An annotated check-list of British Pleistocene, Holocene and modern freshwater ostracods

A revised check-list of British Pleistocene, Holocene and Recent freshwater ostracods is given, and notes provided on the taxonomy and occurrence of some rare and newly-reported species. Stenocypria fischeri (Lilljeborg. 1883) and the hypogean species Pseudocandona cf. eremita (Vedjvosky, 1882) and Pseudocandona breuili (Paris, 1920) arc reported from Britain for the first time.


INTRODUCTION
Over recent years there has been renewed interest in freshwater ostracods, particularly because of their potential in palaeolimnological and palaeohydrological studies (see reviews by Delorme, 1989;De Deckker & Forester, 1988: Carbonel et a / . 1988Holmes, in press). This increase in ecological interest has been accompanied by a spate of taxonomic and systematic research that has done much to increase our understanding of evolutionary patterns and processes in freshwater Ostracoda. Some freshwater ostracod lineages are evolutionarily dynamic, and divergence within rhe Holocene has been demonstrated for at least onc cluster of lake-specific taxa (Martens, 1990). It is possible that the examination of ostracod valves in extended lake corm (which often cover periods of several thousands of years) may prove to be a powerful tool to the evolutioi-iary biologist (Evans Rr . However, advances in ostracod palaeobiology d o require continuity in systematic nomenclature.

A BRIEF HISTORY OF BRITISH OSTRACOD ST UDI E,:S
Some of the key works in ostracod taxonomy were based on studies o f the British and Irish faunas during the last century, notably through the work of G. S. Brady and colleagues (e.g. Brady & Robertson, 1869;Brady & Norman, 1889;Brady, 1910). As a result, comparatively comprehcnsive check-lists of the faunas of both Britain (Scourfield. 1904) and Ireland (Norman, 1905) were available within the first years of this century. Subsequently. interest in native ostracod faunas waned, and scientific attention was turned to the description of species from overseas. Some workers continued to study British freshwater species, notably P. F. Holmes, A. G. Lowndes, G. Fryer and H. M. Fox, however most had a broad interest in freshwater Crustacea, rathcr than a specific interest in ostracods. Hence, prior to the 1980s. there were remarkably few published contributions, and no substantial body of work accrued. Despite this, J. E. Robinson's Pleistocene and Holocene studies continued to document ostracod faunas, as occasionally have archaeological (e.g. Griffiths & Mount, 1993) and modern synecological works (e.g. Ham, 1982).
An updated check-list of freshwater Ostracoda was made as part of the Institute of Terrestrial Ecology's attempt to compile a complete listing of British freshwater animals (Maitland, 1977). This was not based upon the work of a single individual, but gleaned from a variety of sources, largely without reappraisal. More recently, a new faunal work on modern British freshwater ostracods has been published as part of the Linnean Society's 'Synopses of the British Fauna' series (Henderson, 1990). Unfortunately, this important benchmark was delayed in press for almost five years (Henderson, pers. comm.) and, as a result, over 30% of the specific and generic nomenclature used by Henderson had been superseded by the time of publication. The undesirable result is a loss of continuity with current European taxonomic usage (e.g. Wouters. 1989: Meisch et al. 1990. With the increasing interest in the group by both palaeoecologists and freshwater biologists, it seems timely to provide a check-list of the British species that includes not only recent revisions, but also records of Recent species omitted by Henderson (1990), plus a small number of species that are thus far known only from Pleistocene and Holocene contexts.

NOTES ON SOME OF THE SPECIES
Changes of generic assignation and specific nomenclature have come about as the result of formal revisions, the details of which are beyond the scope of this account. Key works include those of Broodbakker (1983), Carbonnel (1963, Colin & Danielopol (1980 Martens (1989Martens ( , 1992 and Meisch (1984Meisch ( , 1985Meisch ( . 1991. Some species d o require additional comment. however. Cyprirfopsis hamberi was originally described from a spring in Cornwall by Hendcrson (1986). Professor T. K. Petkovski (pers. comm.) initially suggested the possible synonymy of C. hamheri with C. brincki Petkovski, 1963, described from wells in the Azores and also known from Germany, Portugal and Macedonia (Petkovski;1963). We examined type material of C. bamheri lodged in the collections of the Natural History Museum in London (BMNH) and reached a similar conclusion. More recently, Petkovski et ul. (1993) have shown C. hrincki to be a junior synonym of C. lusatica Shaffer, 1943, and the synonymy of C. humheri has been confirmed by Dr. C. Meisch of the Natural History Museum of Luxemburg (Meisch, pers. comm.).
Eucypris anglicu was posthumously described as a British endemic by Fox (1967) from sites in Buckinghamshire and Hertfordshire, but has since only been reported as a single specimen from Hampshire (Ham, 1982). Syntypes are maintained in the BM(NH)'s Fox Collection (accession nos 1967.4.3.1,2,3,4), the material consisting of four sealed microscope slides bearing valves, two intact individuals, and intact specimens decalcified in potassium hydroxide. All are mounted in glycerine jelly or euparal. These specimens compare well with illustrated descriptions of E. crassa in Klie (1938) and Sywula (1974), although are a little larger than usually cited (i.e. 2.2 mm). At our request, Professor T. K. Petkovski has re-examined material of E. anglica originally sent to him by Fox, and concluded that the species is indeed distinct. We therefore maintain E. anglica on the British list, although reinvestigation of ncw material of this species would be welcome.
Ilyocypris hiplicata is well-known in Quaternary palaeontology, and has been recorded in the modern faunas of Canada (Delorme, 1970) and France (Meisch et ul., 1990). The status of the species has long been the source of debate; Scourfield (1904) stated that 1. hiplicata was common in Britain, although it seems possible that he may have been confused between I. biplicata and 1. gihha. Sywula (1974) lists 1. hiplicata as a subspecies of I. gihba. Palaeontologists have long accepted I. hiplicata (sensu Diebel & Pietrzeniuk, 1969: pl 7, figs 1-3), and Van Harten (1979) provides a valve-based diagnosis of the species. Ilyocypris hiplicata is a bland ilyocypridid, in which surface ornamentation is reduced. The carapace is sub-rectangular, posteriorally and anteriorally rounded, and with ventral and posterior margins running almost parallel. In Britain the species has often been recorded at Pleistocene sites, and we have material from Holocene deposits at West Overton in Wiltshire (Griffiths & Mount, 1993). As soft-part diagnosis remains elusive (Meisch, 1988), it would seem that 1. gibha and I. biplicata would benefit from examination by either molecular or genitalia-based taxonomic techniques (cf. Martens, 1991). Until such a time as they can either be synonymized or verified, it seems prudent to maintain I. biplicata as a valid species.
Western European species of Potamocypris have been extensively revised by Meisch (1984Meisch ( , 1985 and the nomenclature used here differs somewhat from that of Henderson (1 990). Potamocypris arcuuta was first recorded in the modern British fauna by Griifiths & Evans (1992) from a temporary, groundwater-fed pool in Hampshire. Since that time we have also found the species amongst air-dried material from Regent's Park Lake, London (leg. J. E. Robinson). The species is also known from British late Devensian and Holocene deposits as P. maculata Alm, 1914 (see list of synonyms in Meisch, 1985). Eucypris elliptica. This is one of Britain's less well-known species; Henderson (1990) knew of no definite locations for E. elliptica in the UK. In December 1990, we collected two females from the shallows of Llangorse Lake in the Brecon Beacons National Park, Wales, and Professor D. D. Williams has recently provided further specimens collected from the Island of Bardsey off the North Wales coast. Eucypris lilljeborgi. Again, Henderson (1990) knew of no definite records for this 'exceedingly rare' species, although E. cf. lilljeborgi had been reported from Holocene tufas (Preece Willing, 1985). We have since found E. lilljeborgi living in great numbers in a run-off and rain-fed, grassy, seasonally-inundated meadow adjacent to a Phrugmites-rich pond at Thornhill in Cardiff. Eucypris lilljehorgi first appears when the habitat is inundated in October or November, and then seems to breed continuously until the site dries out in early summer. The species rarely occurs in the reed beds which border the inundated grasses, and males are absent. Carapace length is more variable than usually believed; we have collected gravid females ranging from 1.42-1.88 mm long, although clearly identifiable as E. lilljeborgi on the basis of soft-part anatomy. Trajancypris serrata. There has been considerable confusion over the taxonomic status of denticulate eucypridines. Some are assignable to Prionocypris serrata (Norman, 1861) of which we have modern and Holocene material from the Test Valley, Hampshire. Martens (1 989) erected genus Trajancypris to accommodate subclavate eucypridines with pronounced lists and selvages on the anterior inner margins, including Eucypris serrnta G. W. Miiller, 1900 and E. clavata, the latter having often been recorded from the Pleistocene as Sclerocypris? clavata prisca Diebel & Pietrzeniuk, 1969. Because of the confusion over nomenclature, it now seems almost impossible to say with confidence which denticulate eucypridine was actually meant by many earlier authors. Hence, we provisionally maintain T. serruta in the British check-list, despite having seen neither subfossil or modern material. Paralimnocythere spp. There has been some confusion over the correct specific assignation of non-Balkan species of Paralimnocylhere, now resolved by Martens (1992). Subfossil British material has usually been referred to P. compressa or P . cf. dieheli. Parulimnocythere compressa is known from Mid Pleistocene, late Devensian and Holocene deposits in Britain, although it has not been collected alive for over a century (Martens, 1992). Paralimnocythere ciieheli was originally described from Macedonia (Petkovski, 1969) and a variant, Parulimnocythere cf. diebeli, was described from the German Mid Pleistocene (Diebel & Pietrzeniuk. 1978: fig.2, pl. 52, figs 8-11), Paralimnocythere cf. dieheli has been reported from late Devensian deposits at Kildale, Yorkshire (Keen et al., 1984). Paralimnocythere relicta is only known from the modern fauna, having been reported from Hampshire by Henderson (1990). Fabaeformiscandona siliquosa. This is an unusual species which appears to be a British endemic. Some authors have doubted this: Nuchterlein (1965): 246) believed F. siliquosa to be synonymous with F. caudata. Henderson (1990) maintains F. siliquosa as a valid species, listing several sites in the New Forest of Hampshire. We have also collected F. si/iquosa from permanent ponds in the New Forest arid cornpared it with specimens of F. caudutu from France (i'eg. P. Marmonier). The two species appear very different, and we have retained them both as distinct species. Candona lactea was reviewed by Brady (1910) and retained as a valid species by Henderson (1990). Although we have not examined type material of this taxon, we havc collected material that appears similar to C. lactea, but have never encountered mature individuals. We therefore maintain C. lactea in the British list until formal revision is made, but believe that it may be a synonym mistakenly erected upon juvenile material of another species. Further investigation is required to validate or deny this, suggestion. Pseudocandona elongata was initially described from Lakes Windermere and Ohrid (Holmes, 1937) although no type material was nominated, and none has been located (Henderson, pers. comm.). Petkovski (pers. comm.) has failed to record the species despite many years collecting at Lake Ohricl. Within recent years P. elongata has been reported from Lake Windermere by Horne et al. (1990), but subsequent collections have failed to provide further specimens (Horne, pers. comm.). This species also requires further investigation before it can be validated.
Candona lozeki has been reported from the British Holocene (Willing, 1985: Mount, 1991 and from the Mid Devensian (Gibbard et al., 1981), whilst locations for C. tricicatricosa are all Mid Pleistocene. Fuhrmann (1991) has suggested that C. IozekiC. tricicatricosa are synonymous. If this is the case, this would remove the stratigraphic value of both taxa. Pseudocandona breuili was first described from a cave in Spain (Paris, 1920) and, as Candona breuili, is known from the German Quaternary (Diebel & Pietrzeniuk, 1984) and the Belgian Holocene (Van Frausum & Wouters, 1990). Definitive determination of this species is difficult without soft-parts, although we have collected it in considerable numbers from Holocene deposits at West Overton, Wiltshire and from the Test Valley, Hampshire. It appears that the species lived interstitially, and Danielopol (1978) lists P. breuili as a hypogean species. In some cases at least, it seems that 1' . hreuili has been erroneously identified as the juvenile moult stages of Psychrodromus olivaceus. Pseudocandona eremita is one of a cluster of hypogean ostracods that display a high degree of local endemism, and represent a distinct lineage within Pseudocandona (Danielopol, 1082). These are difficult to identify with precision without soft parts, hence we have cited our taxon as P . cf. eremita. The species occurs in Holocene sediments from West Overton, Wiltshire and Bossington, Hampshire, where it seems to have existed interstitially. Pseudocandonu erernita has a distinctive triangulate carapace, quite unlike any other British candonid. Stenocypria fischeri is only known in Britain from Holocene material from West Overton, Wiltshire (Griffiths & Mount, 1993). Stenocypriu fischeri is illustrated in several European faunal works (e.g. Klie, 1938: 124, figs 416-418: Sywula, 1974. Nannocandona faba. The absence of this species from the fauna of Modern mainland Britain is rather puzzling: the species is quite widespread in Pleistocene and Holocene deposits, furthermore Nannocandona sp. has been reported from Modern Ireland (Douglas & Healey, 1991). As Nunnocandona faba often occurs in interstitial contexts, especially in rivers (Marmonier & Danielopol, 1988), it is possible that it may yet be found in modern Britain, where interstitial habitats remain largely unexplored.

SYSTEMATIC CHECK-LIST
In the following species list, higher-level systematic nomenclature follows Bowman & Abele (1982), and familial nomenclature largely conforms to Hartmann & Puri (1974). The nomenclature of rankings below the familial level conforms to current European usage (Meisch et al., 1990). Taxonomic authorities are drawn from Kempf's index (1980a, b). Species are broadly provcnanced by the following superscripts: P = Pleistocene, H = Holocene, R = Recent. Those taxa which have been recorded in the British fauna, but whose status is here considered questionable, are prcfixed by a question mark. Cyprideis torosu is included, although more typically a species of brackish waters. Family Limnocytheridae Klie, 1938 Sub-family Limnocytherinae Klie. 1938 Genus Leucocythere Kaufmann. 1900 Genus Limnocyrhere Brady, 1867 Leucocythere balrica (Diebel, 1965 Special thanks to D r K. Martens (KBIN, Brussels) who kindly read through an earlier version of this manuscript, made many useful comments and criticisms, and also provided a preprint of his study of Purnlirnnocythere. Thanks also to our many colleagues for their ready help, advice, and assistance. This study was funded by a SERC research grant to J. G. Evans.

Manuscript received August 1992
Manuscript accepted May 1993