of male Niphargus kochianus were not recorded until 1970, from the Waterston cress beds by Gledhill (1977) (although there is a dubious record of a male specimen from St. Cuthbert’s in 1966). It is thought that the hitherto rarity of records for the males was due to the dominance of females in most collections and the fact that the two sexes are very similar morphologically. Sexual dimorphism is not evident in the uropods, as it is in most niphargids, but in the length of the carpus of gnathopod 2, which is distinctly longer than the propodus in females, a key diagnostic feature for the species. Adult males are also on average smaller, about 3 to 4mm (mean 3.1mm in Stock & Gledhill, 1977)), in comparison to females which average 4 to 6mm (mean 3.9mm in Stock & Gledhill, 1977), the reverse being true for most other gammarids. Stock & Gledhill (1977) raise the interesting question as to whether the low percentage of males in certain populations and their smaller size might be due to the possibility of parthenogenesis occurring in the kochianus group, with the possibility of sex-reversal occurring in protandrous individuals.
The newly discovered British males differed from the descriptions of European male. Niphargus kochianus and it was thought that the European specimens might actually belong to a different sub-species. Stock & Gledhill (1977) revised the taxonomy of the Niphargus kochianus group in North West Europe. Specimens from the Netherlands and Belgium, previously thought to be Niphargus kochianus, were re-designated as a new sub-species, Niphargus kochianus dimorphopus, (later elevated to species rank cf. Niphargus dimorphopus), based on the pronounced secondary sexual dimorphism of the male’s second pair of gnathopods, which is feeble in N. kochianus. Another sub-species N. kochianus pachypus (south-eastern Netherlands to southern France) was also re-described and raised to species rank (cf. Niphargus pachypus ). Niphargus kochianus is also very similar morphologically to its Irish congener Niphargus irlandicus (formerly Niphargus kochianus irlandicus). However, recent genetic studies by Hänfling et al. (2008), Arnscheidt et al. (2012) and McInerney et al. (2014) have conclusively demonstrated that N. kochianus and N. irlandicus are not closely related and are quite clearly separate species (see Niphargus irlandicus section below). Stock & Gledhill (1977) and Karaman & Ruffo (1986) consider N. kochianus to be endemic to southern England, though Vonk (1988) and Ginet (1996) record it from France and specimens were recently (2012) collected from the island of Alderney in the Channel Islands, supporting this assertion. The initial results from molecular analysis of these specimens suggest that they are closely related to N. kochianus specimens from southern England (Knight et al. 2015). The Niphargus kochianus group shares many morphological similarities with the Niphargus skopljensis group of species and the whole was regarded by Stock & Gledhill (1977) as a species complex (c.f. the kochianus-skopljensis complex) The skopljensis group includes several species (N. longidactylus, N.petrosani and N. polonicus) formerly regarded as sub-species of the Niphargus kochianus group which are recorded throughout Europe, from the Netherlands to Romania and Russia.
N. kochianus is differentiated from other British niphargids by the sub-acute palmar angle of the propodus of gnathopods 1 and 2 and the acute posterodistal angle of epimeron 3. The telson lobes lack lateral spines, although 3 - 4 distal spines are present. N. kochianus and N. irlandicus primarily differ in the shape of the propodus; an extensive fringe of D-setae on the mandible palp article 3 of N. irlandicus; a single dorsal spine on either side of urosome segment 2 in N. kochianus (3 – 4 spines in N. irlandicus); and the more acute posterodistal angle on epimeron 3 in N. kochianus.
|N. kochianus from the lake in Pen Park Hole, Bristol.|
N. kochianus has been recorded across southern England, from Norfolk and Kent in the east to Gloucestershire (possibly Somerset) and Dorset in the west. It is absent from Devon and Cornwall. There is also a single record from Jersey in 1960 and specimens conforming to the described morphology for the species were collected from Alderney in early 2012. There appears to be a strong correlation between the chalk (Cretaceous Limestone) outcrops and the distribution of N. kochianus. A similar association has been reported by Vonk (1988) in France. Most of the records are from interstitial (alluvial gravels) and phreatic (boreholes and wells) sites with only three records from caves. The single 1966 record from St. Cuthbert’s Swallet, in the Mendips is thought to be a possible confusion with mis-identified Niphargus fontanus. There are two 1951 records from Holwell Cave in the Quantock Hills of Somerset, although recent visits have only found Niphargus aquilex. Niphargus kochianus is present in large numbers, sometimes accompanied by N. fontanus, in the lake in Pen Park Hole, Bristol. This has been confirmed by recent surveys (Knight, 2014). The lake is believed to connect to the phreatic water table and the level has been observed to fluctuate with groundwater levels. It is thought that N. kochianus is predominately an inhabitant of phreatic groundwater.
Niphargus irlandicus (Schellenberg, 1932)
The first Irish niphargid record was from Dublin in 1863 by Professor Kinahan, in an old well sunk in limestone. A second record, in 1899 from a well at Templeogue, Dublin was identified as Niphargus kochianus. Schellenberg (1932) differentiated the Irish specimens as a separate sub-species (Niphargus kochianus irlandicus), which was upheld by Stock and Gledhill (1977). Although the former sub-species N. kochianus kochianus and N. kochianus irlandicus are morphologically very similar [Stock and Gledhill (1977) proposed the retention of sub-specific status for both] the two have been separated from each other by the Irish Sea for at least 10000 years and share no genetic continuity. Recent DNA analysis (Hänfling et al. 2008; Arnscheidt et al. 2012; McInerney et al. 2014) has shown that they are not in fact related and that they last shared a common ancestor some 23 million years ago. It would appear that N. kochianus irlandicus is more related to N. glenniei than N. kochianus kochianus. On the basis of this work Niphargus kochianus irlandicus and Niphargus kochianus kochianus were both elevated to species rank (cf. Niphargus irlandicus and Niphargus kochianus). It would appear that morphology is not always the best method for taxa separation and highlights the importance of DNA studies in discovering “cryptic” species within subterranean ecosystems.
The key diagnostic features for identifying Niphargus irlandicus are described in the section on Niphargus kochianus. The two share a similar scarcity of male specimens within populations and a similar size range. Stock & Gledhill (1977) list males as averaging 4 to 4.5mm and females as 4 to 5.5mm (although mention is made of a larger specimen up to 6mm).
Niphargus irlandicus, along with Niphargus wexfordensis , are endemic to Ireland and are the only two species of Niphargus currently known to be present. N. irlandicus has been recorded from numerous localities across southern and central Ireland, extending from County Kerry and County Cork in the south, as far north as the Dundalk Peninsula (County Louth) on the east coast, the southern border of County Fermanagh and the Carrowmore cave system on the high plateau above the village of Geevagh (County Sligo) in the west. These latter three records are the most northerly for the genus Niphargus in Europe. Arnscheidt et al . (2008; 2012) and Knight & Penk (2010) found it to be by the far the commonest of the three species of niphargid in Ireland. Unlike most other British niphargids, most of these records are within areas fully glaciated during the Midlandian. Costello (1993) suggests that it might be a pre-glacial relict species, having survived beneath the ice in sub-glacial refugia. Arnscheidt et al . (2012) proposed the geothermal refuge hypothesis: geothermally heated waters and springs provided habitats for the Irish niphargids beneath the ice sheets. They also suggested that the northern limit of its distribution was governed by a series of poorly productive aquifers extending north of a line from Dundalk to Sligo, the strata of which provided limited space for habitat and potential dispersal routes. Habitats that N. irlandicus has been recorded from include springs, wells, riverine gravels and caves, the latter mostly in County Clare. It has also been recorded in the bottom sediments of Lough Mask. Both Schellenberg (1932) and Stock and Gledhill (1977) noted slight morphological differences between specimens from Lough Mask and those from caves and wells, although these were not thought sufficient enough to form the basis of a new taxon. However, in light of the recent studies separating N. irlandicus from N. kochianus , some new research into this subject is required. In a recent study of the phylogenetics and phylogeography of N. irlandicus , Arnscheidt et al . (2012) identified three distinct clades in Ireland, which seemed to occupy separate regions. The largest group, lineage 1 was present in the northern counties [Mayo, Galway, Clare, Kildare, Louth and Fermanagh]; lineage 2 comprised a single population in Co. Tipperary; and lineage 3 comprised populations in the southern counties of Waterford, Clare and Cork. There appeared to be some cross-over of lineages in Co. Clare with individuals present from both lineages 1 and 3. Recent surveys of the Irish hypogean Crustacea were carried out in the period 2006 to 2010 by a team headed by Joerg Arnscheidt at the University of Ulster and Knight & Penk (2010).
|N. irlandicus gnathopod|
|N. wexfordensis (drawing from Karman et. al., 1994 'A new subterranean amphipod (Crustacea: Gammaridea: Niphargidae) from southern Ireland, with comments on itas taxonomic position and the validity of the genus Niphargellus Schellenberg.' Zoological Journal of the Linnean Society, 112)|
First recorded from a well in the garden of a house at Kerloge, County Wexford in 1980, this was the only known location for this endemic Irish species until 2006, when it was discovered at a second site in County Wexford by Dr. J. Arnscheidt of the University of Ulster. It was then discovered at another four sites in a survey of Irish sygobitic Crustacea in springs and caves carried out by Knight and Penk (2010). These sites included a spring in County Wexford; a spring in County Kilkenny; Central Cave, in the Carrigacrump Quarry, County Cork; and Polldubh Cave on the Burren, County Clare. N. irlandicus was also recorded with N. wexfordensis in the Kilkenny spring and Central Cave. The results of this survey led to the re-examination of specimens, identified as Niphargus kochianus irlandicus, collected from the Doolin River Cave (Co. Clare) in 2005 and the discovery that one of the smaller specimens was actually Niphargus wexfordensis. Further work in March 2009 found N. wexfordensis in a third cave on the Burren (Doonyvarden Cave), along with Microniphargus. Arnscheidt et al. (2012) extended the known northern distribution of the species when they recorded it in a borehole at Curragh, Co. Kildare. These records show that N. wexfordensis is more widespread than previously thought and also raises some questions on the identity of some of the records in the 1960s and 70s from caves on the Burren. At the time N. irlandicus was the only species known to exist in Ireland.
|Niphargus wexfordensis from a spring in County Kilkenny.|
Niphargus wexfordensis was described by Karaman et. al. (1994), who noted its similarities with Niphargus glenniei, primarily a reduced number of D-setae on article 3 of the mandible palp, a small size [in Karaman et al. (1994) the female holotype was 4.3mm and the male 3.2mm (although it was thought to be immature); recent specimens have been measured up to 5mm] and the outer ramus distinctly shorter than the inner on uropod 2 (although the rami are sub-equal on uropod 1). It differs from N. glenniei in the telson being cleft to almost half its length (three-quarters in N. glenniei and N. irlandicus), with each lobe bearing 3 distal spines and a pair of plumose setae (no spines and 3 distal setae in N. glenniei) and differences in the setation of the mandible palp articles 2 and 3. The main features that separate the species from N. irlandicus include the telson cleft and mandible palp, mentioned above and the more rounded shape of the gnathopods, with gnathopod 2 propodus normally larger than that of gnathopod 1. This latter feature means that superficially N. wexfordensis resembles small specimens of N. fontanus.
|Niphargus wexfordensis, photographed under a blue filter
(specimen from a spring in County Kilkenny).
|Niphargus wexfordensis , details of anterior and gnathopods (photographed under blue filter, specimen from a spring in County Kilkenny)|