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Ameghiniana

versión impresa ISSN 0002-7014

Ameghiniana vol.46 no.2 Buenos Aires abr./jun. 2009

 

ARTÍCULOS ORIGINALES

The Family Thaerocytheridae Hazel, 1967 (Ostracoda) from the Southern Brazilian Continental Shelf

Maria Inês Feijó Ramos1, João Carlos Coimbra2 and Robin Whatley3

1Museu Paraense Emílio Goeldi, CCTE, Campos de Pesquisa, Av. Perimetral, 1901,Cx. P. 399, CEP. 66077-530, Belém, PA, Brasil. mramos@museu-goeldi.br
2Departamento de Paleontologia e Estratigrafia, Universidade Federal do Rio Grande do Sul, Cx.P. 15001, CEP. 91501-970, Porto Alegre, RS, Brasil. joao.coimbra@ufrgs.br
3Micropalaeontology Unit, Department of Geology, University of Wales, Aberystwyth, SY23 3DB, UK. riw@aber.ac.uk

Abstract. Of a total fauna of 95 species of benthic Ostracoda recovered from dry sediments from the southern Brazilian continental shelf, 8% belong to the Family Thaerocytheridae. Six species assigned to this family are discussed and figured in this paper; four of these, Bradleya pseudonormani, B. kaesleri, Muellerina cribrosa and Quadracythere nealei are described as new, while Brasilicythere reticulispinosa and Quadracythere eichlerae were described for the first time from the Quaternary of Pelotas Basin, in southern Brazil. Most of these species are restricted to the southern part of the Southwest Atlantic Ocean, and their geographical distribution ranges from the southern Brazilian continental shelf, in Rio de Janeiro State (21ºS), to the Argentinian continental shelf (52ºS). Three species are restricted to the southern Brazilian continental shelf: B. kaesleri, M. cribrosa. and Q. nealei, while three other species have fossil records: B. reticulispinosa (Oligocene to Recent), Q. eichlerae and B. kaesleri (both Holocene to Recent).

Resumen. La Familia Thaerocytheridae Hazel, 1967 (Ostracoda) de la plataforma continental del sur de Brasil. De las 95 especies de ostrácodos bentónicos recuperadas en muestras secas de sedimentos provenientes de la parte sur de la plataforma continental brasileña, 8% pertenecen a la Familia Thaerocytheridae. De éstas Bradleya pseudonormani, B. kaesleri, Muellerina cribrosa y Quadracythere nealei se describen e ilustran por primera vez. Brasilicythere reticulispinosa y Quadracythere eichlerae fueron descriptas para el Cuaternario de la Cuenca de Pelotas, en el sur de Brasil. La distribución geográfica de la mayoría de las especies comprende desde la Plataforma Sur Brasileña, en el Estado de Río de Janeiro (21ºS) hasta la Plataforma Continental Argentina (52ºS). Bradleya kaesleri, M. cribrosa y Q. nealei están restringidas a la parte sur de la Plataforma Continental Brasileña. Tres especies tienen registro fósil: B. reticulispinosa (Oligoceno a Reciente), Q. eichlerae y B. kaesleri (ambas, Holoceno a Reciente).

Key words. Ostracoda; Thaerocytheridae; Recent; Brazilian Continental Shelf.

Palabras clave. Ostrácodos; Thaerocytheridae; Reciente; Plataforma Continental Brasileña.

Introduction

The study of benthic Recent marine Ostracoda from the southern Brazilian continental shelf of the sub-orders Podocopina, Platycopina and Clado-copina allowed the identification of 95 species, 29 of which were new, 13 were left in open nomenclature and 53 were previously described (Ramos, 1998). No less than 62% species are restricted to the southern Brazilian continental shelf while 38% of species extend southwards to the Argentinean coasts. This is largely due to the uniformity of the water mass, with a subtropical climate extended southward by the Brazil Counter Current. Part of this endemism began in the immediate post-Miocene when the present continental plate and oceanic configurations were established. Among the 95 species identified, approximately, one third had their origin in the Neogene or Quaternary of South America; only three species have their first appearance in the Oligocene.
The families Pontocyprididae and Bairdiidae were published in Ramos et al. (2004), where previous studies on Recent and Sub-Recent marine benthic ostracods in this part of the Southwest Atlantic Ocean are summarized.
The study area comprises the southern Brazilian continental shelf, from Rio de Janeiro (Lat. 21ºS-Long. 40ºW) to Rio Grande do Sul states (Lat. 35ºS-Long. 54ºW), extending almost 2050 km in length (figure 1). According to Chaves (1983), this large area is known as South Region and reaches from 100 to 160 m in water depth, while its maximum width is around the city of Santos (São Paulo State), at 230 km, the minimum being off the town of Cabo Frio (Rio de Janeiro State), at only 80 km (figure 1). The area is strongly affected by the subantarctic waters brought northward by the Malvinas (Falklands) Current. The influence of this current on the Brazilian shelf is felt as far north as ~23ºS, near the town of Cabo Frio.


Figure 1. Map of the study area showing bathymetry (modified from Kowsmann and Costa, 1979) / mapa de ubicación del área estudiada mostrando la batimetría (modificado de Kowsmann y Costa, 1979).

Material and methods

This study is based on 500 samples collected both by Phillips and van Veen grabs during a series of cruises throughout the southern Brazilian continental shelf. The REMAC Project was coordinated by Petróleo Brasileiro S.A.-PETROBRAS (legs 1, 2, and 3); the Geomar VI, coordinated by the hydrographic service of the Brazilian Navy (DHN); and the Research Vessel "El Austral". The material was provided as dried sediment. The preparation of the samples was by standard methods. Only 207 samples yielded ostracods. The specimens were illustrated by the first author using "Cambridge Stereoscan 120" SEM from the Department of Geology, University of Wales, Aberystwtyh, UK. The type material is housed in the collections of the 'Museu de Paleontologia', Universidade Federal do Rio Grande do Sul, Section of Ostracoda, under catalogue numbers MP-O-1916 to MP-O-1937.

Abbreviations: H, height; L, length; W, width; RV, right valve; LV, left valve; MP-O, Ostracoda collection of Universidade Federal do Rio Grande do Sul, Brazil. All dimensions are in mm.

Systematic paleontology

Class Ostracoda Lattreille, 1806
Order Podocopida Müller, 1894
Suborder Podocopina Müller, 1894
Superfamily Cypridacea Baird, 1845
Family Thaerocytheridae Hazel, 1967
Subfamily Bradleyinae Benson, 1972

Genus Bradleya Hornibrook, 1952

Type-species. Cythere arata Brady, 1880.

Bradleya pseudonormani sp. nov. Figures 2.1-6


Figure 2. 1-6, Bradleya pseudonormani; 1, MP-O-1916 (holotype), female, carapace, LV, external view / holotipo, hembra, carapazón, VI, vista externa, 48,78X; 2, MP-O-1917 (paratype), female, carapace, dorsal view / paratipo, hembra, carapazón, vista dorsal, 50X; 3, Holotype, female, carapace, RV, external view / holotipo, hembra, carapazón, VD, vista externa, 50X; 4, Holotype, female, LV, internal view / holotipo, hembra, carapazón, VI, vista interna, 50X; 5, Holotype, female, carapace, RV, internal view / holotipo, hembra, carapazón, VD, vista interna, 50X; 6, MP-O-1918 (paratype), male, carapace, dorsal view / paratipo, macho, carapazón, vista dorsal, 50X; 7-12, Bradleya kaesleri; 7, MPO-1922 (holotype), female, carapace, LV, external view / holotipo, hembra, carapazón, VI, vista externa, 57.14X; 8, MP-O-1926 (paratype), male, carapace, dorsal view / paratipo, macho, carapazón, vista dorsal, 55X; 9, Holotype, female, carapace, RV, external view / holotipo, hembra, carapazón, VD, vista externa, 54.05X; 10, Holotype, female, carapace, LV, internal view / holotipo, hembra, carapazón, VI, vista interna, 57,14X; 11, Holotype, female, carapace, RV, internal view / holotipo, hembra, carapazón, VD, vista interna, 54.05X; 12, MP-O-1923 (paratype), female, carapace, dorsal view / paratipo, hembra, carapazón, vista dorsal, 50X ; 13-16, Brasilicythere reticulispinosa; 13, MP-O-1927, female, carapace, LV, external view / espécimen ilustrado, hembra, carapazón, VI, vista externa, 57.14X; 14, MP-O-1927, female, carapace, dorsal view / hembra, carapazón, vista dorsal, 57.14X; 15, Female, carapace, RV, external view / hembra, carapazón, VD, vista externa, 55,5X; 16, MP-O-1928, male, carapace, dorsal view / macho, carapazón, vista dorsal, 52.63X.

1998a. Bradleya normani (Brady, 1866); Whatley, Moguilevsky, Chadwick, Toy and Ramos, p. 108, pl. 5, fig. 1-2.
1866. [ non] Cythere normani Brady, p. 379, pl.61, fig.5a-d.
1880. [ non] Cythere normani Brady, 1866; Brady, p. 101, pl. 17, fig. 3a-d.
1972. [ non] Bradleya normani (Brady, 1866); Benson, p. 38, fig. 13c, pl. 2, fig. 7, pl. 7, fig. 8, pl. 8, fig. 6.
1996. [ non] Bradleya normani (Brady, 1866); Whatley, Staunton, Kaesler and Moguilevsky, p. 3, fig. 12, 13.
2003. Bradleya sp. Drozinski, Coimbra, Carreño and Bergue, p. 68, fig. 8: B, C.
2005. Bradleya sp. Machado, Coimbra and Carreño, p. 243, pl. 3, fig. 16.

Derivatio nominis. Named because it is morphologically similar to yet subtly different from B. normani (Brady).

Type material. MP-O-1916 (holotype), female, carapace, south Brazilian continental shelf, sample GVI-370, lat. 30º37´S; long. 49º06´W, depth 148 meters, silt and sand biodetritical sediments, Recent; MP-O-1917 (paratype), female, carapace; MP-O-1918 (paratype), male, carapace; MP-O-1919 (paratype), VE, female; MP-O-1920 (paratype), VE, female; MP-O-1921 (paratype), VE, male.
Material. 1552 adult valves and 6486 juveniles.

Diagnosis. Carapace subquadrate to subrectangular in lateral view, thick-shelled; strongly reticulated; prominent and arcuate dorsal rib, running from antero-median region to the posterior cardinal angle; ventral rib well developed with a terminal spine. Dorsal margin irregular and discontinuous with two depression separated by a short spine. The antero-marginal rib denticulate in the ventro-median region and separated of the ocular rib by four or five large fossae; the submarginal rib strongly marked for the genus.
Description. Carapace subquadrate to subrectangular, thick-shelled. Maximum height in the postero
median region. Dorsal margin almost right, irregular and discontinuous with two depression separated by a short spine and slightly concave in the posterior region; tubercle ocular prominent. Ventral margin convex but with a small oral incurvature in internal view. Anterior margin obliquely rounded and finely denticulate in the ventro-median region. Posterior margin slightly produced and denticulate in the ventro-median portion, more developed in the right valve. Surface coarsely reticulate with large fossae and thick muri. Prominent and arcuate dorsal rib, running from the antero-median region to the postero cardinal angle. The antero-marginal rib separated from the ocular rib by four or five large fossae; the submarginal one strongly marked for the genus. Ventral rib well developed with a terminal spine, frequently broken. In dorsal view, males more subhastate than females. Internal features typical of the genus. Sexual dimorphism conspicuous; males more elongate and narrower than females.
Dimensions. MP-O-1916, female, carapace, RV, L: 0.80; H: 0.46; LV, L: 0.82; H: 0.52; W: 0.54. Paratype MP-O-1917, female, carapace; RV, L: 0.80; H: 0.52; LV, L: 0.80; H: 0.50; W: 0.54. Paratype MP-O-1918, male, carapace, RV, L; 0.80; H: 0.46; LV, L: 0.80; H: 0.44; W: 0.50. Paratype MP-O-1919, LV, female; L: 0.80; H: 0.50. Paratype MP-O-1920, LV, female; L: 0.80; H: 0.50. Paratype MP-O-1921, LV, male; L: 0.72; H: 0.44. All specimens are adult.
Remarks. Most Bradleya species have very similar reticulation patterns, i.e. B. dictyon (Brady, 1880) and B. normani (Brady, 1866) and are somewhat difficult to distinguish, as discussed by Benson (1972). Bradleya pseudonormani sp. nov. and B. normani have very similar ornamentation, although B. pseudonormani sp. nov. differs from B. normani in being more robust, and its submarginal anterior rib is not continuous. In B. pseudonormani, this rib extends from the eye tubercle to the antero-median region, almost disappearing and splitting from the ventral submarginal rib; B. pseudonormani is smaller and more arcuate dorsally, with a well developed dorsal rib extending from the antero-median region to the postero-dorsal cardinal angle. B. reighantzi Sanguinetti, 1979 and B. pelotensis Sanguinetti et al., 1991 described from the Quaternary of the Pelotas Basin, southernmost Brazil are also very similar to B. pseudonormani sp. nov. differing only in a few details of the reticulation pattern, more concave dorsal region and thicker muri. Although the specimens of B. pelotensis are poorly preserved, this species is more similar to B. rheigantzi than to B. pseudonormani sp. nov. differing from the latter in its more delicate ribs and few details of the ornamentation pattern. Probably B. pelotensis and B. rheigantzi are the same species.

Distribution. In the present study B. pseudonormani sp. nov. occurs between 22º24.5' and 33º51' S, from 8 to 156 m depth, predominantly on silt sediments. In previous studies, this species was registered from Recent sediments from Argentinean, Uruguayan and Brazilian continental shelves (Whatley et al., 1998a) from 30º54' S to 41º52.2'S. Additional register to the Brazilian sediments can be found in Drozinski et al. (2003) who found autochthonous specimens between 100 and 505 m along coast of the Rio Grande do Sul, while Machado et al. (2005) registered it on Cabo Frio coast between 21 and 75 m.

Bradleya kaesleri sp. nov. Figure 2, 7-12

1977. Bradleya sp. Vicalvi, Kotzian and Forti-Esteves, p. 95, pl. 5, fig. 3.

Derivatio nominis. Named in honour of the late Professor Roger LeRoy Kaesler, a particular friend of RCW, in recognition of his enormous contribution to ostracod studies, with special reference to the mathematical/statistical approach and to his editorship of the 'Treatise on Invertebrate Paleontology' series.

Type material. MP-O-1922 (holotype), female, carapace, South Brazilian continental shelf, sample GVI-349, lat. 31º24'S, long. 50º41'W, 60 m depth and silt-sandy with biodetritus sediments, Recent; MP-O-1923 (paratype), female, carapace; MP-O-1924 (paratype), male, carapace; MP-O-1925 (paratype), female, carapace; MP-O-1926 (paratype), male, carapace.
Material. 109 adults and 313 juveniles.

Diagnosis. Carapace sub-rectangular. Large anterior rib, separated from the delicate and short ocular rib by three or four large fossae. Prominent dorsal rib, gently arcuate extending to the antero-median region, above the ocular tubercle. Ventral rib thick and with six or seven large adjacent fossae.
Description. Carapace sub-rectangular, thick-shelled. Greatest height 1/3 of the distant from the anterior margin. Dorsal margin almost straight, slightly prominent region of in the eye tubercle. Ventral margin slightly sinuous, with gently oral incurvature. Anterior margin obliquely rounded and finely denticulate throughout; posterior margin slightly produced below mid-height with some five small spines exposed discordantly and frequently broken. Surface strongly ornamented by a rough and well defined reticulum. Dorsal rib conspicuous, gently arcuate, extending from the antero-median to postero-dorsal region. Anterior marginal rib large. A very weak ocular rib is separated from the marginal rib by three or four large fossae. Ventral rib thick, with 6-7 large adjacent fossae and a very small terminal spine. Subhastate in dorsal view. Internal features as for genus. Sexual dimorphism
evident; males more elongate and narrower than females.
Dimensions. Holotype MP-O-1922, female, RV, L: 0.74; H: 0.40; LV, L: 0.70; H: 0.40; W: 0.46. Paratype MP-O-1923, female, RV, L: 0.76; H: 0.42; LV, L: 0.74; H: 0.42; W: 0.46. Paratype MP-O-1924, male, carapace, RV, L: 0.70; H: 0.36; LV, L: 0.74; H: 0.42; W: 0.40. Paratype MP-O-1925, female, juvenile, carapace, RV, L: 0.66; H: 0.30; LV, L: 0.66; H: 0.30; W: 0.40. Paratype MP-O-1926, male, carapace, RV, L: 0.70; H: 0.34; LV, L: 0.70; H: 0.34; W: 0.40.
Remarks. Bradleya kaesleri sp. nov. is very similar to Bradleya sp. Coimbra et al. (1999), from the Equatorial Brazilian continental shelf, but differs in its wider antero-marginal rib, smaller number of antero-marginal fossae, weaker ocular rib, and in the details of the antero-median reticulation. Bradleya kaesleri sp. nov. is also similar to Bradleya pseudonormani, differing mainly in possessing a more rectangular outline, small size and a rougher reticulate ornamentation, and a weaker and shorter ocular rib.
Distribution.
In the present study B. kaesleri sp. nov. occurs between latitudes 22°24.5' and 32°57'S, from 34 to 155 m depth, predominately on silty sediments. Vicalvi et al. (1977) registered fossil specimens of this species in a Holocene core from in the continental shelf of São Paulo State, Brazil.

Subfamiy Thaerocytherinae Hazel, 1967

Genus Brasilicythere Sanguinetti, Ornellas and Coimbra, 1991

Type species. Brasilicythere reticulispinosa Sanguinetti, Ornellas and Coimbra, 1991.

Brasilicythere reticulispinosa Sanguinetti, Ornellas and Coimbra, 1991 Figures 2.13-16

1977. Australicythere sp. 4. Valicenti, p. 94, pl. 1, fig. 6.
1977. Australicythere sp. Vicalvi, Kotzian and Forti-Esteves, p. 3, fig. 6.
1991. Brasilicythere reticulispinosa gen. et sp. nov. Sanguinetti, Ornellas and Coimbra, pl. 2, fig. 6-16.
1997. Brasilicythere  reticulispinosa  Sanguinetti,  Ornellas  and Coimbra, 1991; Whatley, et al., p. 39, pl. 6, fig. 4.
1998a. Brasilicythere reticulispinosa Sanguinetti, Ornellas and Coimbra, 1991; Whatley et al., p. 102-103, pl. 3, fig. 14-15.
1999.  Brasilicythere   reticulispinosa   Sanguinetti,Ornellas   and Coimbra, 1991; Carreño et al.:, p. 37, pl. 1: 12.
2003.  Brasilicythere  reticulispinosa  Sanguinetti,  Ornellas  and Coimbra, 1991; Drozinski et al., p. 68, fig. 8: A
2005.  Brasilicythere  reticulispinosa  Sanguinetti,  Ornellas  and Coimbra, 1991; Machado et. al., p. 243, pl. III, fig. 17.

Material. 958 valves, 87 carapaces and 2954 juveniles.

Dimensions. MP-O-1927 (homotype), female, carapace, RV, L: 0.72; H: 0.44; LV, L: 0.70; H: 0.44; MP-O-1928 (homotype), male, carapace, RV, L: 0.76; H: 0.42; LV, L: 0.76; H: 0.42; W: 0.38.
Remarks. The specimens recovered from the studied samples are very similar to the holotype described from the Post-Miocene of the Pelotas Basin, south-ernmost Brazil by Sanguinetti et al. (1991), differing only in the more developed and better preserved ornamentation. Brasilicythere reticulispinosa is similar to Brasilicythere bensoni Sanguinetti, 1979 from the Miocene of the Pelotas Basin, but has more evident reticulation and antero-median ribs, and less promi-nent cardinal angles, eye and subcentral tubercle.
Distribution. In the present study this species occurs between 22º42.5' and 34º29.5'S, from 22 to 158 m depth, mainly in silt. This species has been recorded previously from Recent sediments in Brazil and Argentina between 24º42.5' and 52º15.8'S, from the littoral to 160 m of depth, in coarse sand to silt (Whatley et al., 1997, 1998a). Drozinsky et al. (2003) found this species in a sample at 160 m from the Rio Grande do Sul coast, and, finally, Machado et al. (2005) found it in Recent sediments from Cabo Frio, at 58 and 66 m, in fine and very fine sand. It occurs in the Quaternary of the Pelotas Basin and in the Holocene of the São Paulo continental shelf. The oldest record is from the Oligocene of the Monte León Formation, Argentina (Valicenti, 1977).

Genus Muellerina Bassiouni,1965

Type-species. Cythere latimarginata Speyer, 1863.

Muellerina cribrosa sp. nov. Figures 3.1- 6


Figure 3. 1-6, Muellerina cribosa sp. nov., 1, MP-O-1929 (holotype), female, carapace, LV, external view / holotipo, hembra, carapazón, VI, vista externa, 60.6X; 2, MP-O-1930 (paratypes), female, carapace, dorsal view / paratipo, hembra, carapazón, vista dorsal, 60.6X; 3, Holotype, female, carapace, RV, external view / holotipo, hembra, carapazón, VD, vista externa, 60.6X; 4, Holotype, female, carapace, LV, internal view / holotipo, hembra, carapazón, VI, vista interna, 60.6X; 5, Holotype, female, carapace, RV, internal view / holotipo, hembra, carapazón, VD, vista interna, 60.6X; 6, MP-O-1931 (paratypes), carapace, male, dorsal view / paratipo, macho, carapazón, vista dorsal, 60.6X; 7-8, Quadracythere eichlerae Carreño et al., 1997; 7, MP-O-1933, female, carapace, LV, external view / hembra, carapazón, VI, vista externa, 58.8X; 8, Female, carapace, RV, external view, hembra, carapazón,VD,vista externa, 57.1X; 9-14, Quadracythere nealei sp. nov., 9, MP-O-1935 (holotype), female, carapace, RV, internal view / holotipo, hembra, carapazón, VD, vista interna, 52,4X; 10, Holotype, female, carapace, LV, external view / holotipo, hembra, carapazón, VI, vista externa, 52.4X; 11, Holotype, female, carapace, RV, external view / holotipo, hembra, carapazón, VD, vista externa, 52.4X; 12, Holotype, female, carapace, dorsal view / holotipo, hembra, carapazón, vista dorsal, 52.4X; 13, Holotype, male, carapace, LV, external view / holotipo, macho, carapazón, VI, vista externa, 50X; 14, Holotype, male, carapace, RV, external view / holotipo, macho, carapazón, VD, vista externa, 50X.

1997. Muellerina sp. Whatley, Moguilevsky, Toy, Chadwick and Ramos, p. 71, pl. 11, figs. 5, 6.
2005. Muellerina sp. Machado, Coimbra and Carreño, p. 243, pl. 3, fig.18.

Derivatio nominis. L. Because of the slit-like fossae of its ornamentation.

Type material. MP-O-1929 (holotype), female, carapace, South Brazilian continental shelf, sample Leg 3-3297 (22º21.5'S-40º59.9'W, 49 m); MP-O-1930 (paratypes), female, carapace; MP-O-1931 (paratypes), male, carapace; MP-O-1932 (paratypes), RV, female.

Diagnosis. Medium, thick-shelled. Marginal rim very strong. Irregularly reticulate with wide muri, deep cribrose fossae. Large, smooth subcentral tubercle.

Material. 77 adults and 8 juveniles.

Description. Medium sized. Thick-shelled, elongate and subrectangular in lateral view. Greatest height at anterior cardinal angle. LV with straighter dorsal margin than RV, with conspicuous cardinal angles mainly posteriorly. Ventral margin with slight, but well defined oral incurvature. Anterior margin broadly but obliquely rounded, finely denticulate. Posterior margin with a truncate and buntly denticulate caudal process. Surface irregularly reticulate with wide muri, deep cribrose fossae. Prominent subcentral tubercle with smooth surface. Large marginal rib extending around the free margin; strongest anteriorly and posteriorly, proximally limited by the adjacent deep marginal sulcus. In dorsal view, elongate with greatest width at subcentral tubercle. Internal features with holamphidont hinge, anterior tooth small, posteriorly stepped. The other features as for genus. Sexual dimorphism few developed; males less inflated than females.
Dimensions. MP-O-1929 (holotype), female, carapace, RV, L: 0.66; H: 0.30; LV, L: 0.66; H: 0.30; MP-O-1930 (paratype), female, carapace, RV, L: 0.66; H: 0.30; MP-O-1931 (paratype), male, carapace, RV, L:
0.66; H: 0.30; LV, L: 0.68; H: 0.32; MP-O-1932 (paratype) female, RV, L: 0.70; H: 0.32. All specimens are adult.
Remarks. This species differs considerably from Muellerina latimarginata (Speyer, 1863) from the Tertiary of Belgium in having a stronger marginal rib, smooth subcentral tubercle surface, deeper submarginal furrow, and anterior denticulate margin.
Distribution. On the Brazilian continental shelf this species occurs between 22º21.5' and 34º26.5'S and 22 to 153 m depth, mainly on sandy sediments. In the littoral of Argentina and in the estuary of the Rio de la Plata, between lat. 36º and 38ºS, in muddy-silt sediments.

Genus Quadracythere Hornibrook,1952

Type-species. Cythere truncula Brady, 1898.

Quadracythere eichlerae Carreño, Coimbra and Sanguinetti, 1997 Figures 3.7-8

1975. Quadracythere n. sp. Bertels, p. 350, pl. 5, fig. 9.
1991. Quadracythere sp. Sanguinetti, Ornellas and Coimbra, p. 151, pl. 5, fig. 11,16.
1997. Quadracythere sp. Whatley, Toy, Chadwick and Ramos, p. 71, pl. 6, fig. 14.
1997. Quadracythere eichlerae Carreño, Coimbra and Sanguinetti, p. 36, fig. 2: 17-19, 27, 28.
1998a. Quadracythere amplioreticulata Whatley, Moguilevsky, Chadwick, Toy and Ramos, p. 108, pl. 5, fig. 3-6.
1999. Quadracythere eichlerae Carreño, Coimbra and Sanguinetti, 1997; Carreño et al, p. 122, pl. 1, fig. 17. [ non] 
2003. Quadracythere  eichlerae  Carreño,  Coimbra  and Sanguinetti, 1997; Drozinski et al., p. 68, fig. 8D. [ non] 
2005. Quadracythere  eichlerae  Carreño,  Coimbra  and Sanguinetti, 1997; Machado et al., pl. 4, fig. 2.

Material. 73 valves, 5 carapaces and 88 juvenils.

Dimensions. MP-O-1933 (homotype), carapace, female, RV, L: 0.70; H: 0.42; LV, L: 0.68; H: 0.42; MP-O-1934 (homotype), carapace, male, RV, L: 0.68; H: 0.38; LV, L: 0.68; H: 0.36. All specimens are adult.
Remarks. The present species is similar to Quadra
cythere nealei sp. nov. described herein. However, in Q. eichlerae the dorsal rib is much less well-developed, the antero and postero-marginal denticulation is more delicate or absent, the subcentral-tubercle is well defined and pitted, and the overall size less.
Distribution. In the present study this species occurs between 23º50' and 34º51'S, from 4 to 156 m depth, mainly from fine sand. It also occurs in Recent sediments along the Argentinean coast, from the littoral to 100 m depth, between 38ºS and 51º38´S (Whatley et al., 1997, 1998a). This species occurs fossil in the Quaternary of the Pelotas Basin, southernmost Brazil (Sanguinetti et al., 1991 and Carreño et al., 1997, 1999) and the Pleistocene of Argentina (Bertels, 1975).

Quadracythere nealei sp. nov. Figures 3.9-14

2003. Quadracythere eichlerae Carreño, Coimbra and Sanguinetti,
1997; Drozinski et al., p. 68, fig. 8D. 2005. Quadracythere eichlerae Carreño, Coimbra and Sanguinetti,
1997; Machado et al., p. 4, fig. 2. 1997.  [ nonQuadracythere  eichlerae  Carreño,   Coimbra   and Sanguinetti, p. 36-38, fig. 2: 17-19, 27-28.

Derivatio nominis. In honour of the late Professor John William Neale in recognition of his very significant contribution to the study of Ostracoda.

Type material. MP-O-1935 (holotype), female, carapace, South Brazilian continental shelf, sample Geomar VI-362 (31º06'S-49º46'W, 135 m); MP-O-1936 (paratype), male, carapace; MP-O-1937 (paratype), RV, male.

Diagnosis. Large. Subquadrate to subrectangular in lateral view. Posterior margin with a short caudal process medianly; stout, blunt denticles in the ventral half. Ornament reticulate with large, some-what deep fossae. Subcentral tubercle nearly defined. Ventrolateral rib subalate; terminal spine small.

Material. 34 valves and 425 juvenils.

Description. Carapace large, thick-shelled, sub-quadrate to subrectangular in lateral view. Maximum height between cardinal angles. Dorsal margin straight, obscured by dorsal rib in the posterior half. Ventral margin slightly convex with oral concavity more pronounced in RV. Anterior margin broadly, but slightly obliquely rounded in ventral direction, denticulate. Posterior margin with a short caudal process medianly; stout, blunt denticles in the ventral half. Ornament reticulate with large, somewhat deep fossae. Antero-marginal rib delicate. Ventro-lateral rib gentle, subalate, and with a very small terminal spine. Dorsal rib overreaches the posterior half of the dorsal margin. Subcentral tubercle poorly defined. Eye tubercle prominent. In dorsal view subeliptical with maximum width at subcentral tubercle. Internal features as for genus. Sexual dimorphism present; males smaller and narrower than females.
Dimensions. MP-O-1935 (holotype), carapace, female, RV, L: 0.82; H: 0.50; MP-O-1936 (paratype), carapace, male, RV, L: 0.80; H: 0.48; LV, L: 0.80; H: 0.48; MP-O-1937 (paratype), male, RV, L: 0.80; H: 0.48. All specimens are adult.
Remarks. Q. nealei sp. nov. is similar to Cythereis (Procythereis) iganderssoni Skogsberg, 1928, from Tierra del Fuego. However, that species is somewhat larger, with weaker reticulation and conspicuous differences in the dorsal rib and internal features. See also remarks of Q. eichlerae.
Distribution. In the present study this species occurs between 22º21.5' and 34º26.5'S, from 23 to 164 m depth, predominantly on sandy sediments. Drozinsky et al. (2003) registered authoctonous specimens of Quadracythere nealei at 160 m from Recent sediments of the Rio Grande do Sul continental shelf while Machado et al. (2005) found the same species in the Cabo Frio coast, between 20 and 75 m.

Conclusions

The study of Recent marine benthic ostracods of the family Thaerocytheridae from the southern Brazilian continental shelf resulted in the description of four new species: Bradleya pseudonormani, B. kaesleri, Muellerina cribrosa and Quadracythere nealei, and in the record of Brasilicythere reticulispinosa Sanguinetti et al., 1991 and Quadracythere eichlerae Carreño et al, 1997. Most of these species are restricted to the southern part of the Southwest Atlantic Ocean, and their geographical distribution ranges from the south Brazilian continental shelf, Rio de Janeiro State (21ºS) to the Argentinian continental shelf (52ºS). Only two species are restricted to the southern Brazilian continental shelf: Quadracythere nealei. and B. kaesleri. The first species ranges from 22º21.5' to 34º26.5'S, and the second from 22°24.5 to 32°57'S, respectively. Muellerina cribrosa also reaches the Uruguayan coast, in the estuary of the River Plate at 38°S (Whatley et al., 1998a) but its was probably transported because on-ly few valves and juveniles were found at this locality. In the present study this species occurs between 22º21.5'S and 34º26.5'S, and seems at the present day to be restricted to the southern Brazilian continental shelf.
Three species have fossil records: Brasilicythere reticulispinosa Sanguinetti, 1979 from the Oligocene of
Argentina, the Pleistocene of Pelotas Basin and the Holocene of São Paulo State coast; Quadracythere eichlerae Carreño et al., 1997 from the Pleistocene of Argentina and Pelotas Basin (Brazil) and, finally, Bradleya kaesleri from the Holocene of São Paulo State coast.

Acknowledgements

The authors are grateful to CECO (Centro de Estudos Costeiros e Oceanográficos) at Universidade Federal do Rio Grande do Sul for provision of samples; the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil) by the financial support (grants 520309/99-5, 475313/03-8, 473971/2006-2 and 305537/2006-7). RCW thanks the Royal Society for funds that allowed him to undertake a number of visits to Brasil and Argentina in association with this and other studies of marine Ostracoda. We thank A.L. Carreño (Universidade Nacional Autónoma do México) for help with Spanish translations.

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Recibido: 9 de mayo de 2008.
Aceptado:
15 de diciembre de 2008.