Some species of the ostracod genus Bythocythere Sars from British waters

A reappraisal of the genus Bythocythere shows that five species (B. bradyi Sars, B. intermedia Elofson, B. zetlandica sp. nov., B. robinsoni sp. nov. and B. bradleyi sp. nov.) live in British coastal waters. A sixth species, found in Quaternary deposits in Scotland and the North Sea, is not thought to live in this area today. Past records of B. turgida Sars and B. constricta Sars from the Recent of the British Isles are shown to be incorrect.


INTRODUCTION
Species of the genus Bythocythere are commonly encountered living in benthic marine environments around the British Isles. Since fossil examples of these and other Bythocythere species, frequently met with in Neogene and Quaternary deposits in NW Europe, are potentially useful as palaeoenvironmental indicators it is unfortunate that living examples have often been misidlentified.
G.:S. Brady, in his "Monograph of the Recent British Ostracoda" (1 868), recorded two Bythocythtcre species, namely B . constrictu and B . turgidu, originally described by Sars (1866) from Norwegian coastal waters. Subsequent Recent British records of these two species include those of Brady (11870) and Brady & Norman (1889). Sars (1926) described a new species, B . brudyi, from Norway, stating that "this form has been erroneously described and figured by Brady as the male of B . constrictu". Elofson (1941) cast doubts on the validity of ]British records o f B . constrictu and B . turgidu. He suggested that the specimens identified as B . constrictu 'by Brady & Norman were attributable to either B . intermediu Elofson or an undescribed species, and that the form illustrated by Brady (1868 and1870) as B . turgidu could only be: referred to that species with some hesitation.
From our own studies of British material we have determined that five Bythocythere species live around the British Isles: B . brudyi Sars, B . intermediu Elofson, and

MATERIAL
This study is based mainly on material housed in the G.S. Brady collection at the Hancock Museum, Newcastle-upon-Tyne, and in the A.M. Norman and T. Scott collections at the British Museum (Natural History), London. Sources of additional material are acknowledged in the text. Figured specimens have been deposited, as appropriate, in the Hancock Museum (three-part numbers), and in the Zoology Department (two-part numbers) and Palaeontology Department (numbers with the prefix 1 0 ) at the British Museum (Natural History). Order Podocopida Miiller, 1894Family Bythocytheridae Sars, 1866 Genus Bythocythere Sars, 1866 Type species. Bythocythere turgidu Sars, 1866(designated by Brady & Norman, 1889. Diagnosis. Carapace medium to large (0.6-1.0mm long), subrhomboidal, inflated, often with ventrolateral swellings or alar expansions. Posteroventral marginal area compressed. Dorsal margin straight or convex, anterior margin broadly rounded. Ventral margin straight, convex or weakly sinuous. Posterior margin smooth or denticulate, with a subdorsal obtuse caudal process. Dorsomedian sulcus often present. Dimorphic; male proportionally more elongate and sometimes smaller than female. Inner lamella moderately wide anteriorly and posteroventrally, narrower elsewhere. Narrow anterior and posterior vestibula. Marginal pore-canals moderately numerous (twenty to thirty anteriorly), simple, short and irregularly spaced. Hinge lophodont. Normal pore-canals simple, some with raised rims, but mostly recessed, giving valves a pitted appearance. Sieve pores absent. External surface ornamented by a delicate reticulum, often with strong longitudinal elements in the ventrolateral region, which imparts a distinctive "rippled" appearance to the shell.

SYSTEMATIC DESCRIPTIONS
Five adductor muscle scars in a nearly vertical or sometimes arcuate row, with a sixth scar above and somewhat separated from the rest. Frontal scar ovate or reniform. Several other scars may be present above and below the central group. Fulcra1 point weak or absent. Antennula with seven podomeres, each bearing long, thin, flexible setae, except for the penultimate podomere which is devoid of setae. Antenna with four podomeres and three terminal chelate setae; spinneret seta with two joints. Respiratory plate on mandibular palp with up to eight setae. Respiratory plate on maxillula with two pairs of reflexed setae. Legs long, slender. First podomere of first leg (= maxilla) bears a respiratory plate posteroventrally, consisting of four setae, two of which are plumose. Setal formulae of first podomeres of legs: (3(1 +2):2:4), ( l : l : l ) , ( 1 : l : l ) . Male copulatory appendage with a rounded basal capsule, prominent ductus ejaculutorius and a blade-or leaf-like distal process.
Sars described and figured only female specimens of B . bradyi. Wall (MS, 1969) illustrated valves of both sexes from the Recent of Cardigan Bay, but recorded only a single living specimen, a juvenile (A-3). The male copulatory appendage of B . bradyi was first illustrated by Horne (MS, 1980) who found this species living amongst intertidal algae in the Bristol Channel. Distribution. Recent, marine: Norway (Sars, o p . cit.) and British Isles (herein). This is the only British Bythocythere species known to occur in the littoral zone, the others being restricted to sublittoral waters.