New genera and species of cytheracean Ostracoda from the S.W. Atlantic

Five new genera of cytheracean Ostracoda are described from the S.W. Atlantic area. They are: Austrocytheridea and Papillosacythere, which belong to the Cytherideinae and Neocytherideinae respectively, and Austroaurila. Falklandia, and Meridionalicythere, which are all members of the Hemicytheridae.


INTRODUCTION
This paper forms part of a much larger study of the Recent Ostracoda of the Antarctic, sub-Antarctic, Falkland Islands and the coast and Continental Shelf of Tierra del Fuego, the Magellan Straits and the Argentinian, Uruguayan and southern Brazilian seaboard. The study is based on eulittoral and sublittoral samples collected by the senior author, assisted by Argentinian colleagues, during a number of excursions and expeditions made during [1970][1971][1972][1973]. A large number of sediment samples from the Continental Shelf and the estuary of the Rio de La Plata were made available by the Hydrographic Service of the Argentine Navy.
The Bairdiacea, marine Cypridacea and the cytherid family Pectocytheridae from this material formed the basis of a Magister thesis written by Moguilevsky (MS, 1976). The cytheracean family Leptocytheridae were studied by Whatley & Moguilevsky (1975). In 1984, the remainder of the material, together with additional samples provided by the British Antarctic Survey, was made the basis of three Magister theses at Aberystwyth. Coxill (MS, 1985) studied deep water and shelf faunas from the Antartic and South Scotia Sea and also those of the littoral and sublittoral of East Falkland. Toy (MS, 1985) studied the littoral faunas of Tierra del Fuego, both sides of the Magellan Straits and the Argentine Coast north to lat. 45"s. and sediment samples from the Continental Shelf north to the same latitude. Chadwick (MS, 1986) worked on the Ostracoda of the Argentine littoral from lat. 45"s. north to the estuary of the Rio de La Plata and from sediments from the Continental Shelf of northern Argentina, Uruguay and southern Brazil. He also studied a suite of samples from the estuary of the Rio de La Plata.
Details of the sampling localities and of the samples themselves can be found in the respective theses and these data will be published in a subsequent paper on the ecological and zoogeographical distribution of the Ostracoda of the region. These studies yielded a rich and diverse fauna of podocopid ostracods. For example, Moguilevsky recorded 16 species, Coxill 97 species, Toy 90 species and Chadwick 104 species.
All figured types of new species are housed in the collections of the Department of Zoology, British Museum (Natural History) and other figured specimens are house in the Micropalaeontology Museum, Department of Geology at Aberystwyth. A representative collection of all the species dealt with in this paper will be deposited in the Museo de la Plata, Argentina.
"v"-shaped vertically disposed frontal scar. Strongly dimorphic. Remarks. In its shape and outline, this genus resembles Ovocytheridea Grekoff, from the Cretaceous of Africa. The latter genus, however, differs in internal details, most importantly in its rather narrow avestibulate inner lamella. Some species of Cyamocytheridea Oertli are similar in shape but have a much less robustly developed median hinge element and a frontal scar which is more crescentic and which opens anteriorly rather than dorsally. Sarsicytheridea Athersuch, is similar internally but very different in shape. The genus is apparently monotypic and restricted to the southern S. W. Atlantic.      end, widest anteriorly. Approximately 25 simple (rarely bifurcating) radial pore canals anteriorly. Hinge strongly developed, antimerodont; terminal elements long. Adductor muscle scars well-spaced, frontal scar strongly "v"-shaped and vertically disposed.

Length Height
Holotype, 0 right valve (1986,507) (Coxill MS, 1985); in the eulittoral of Tierra del Fuego (Toy MS, 1985). Chadwick (Ms, 1986)  Remarks. This species is somewhat similar in shape to Falklandia ephippiata (Skogsberg) from the Falkland Islands, Tierra del Fuego and the littoral and shelf of southern Argentina. However, the dorsal margin of the latter is more horizontal and the anterolateral tubercular excrescence developed in both species in the female left valve, is not accompanied by a similar posteroventral excrescence in A. theeli as it is in F. ephippiata.
Brady's 1880 material of A. impluta included both that species and A. theeli. The lectotype selected for the former species by Puri & Hulings (1976, p. 278, pl. 9, figs. 15, 16) is fortunately clearly not A . theeli. A. impluta differs in lacking the anterolateral tubecle. Distribution. The type locality of this species is off the coast of the Province of Chubut, in 9m of water. Skogsberg (1928) also recorded it from off the coast of Tierra del Fuego. Kaesler et al. (1979) recorded it in the Magellan Straits and Coxill (MS, 1985) found it in littoral samples from East Falkland. Toy (MS. 1985) records it from the littoral of the Beagle Channel, the Magellan Straits, the north coast of Tierra del Fuego and along the littoral of the Argentine Coast to Bahia Solano, some 25km north of Comodoro Rivadavia, at about lat. 45'411's. Chadwick (MS. 1986) encountered the species in the Argentine littoral between Peninsula Valdez (lat. 42'47's.) and Mar del Plata (lat. 38"s.) and on the shelf between lilt. 36" 12's. and 42'23's. All the Continental Shelf specimens were dead but the species is commonly encountered live in littoral samples. particularly of algae. It does however, also occur live in littoral sediments, particularly those rich in organic detritus. Material. 2 juvenile valves. This species is notably larger than either A. impluta ro A . theefi the mean length of males for the three species being 0.95, 0.86 and 0.78mm respectively. It is most similar morphologically to A . theefi but differs from that species in its coarser ornament and in the rows of punctae which elaborate the alar rib. It also lacks the anterolateral tubercle in the female left valve which is such a diagnostic feature of A. theeli. Distribution. Skogsberg (1928) encountered this species on the Burwood Bank (lat. 53'45's.; long. 61'10'W.) at depths of 137-150m on mussel sand with stones. Hartmann (1962) found it at two littoral localities in the southern Chilean province of Magallanes. Kaesler et a f . (1979) record it from the Magellan Straits. In the present study, neither Toy nor Chadwick encountered the species but Coxill recovered two dead juveniles from a kelp (Macrocystis) holdfast in Stanley Harbour, Falkland Islands.

Remarks.
This as yet monotypic genus is apparently confined to the South Atlantic and southernmost South America. Falklandia somewhat resembles certain species of Austroaurila, particularly A. theeli (Skogsberg). The two genera, however can be readily distinguished on hingement, the latter being holamphidont and the former hemiamphidont. Although the female left valves of both F. ephippiata and A . theeli develop an anterolateral excrescence, that of the former is aligned vertically while that of the latter is either hemispherical or aligned horizontally and is almost smooth.
Falklandia ephippiata (Skogsberg), 1928 (PI. 2, figs. 8-14) 1920 Cythereis sp. Skogsberg: 145. 1928 Cythereis ( Creek, Port Louis, Falkland Islands. Coxill (MD, 1985) recovered 18 specimens in eulittoral and sublittoral algal samples from Stanley Harbour, Eliza Cove and the Estuary of the Murrel River, all in East Falkland, but failed to encounter the species in samples from Port Louis. Hartmann found it in the littoral of Tierra del Fuego. Toy (MS, 1985) recovered 250 specimens from littoral algal and sediment samples from the Beagle Channel, Magellan Straits and the Argentine coast north to Puerto Deseado (lat. 54'50's. to lat. 47'10' S.). The species was absent from shelf sediment samples and Chadwick failed to recover it in his study of the Argentine littoral Ostracoda north of lat.45"S.
Type species. Cythereis (Cythereis) discophora Skogsberg, 1928. Derivation of name. With reference to the apparent restriction of this genus to the South Atlantic. Diagnosis. A genus of the Hemicytheridae with large subrectangular to subtrapezoidal carapace; maximum height at the anterior cardinal angle. Dorsal margin, straight and inclined towards the posterior, or convex. Anterior margin well rounded; posterior subtruncate to bluntly pointed, apex below mid-height. Ornament reticulate and/or punctate, with or without costae. Dorsal loop and subalar ridge more or less well developed. Shell thick. Subcentral tubercle present but not prominent. Eye tubercle small, prominent. Inner lamella of median width with very narrow vestibulae at each margin. Hinge holamphidont, robustly developed. Posterior terminal element of right valve a boss-like tooth or a smooth arcuate bar. The two central adductor scars are subdivided. Strongly sexually dimorphic, males much more elongate than females. Remarks. This genus is based on the three specis M . discophora, M . mesodiscus and M . taeniata (all Skogsberg, 1928). Meridionalicythere differs from Aurila in shape, the nature of the adductor scars and in hingement. From Procythereis Skogsberg, it differs in both shape and ornament and in its much less strongly developed alar ridge. From Hernicythere it differs in being less subrectangular, in possessing a subcentral tubercle, a dorsal loop and an alar ridge. The genus is apparently confined to the S. W. Atlantic and southernmost South America.
Remarks. The mean length of this species (0.77nm) is slightly greater than that of M . mesodiscus (0.75 mm) and considerably greater than M . tueiniuia (0.69mm). M . discophora is the most strongly reticulate of the three species, its dorsal loop is more strongly developed than that of M . mesodiscus but slightly less than that of M . taeniata. Distribution. Skogsberg's original material was from Carenage Creek, Port Louis, Falkland Islands. Coxill (MS, 1985) recorded the species abundantly in littoral algae from around the Port Stanley area of East Falkland. Toy (MS, 1985) found more than 100 specimens from eulittoral algal and sediment samples from the Beagle Channel, the Magellan Straits and the Argentine coast north to Caleta Olivia, in the Province of Santa Cruz, at about lat. 46'30's. The species was absent from shelf sediment samples and Chadwick (MS, 1986) did not encounter it in his study of the Ostracoda north of lat. 45'.
Meridionalicythere mesodiscus (Skogsberg), 1928 (PI. 2, figs. 20, 21;PI. 3, figs. 1-9) 1928 Cythereis (Cythereis) mesodiscus Skogsberg: 87, pl. 2, figs. 2, 3;pl. 4, fig. 7, text-fig. 14. 1962 Aurila mesodiscus (Skogsberg), Hartmann: 237. 1979 "Aurila" mesodiscus (Skogsberg), Kaesler, Material. 399 adults and juveniles, many live. Remarks. This species differs from other members of the genus in the very elongate shape of the male and in the nature of its ornament. The posterodorsal loop is very weakly developed and the ornament comprises irregular reticulae posteriorly, subhorizontally aligned punctae within a reticulum in which the horizontal murae predominate medianly, and a weak irregular reticulum anteriorly, containing within the fossae a delicate secondary punctation. The subalar ridge is only weakly developed in this species. All these characters serve to distinguish this species from other members of the genus. Distribution. Very abundantly distributed throughout the area studied. Skogsberg (1928) first recorded it from a depth of 9 m off Puerto Madryn, Province of Chubut, at approximately lat. 42"50'S. and also from off Isla Nueva, south of the Beagle Channel. Hartmann (1962) recorded it from the littoral of Magallanes Province, southern Chile and Kaesler et al. from the Magellan Straits. Coxill (MS, 1985) found 29 specimens from eulittoral and upper sublittoral environments around the Port Stanley area of East Falkland. Toy (MS, 1985) records the species in algal samples and sediments of various types from the littoral of the Beagle Channel, the northern coast of Tierra del Fuego, the Magellan Straits and the Argentine coast north to Caleta Olivia, near the boundary between the provinces of Santa Cruz and Chubut, at about lat. 45'40's. Chadwick (NS, 1986)  The senior author also wishes to thank the Hydrographic Service of the Argentine Navy for allowing him access to a large number of sediment samples from the Continental Shelf. Thanks are particularly due to Capitan de Fregata Lara for his help and interest in the project.
The British Antarctic Survey and the Governor of the Falkland Islands are thanked for all their assistance during the collecting expedition to East Falkland.
Thanks are also due to Sr. Jorge Mennuchi for all his assistance in the laboratory preparation of the samples in the Department of Micropalaeontology , University of La Plata. John Chadwick wishes to acknowledge a N. E. R. C. Studentship, held during his Magister studies. Caroline Maybury has critically read the MS and helped in many other ways. Our sincere thanks to her and to everyone associated with the project.
All from eulittoral algae, north shore of Beagle Channel, just west of Ushuaia, lat. 54'50's.       All from algae in ria, immediately south of San Antonio Oeste, Rio Negro Province, Argentina, lat. 4W40'S.