Cluthia miocenica sp. nov. (Ostracoda) from the Middle Miocene of southern Poland (Central Paratethys)

Cluthia miocenica sp. nov., the earliest known species of Cluthia Neale, 1973, is described from the upper part of the Middle Miocene (Upper Badenian) of south-east Poland. The occurrence of this species supports the hypothesis of climate cooling during Upper Badenian times in the Central Paratethys and suggests that this region was the birth place of the genus.


INTRODUCTION
The o s l r x o d genus Cluthia Neale, 1973 has been hitherto represented by two species: Cluthia cluthae (Brady, Crosskey & Robertson, 1874) arid Cluthia keiji Neale.. 1985; both recorded from Recent and fossil sediments. They are represented by rare, small and thinshelled individuals easily destroyed and which may be overlooked by micropalaeo-and microneontologists. This 15, presumably the main reason why Cluthia is o n l y rarely recorded in Recent and fossil ostracod assemblages. Another reason for its rarity is due to its narrow en\ ironmen tnl tolerance. Cluthia is regarded ;IS ii cold water taxon, preferring boreal and Arctic waters. Its prcseiice in Late Tertiary and Quaternary sediments o f the Mediterranean and central part of thc eastern Atlantic ;ireas has been explained by periodic migrations from northern seas (Peypouquet, 1971;Ruggieri, 1977;Llano, 1981 ;Carbonnel & Balesio. 1982). I n the present paper, Cluthia miocenica sp. nov. is described from late Middle Miocene (Upper Badenian) deposits o f southern Poland (northerii periphery o f the Central Paratethys). This oldest known Occurrence supports my view point on t h e origin and migration o f Cluthia.
The described material is housed in the Institute o f Pa I eob i o l o g y , Pol ish Academy o f Sciences, Warsaw ( a b bre via ted Z P A L).

GEOGRAPHICAL DISTRIBUTION AND ENVIRONMENTAL TOLERANCE OF FOSSIL AND RECENT CLUTHIA
Thc Recent Cluthia includes two species which are ireprcscnted by rare individuals but which occur in many region., o f the Northern Hemisphere, in waters o f differen t depth and te mpcr;i t ure.
Norman ( 1 89 1 ) found Cluthia cluthae in the Bog Fjord ( E . Finnmark) at ;I depth o f 40-60111 while Scott ( 1 899; see Neale, 1973) collected it from FrnnL Joseph Land at ;I dcpth o f about 60 in. Hazel (1 970) also col-lected it from near Greenland at n depth of 1 3 m and determining its amphiatlantic bathymetry and distribution a s being between 2 0 and 3 0 0 m . Benson et al.
(1 983), however, investigating the biofacies of the Newfoundland continental slope recorded Cluthia cluthae from a depth o f 500 m t o over 1 500 m, from such different sediment substrates as silt, mud and sand.
C. cluthae has been described from the Bay o f Biscay from a depth ot 100 m and 600 m by Yassini (1 969), and Neale ( 1 975) described C. keiji from the eastern coast o f Spain from a depth of 81 m. Bonaduce et al. (1975) found this species in the Bay of Naples and the Adriatic Sea, where it occurs preferably at a depth of about 8 5 m o n a substrate varying from medium sand t o sandy silt. Neale (1 975) also mentioned the occurrence o f C. keiji near the Algerian coast.
In the Quaternary, C. cluthae is recorded from the N.E. Atlantic shelf of Morocco (Llano,198l), from the Bay of Biscay (Peypouquet, 1971) and from Malta (Neale, 1975). In the Pleistocene C. cluthae has been recorded from the N. W. coastal regions of the USSR (Neale, 1973), from S.W. Sweden (Lord, 1982) and from the Bay of Biscay (Moyes & Peypouquet, 1969). The oldest, so far, recorded occurrence of Cluthia (C. keiji) was described by Carbonnel & Ballesio (1982) from the Pliocene of south-east France and northern Italy.
According t o Hazel (1 970), the amphiatlantic temperature tolerance o f Recent species o f Cluthia is between 0°C (or even less) t o 7"C+ and that its southern range is limited by summer temperatures (see also Neale. 1973). Neale estimates that it is a summer surface water temperature o f 15°C that limits the southward distribution o f Recent and Pleistocene species o f Cluthia in the At I antic.
Other authors, (Moyes & Peypouquet. 1971 ;Carbonel, 1980;Llano, I981 ;Carbonnel & Ballesio, 1982) consider Cluthia not only t o be a cold water form but also nearshore in habit, and a s such is an indicator o f the palaeocoast in fossil forms. Peypouquet (1971) also considers the temperature tolerance of Recent Cluthia to be the factor limiting its geographical distribution. This author, investigating Recent and subfossil ostracod assemblages from the shelf sediments of the Bay of Biscay, included specimens of Cluthia into the palaeot ha n a t ocoe no sis which resulted from the b iocoe n 0 s is living during the last glaciation. Similarly Llano (198l), who analyscd Quaternary ostracod assemblages from the Moroccan coast, considered the specimens of Cluthia in his material to be representatives of northeastern Atlantic forms from the Norwegian Province, and to be indicative o f a cold water palaeothanatocoenosis. O n e may add here that Quaternary biocoenoses with Cluthia also contain other cold-water ostracod species. Carbonnel & Ballesio (1982), regarding Cluthia t o be a cold-water ostracod having a very short stratigraphical range in the Pliocene deposits in France and Italy, used it for correlation as well a s for designating a zone indicating Middle Pliocene cooling in the Mediterranean basin. In the light of these interpretations of the age and palaeotemperature conditions of Cluthia, one has doubts about the findings of Cluthia in the Recent Mediterranean Sea (Italy, Algeria, Spain and Yugoslavia coasts).

CLUTHZA MZOCENZCA SP. NOV. FROM THE MIDDLE MIOCENE OF S.E. POLAND
Cluthia miocenica sp. nov. has been found in the Middle Miocene (Upper Badenian) deposits of southeast Poland, in Roztocze region. Roztocze, which is a southern margin of the Lublin Upland, forms, together with other Polish Uplands, the northern margin of the Fore-Carpathian Depression. In the Miocene, Roztocze constituted a marginal part of the Central Paratethys and, therefore, deposits o f this age represent a shallow water. nearshore zone of sedimentation. The most common sediments are intercalating sands, marls and limestones.
A few specimens of Cluthia have been found in outcrops of Upper Badenian age in the northwest part of Roztocze at Weglin and Trzesiny. At Weglin (cf. Szczechura & Pisera, in press, fig. 2) it has been found in m a r k overlying lithothamnian limestones and in marly clay from the higher part of the section. In the marls, Cluthia miocenica is accompanied by relatively abundant Aurila cf. A . opaca,Aurila sp., and Semicytherura spp., and very rare Pterygocythereis jonesii, Bairdia sp., Kangarina abyssicola, Cytheropteron sp., Krithe sp., Pseudocythere cf. P . caudata, ?Argilloecia sp., Occultocythereis bituberculata and Cythereida acuminata . In the clays, Cluthia and Cythereidea acuminata only occur.
Diversity, taxonomic composition of ostracod assemblages accompanying Cluthia, density and population structure as well as analysis of the whole microfauna from Weglin (except from the topmost part of the section; cf. Szczechura & Pisera, in press) are indicative of a non-stable environment, with fluctuating bathymetry (deepening). A t least outer infralittoral (sensu Carbonel, 1980) conditions existed during sedimentation of the lower part of the section.
Sands contain a similar assemblage of ostracods although their frequency is lower than in the limestones and ostracods occur mostly as adult carapaces indicating a high rate of sedimentation.
Analysis of ostracod and forminifera distribution in the whole Trzesiny section suggests changing bathymetry and energy environment in a shallowing upward sequence.
Especially important seems to be the fact that although in all samples from Roztocze, Cluthia represents various environmental conditions regarding depth, character of substrate and hydrodynamic energy, it seems to represent rather uniform temperate temperature conditions. Differences existing between the Early and Late Badenian in the Central Paratethys, concern among others, microfauna distribution and are expressed by the disappearance of termophilic small planktonic and large benthic foraminifera in the Late Badenian. Based on this, I have designated (Szczechura, 1982(Szczechura, , 1984 Globigerinoides and Globigerina ecozones which represent respectively, a tropical climate in the Early Badenian and a temperate climate in the Late Badenian. In this biostratigraphical zonation, Cluthia belongs to the Globigerina ecozone. Of importance here seems to be the fact that deposits of the Globigerina ecozone are impoverished with regard to the numerous ostracod species present in deposits of the Globigerinoides ecozone (Szczechura & Pisera, in press).
According to earlier investigations, presented above. the occurrence of Cluthia in Poland probably records the drop in temperature of the shallow surface waters o f the Late Badenian of the Central Paratethys. The presence of Cluthia in deposits of the Middle Miocene of the Central Paratethys also hasother consequences in that it allows for the origin of Cluthia and the direction of migration to be different from that previously postulated.

ORIGIN AND MIGRATION PATHS OF CLUTHZA
Evaluating the so far known geographical and stratigraphical distribution of Cluthia (Fig. 1) there is no doubt that it appeared in the Middle Miocene (Late Badenian) of the Central Paratethys presumably during climate cooling. Later, in t h e Pliocene, it spread into the Tethys (France and Italy) and around its periphery. Northern seas were colonised by Cluthia only in the Quaternary, so they cannot be regarded a s provinces of origin of this genus.
The existence of ;i communication between the Paratethys and the Tethys in the Late Middle Miocene (Late Badenian) (Carbonnel & JiiiEck, 1977;JiiiEek, 1983) allowed Cluthia to migrate from the Paratethys into the Tethys and, as a consequence, into the eastern and northern Atlantic. At Roztocze, in deposits which are stratigraphical equivalents of those with Cluthia, both Carinocythereis carinata and Cyarnocytheridea dertonensis occur. These two species also occur in timeequivalent strata in Italy, and thus permit ;I correlatioh  (Carbonnel & JiiiEek, 1977;JiiiEek, 1983). The first of these two species lives today and has a wide disribution in the Mediterranean region and along the eastern coast of the Atlantic between lats. 25" and 60"N. Thus, it seems probable that the Paratethys, beginning in the Late Badenian, was the centre of origin of many marine ostracod species, known subsequently from the Late Miocene of the Tethys. So far, the influence of the Paratethys on the Tethys, based on os'tracods, was QoStUhted to exist in the latest Middle Miocene i.e. in the Sarmatian.
In the light of the data presented above, Cluthia from the bottom sediments of the Mediterranean Sea is an element of ii cool climatic paleothanatocoenosis or of a deep water (and so also cool-water) element of a Recent biocoenosis. However, to accept the living presence of Cluthia in thc present day Mediterranean Sea, one needs to find it with soft parts preserved. Description. Valve small. thin, laterally compressed, with lateral outline typical of genus. Maximum height anteriorly, greatest width posteroventrally. Both valves very similar in size and shape. Dorsal margin straight, ventral margin concave in middle part. Anterior margin broadly and somewhat obliquely rounded, posterior margin less broadly rounded. Anterior cardinal angle better developed than posterior one, being more distinct in the left valve. Distinct lateral inflation best marked behind and below muscle-scar field; in its lower part it extends up to the ventral margin. Weak rib-like inflation runs closely to the posterior margin, in its upper part disappearing below and before the hinge margin, whereas in its lower part gently passing into the ventral margin. Marginal part of the anterior end slightly removed outside and generally thickened distally. Valve surface regularly and densely pitted, with weak and tiny, irregular striae bordering posteriorly the lateral inflation.
Variation. Weak variation concerning the size, length: height ratio and details of the valves ornamentation have been observed.
Remarks. The described species is very close to Cluthia keiji Neale, 1975, described a s a Recent species from the Mediterranean region. In contrast to C. keiji, C. rniocenica is larger and lacks the posterodorsal, admarginal, riblike inflation.