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Desotodinium wrennii
Desotodinium wrennii De Schepper et al., 2004, p.633, fig.7, nos.1–16.
Holotype: De Schepper et al., fig.7, nos.1–6.
Age: Pliocene.
Original description (De Schepper):
DESOTODINIUM WRENNII new species Figure 7.1–7.16
Forma D WRENN AND KOKINOS, 1986, p. 205, pl. 10, fig. 5; p. 211, pl. 13, figs. 2, 3.
Forma D of Wrenn and Kokinos, 1986. HEAD, 1996a, p. 1216; LOUWYE, HEAD, AND DE SCHEPPER, in press, fig. 9l.
? Gen. et sp. indet. HEAD, 1998a, p. 812, fig. 4e.
Diagnosis. - A large, thin-walled species of Desotodinium n. gen. with smooth to weakly ornamented wall surface, outline circular to subcircular in polar view. Thin, equatorial flange sometimes present. Archeopyle comprises three postcingular plates (interpreted as 2’’-4’’) and two antapical plates; otherwise only weak indications of tabulation on hypocyst, and none on epicyst.
Description. - Large, thin-walled (ca. 0.3 µm or less) cyst, polar-compressed; central body circular to subcircular in outline, nearly colorless to light brown. Wall surface smooth, shagreenate to scabrate. Thin diaphanous flange occasionally present with irregular margin, extends around equator. Tabulation expressed by large hypocystal archeopyle, formed by what we interpret as three postcingular plates (2’’, 3’’, and 4’’), and one left first antapical and one right first antapical plate (respectively 1’’’l and 1’’’’l). Archeopyle margin distinctly straight to gently concave on dorsal surface, where delineated by posterior cingular margin. Lateral archeopyle margins usually show small projections between postcingular plates and antapical plates (indicated by arrow on Fig. 7.3, 7.4, 7.6, 7.7, 7.9–7.11). Outward and inward projections along the cingular margin were seen on one specimen: projections of the archeopyle margin towards the cingular series presumably reflect boundaries separating individual cingular plates, whereas projections towards the archeopyle presumably reflect the junction of two postcingular plates with the cingular margin. Postcingular plates 2’’’ and 4’’’ quadrangular, plate 3- typically hypocystal isodelta-camerate to theta-delta-camerate. Irregularly hexagonal antapical plates are approximate mirror images of each other. However, side of plate 1’’’’l that contacts ps? plate is inflected inwards on two observed specimens (Fig. 7.2, 7.3, 7.6, 7.9, 7.11), a feature also possibly present on specimen illustrated by Wrenn and Kokinos (1986, fig. 13.2, as Forma D; see their plate 2’’’’). Plate adjacent to antapical plates on ventral side questionably posterior sulcal plate (ps?) (see Head, 1998b, p. 800). Opercular plates adherent. No other indications of tabulation.
Etymology. - Named for John H. Wrenn in tribute to his studies on Neogene dinoflagellate cysts from the De Soto Canyon.
Type. - Holotype, sample VB3.12, slide p2, England Finder reference W26/1. Basal Shelly Unit, Lillo Formation, Verrebroek Dock; upper Lower or lower Upper Pliocene. Figure 7.1–7.6. Royal Belgian Institute of Natural Sciences, Brussels, registration number IRScN b4255.
Measurements. - Holotype: maximum diameter, 47 µm; no flange present. Range: central body maximum diameter, 47(59.8)67 µm, nine specimens with and without flange measured; maximum width of flange, 22(23)25 µm, three specimens measured.
Occurrence. - Basal Shelly Unit, Oorderen Sands, and Kruisschans Sands members of the Lillo Formation at the Deurganck Dock and Verrebroek Dock; upper Lower and/or lower Upper Pliocene. Questionable recovery from the Upper Pliocene Red Crag Formation in eastern England (as Gen. et sp. indet. in Head, 1998a). Lower Pliocene through Upper Pleistocene of the De Soto Canyon, Gulf of Mexico (as Forma D in Wrenn and Kokinos, 1986).
Comparison. - See for genus; no other species of Desotodinium have yet been identified.
Biological affinity. - Modern cysts of Pyrophacus horologium von Stein, 1883 were documented by Wall and Dale (1971, p. 225, fig. 4d–g). Head (1996a) proposed that Forma D of Wrenn and Kokinos (1986), synonymized here with Desotodinium wrennii, is probably the cyst of Pyrophacus horologium. Our new observations support this likely correlation.
Autecology. - Pyrophacus horologium is an extant cosmopolitan species in tropical to cold-temperate waters, and is found in oceanic, neritic, and estuarine settings (Steidinger and Tangen, 1996). Gayoso (2001) reported the motile stage from the Golfo Nuevo (43 degrees south) on the Patagonian coast of Argentina, an environment semi-isolated from shelfal waters of the southern Atlantic Ocean, where low nutrient concentrations and a salinity of about 34 psu occur. Highest abundances were found during summer (January–February), with sea surface temperatures of about 18 degrees Celsius. It has also been recorded in the Gulf of Finland within the Baltic Sea, where it is considered a relatively warm-water species (Edler et al., 1984), and where salinities are around 10 psu or less.
Discussion. - Our interpretation of the tabulation for Desotodinium wrennii agrees with the interpretation of Wrenn and Kokinos (1986, as Forma D) for the postcingular plates. However, whereas Wrenn and Kokinos recognized a first and second antapical plate (100 and 200, consistent with the standard peridinialean tabulation pattern), we interpret these plates as left and right first antapical plates (1’’’’l and 1’’’’r) that originated from a single antapical plate of the standard gonyaulacalean tabulation pattern. Consequently, we classify Desotodinium wrennii as a gonyaulacalean dinoflagellate and not as a peridinialean. The thin equatorial flange, present on a few specimens, probably preserves only under favorable conditions. Wrenn and Kokinos (1986) also illustrated specimens both with and without an equatorial flange. Gen. et sp. indet. of Head, 1998a (Fig. 7.16) is assigned questionably to Desotodinium wrennii because only four plates could be distinguished within the archeopyle: two postcingular plates and two antapical plates. The typical pentagonal plate 3- seems to be absent. However, the archeopyle margins show small projections towards the archeopyle between postcingular plates and antapical plates, as for Desotodinium wrennii.
Holotype: De Schepper et al., fig.7, nos.1–6.
Age: Pliocene.
Original description (De Schepper):
DESOTODINIUM WRENNII new species Figure 7.1–7.16
Forma D WRENN AND KOKINOS, 1986, p. 205, pl. 10, fig. 5; p. 211, pl. 13, figs. 2, 3.
Forma D of Wrenn and Kokinos, 1986. HEAD, 1996a, p. 1216; LOUWYE, HEAD, AND DE SCHEPPER, in press, fig. 9l.
? Gen. et sp. indet. HEAD, 1998a, p. 812, fig. 4e.
Diagnosis. - A large, thin-walled species of Desotodinium n. gen. with smooth to weakly ornamented wall surface, outline circular to subcircular in polar view. Thin, equatorial flange sometimes present. Archeopyle comprises three postcingular plates (interpreted as 2’’-4’’) and two antapical plates; otherwise only weak indications of tabulation on hypocyst, and none on epicyst.
Description. - Large, thin-walled (ca. 0.3 µm or less) cyst, polar-compressed; central body circular to subcircular in outline, nearly colorless to light brown. Wall surface smooth, shagreenate to scabrate. Thin diaphanous flange occasionally present with irregular margin, extends around equator. Tabulation expressed by large hypocystal archeopyle, formed by what we interpret as three postcingular plates (2’’, 3’’, and 4’’), and one left first antapical and one right first antapical plate (respectively 1’’’l and 1’’’’l). Archeopyle margin distinctly straight to gently concave on dorsal surface, where delineated by posterior cingular margin. Lateral archeopyle margins usually show small projections between postcingular plates and antapical plates (indicated by arrow on Fig. 7.3, 7.4, 7.6, 7.7, 7.9–7.11). Outward and inward projections along the cingular margin were seen on one specimen: projections of the archeopyle margin towards the cingular series presumably reflect boundaries separating individual cingular plates, whereas projections towards the archeopyle presumably reflect the junction of two postcingular plates with the cingular margin. Postcingular plates 2’’’ and 4’’’ quadrangular, plate 3- typically hypocystal isodelta-camerate to theta-delta-camerate. Irregularly hexagonal antapical plates are approximate mirror images of each other. However, side of plate 1’’’’l that contacts ps? plate is inflected inwards on two observed specimens (Fig. 7.2, 7.3, 7.6, 7.9, 7.11), a feature also possibly present on specimen illustrated by Wrenn and Kokinos (1986, fig. 13.2, as Forma D; see their plate 2’’’’). Plate adjacent to antapical plates on ventral side questionably posterior sulcal plate (ps?) (see Head, 1998b, p. 800). Opercular plates adherent. No other indications of tabulation.
Etymology. - Named for John H. Wrenn in tribute to his studies on Neogene dinoflagellate cysts from the De Soto Canyon.
Type. - Holotype, sample VB3.12, slide p2, England Finder reference W26/1. Basal Shelly Unit, Lillo Formation, Verrebroek Dock; upper Lower or lower Upper Pliocene. Figure 7.1–7.6. Royal Belgian Institute of Natural Sciences, Brussels, registration number IRScN b4255.
Measurements. - Holotype: maximum diameter, 47 µm; no flange present. Range: central body maximum diameter, 47(59.8)67 µm, nine specimens with and without flange measured; maximum width of flange, 22(23)25 µm, three specimens measured.
Occurrence. - Basal Shelly Unit, Oorderen Sands, and Kruisschans Sands members of the Lillo Formation at the Deurganck Dock and Verrebroek Dock; upper Lower and/or lower Upper Pliocene. Questionable recovery from the Upper Pliocene Red Crag Formation in eastern England (as Gen. et sp. indet. in Head, 1998a). Lower Pliocene through Upper Pleistocene of the De Soto Canyon, Gulf of Mexico (as Forma D in Wrenn and Kokinos, 1986).
Comparison. - See for genus; no other species of Desotodinium have yet been identified.
Biological affinity. - Modern cysts of Pyrophacus horologium von Stein, 1883 were documented by Wall and Dale (1971, p. 225, fig. 4d–g). Head (1996a) proposed that Forma D of Wrenn and Kokinos (1986), synonymized here with Desotodinium wrennii, is probably the cyst of Pyrophacus horologium. Our new observations support this likely correlation.
Autecology. - Pyrophacus horologium is an extant cosmopolitan species in tropical to cold-temperate waters, and is found in oceanic, neritic, and estuarine settings (Steidinger and Tangen, 1996). Gayoso (2001) reported the motile stage from the Golfo Nuevo (43 degrees south) on the Patagonian coast of Argentina, an environment semi-isolated from shelfal waters of the southern Atlantic Ocean, where low nutrient concentrations and a salinity of about 34 psu occur. Highest abundances were found during summer (January–February), with sea surface temperatures of about 18 degrees Celsius. It has also been recorded in the Gulf of Finland within the Baltic Sea, where it is considered a relatively warm-water species (Edler et al., 1984), and where salinities are around 10 psu or less.
Discussion. - Our interpretation of the tabulation for Desotodinium wrennii agrees with the interpretation of Wrenn and Kokinos (1986, as Forma D) for the postcingular plates. However, whereas Wrenn and Kokinos recognized a first and second antapical plate (100 and 200, consistent with the standard peridinialean tabulation pattern), we interpret these plates as left and right first antapical plates (1’’’’l and 1’’’’r) that originated from a single antapical plate of the standard gonyaulacalean tabulation pattern. Consequently, we classify Desotodinium wrennii as a gonyaulacalean dinoflagellate and not as a peridinialean. The thin equatorial flange, present on a few specimens, probably preserves only under favorable conditions. Wrenn and Kokinos (1986) also illustrated specimens both with and without an equatorial flange. Gen. et sp. indet. of Head, 1998a (Fig. 7.16) is assigned questionably to Desotodinium wrennii because only four plates could be distinguished within the archeopyle: two postcingular plates and two antapical plates. The typical pentagonal plate 3- seems to be absent. However, the archeopyle margins show small projections towards the archeopyle between postcingular plates and antapical plates, as for Desotodinium wrennii.