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Dalella chathamensis
Dalella chathamensis McMinn and Sun Xuekun, 1994, p.43,45, pl.1, figs.1-12; text-figs.2A-C. Holotype: McMinn and Sun Xuekun, 1994, pl.1, figs.1-3. Age: Holocene.
Derivation of name: named after the type locality, Chatham Rise, east of New Zealand. Holotype: Plate 1, figs, 1-3; Holocene; DSDP Site 594-1X-1, 44 cm, east of New Zealand, Catalogue Number UTGD 124957.
Diagnosis: Gonyaulacacean taxa with a sexiform, S-type paratabulation. Subspherical cyst comprised of an autophragm and a trabeculum. Trabeculum is joined to autocyst at parasulcus, archeopyle margin and the apex. Archeopyle is precingular, Type P (3’’ only); operculum is detached. Paratabulation is gonyaulacean.
Description: Subspherical cyst comprised of a 1-2 μm thick autophragm and a trabeculum. The auto phragm is finely granulate to laevigate. The trabeculum is comprised of ribbon-like threads with a central thickened ridge. It is joined directly to the autocyst at the parasulcus and the archeopyle margin. At the apex it is connected to the autocyst by a single apical process. Only the dorsal paratabultaion is outlines by trabeculum and here the 2’’,3’’, 4’’, 3c, 4c, 3’’’and 1’’’’ paraplates can be distinguished (Text Figure 2a). The apical paraplates are differentiated on the dorsal surface by the upper margins of the 2’’, 3’’ and 4’’ paraplates. ; there is no differentiation of paraplates within the apical series. The dorsal precingular paraplates are standard gonyaulacean in shape. 3c and 4c paraplates are distinctly hexagonal and thus resemble those of Spiniferites. The only other paraplates clearly distinguishable are the 4’’’and 1’’’’,which both conform in size and shape to other gonyaulacean, sexiform, S-type taxa. The outline of the dorsal paratabular trabeculas strands forms a ring around the autocyst. This is connected to a second ring, which is joined to the first at the apax, the antapical paraplate and the paracingulum (text Figure 2c). Eight trabecular strands joint this second ring to the vental surface in the vicinity of the parasulcus (Taxt Figure 2b). The autocyst contains no indication of paratabulation other than the archeopyle and the apical processes. The archeopyle is prengular, Type P (3’’ only) and the operculum is detached. Paracingulum is clearly indicated by elongate lumina in the trabeculum. No detailed parasulcal paratabulation can be recognized.
Dimensions: Holotype – Overall diameter 78 μm, body diameter 35 μm; Range – Overall diameter 48(61)78 μm, body diameter 18(25)35 μm; 20 specimens measured.
Comparison: Although there are no previous, unambiguous records of this taxa, a number of published illustrations of similar specimens have been recorded. Head et al. (1989; Pl. 4, figs 1, 2, 4) described a form from the upper Miocene, which was informally reffered to as “gen. et sp. indet.”. This taxon differs from D. chathamense in having an elongate autocyst and seemingly far fewer trabecular thread. The illustration of ?Evittosphaerula sp. by Manum et al. (1989; Pl. 7, figs. 8-10) from the Pliocene is similar in appearance but is too poorly preserved to determine whether it is conspecific, and the specimen illustrated by Matsuoka and Bujak (1988; Pl. 3, fig 2) as ?Evittosphaerula sp. A. has many more trabelucar threads than D. chathamense. Occurrence: This taxa was recorded from only two samples from north of the STC but comprised an average of 6.6% of those from the south. It was recorded as gen. et sp. indet. From DSDP 594 and surface sediments around the Chatham Rise, east of New Zealand (Sun and McMinn, 1994) and has subsequently also been reported from surface and Quaternary samples from weatern Tasmania (McMinn, unpubl. data).
Derivation of name: named after the type locality, Chatham Rise, east of New Zealand. Holotype: Plate 1, figs, 1-3; Holocene; DSDP Site 594-1X-1, 44 cm, east of New Zealand, Catalogue Number UTGD 124957.
Diagnosis: Gonyaulacacean taxa with a sexiform, S-type paratabulation. Subspherical cyst comprised of an autophragm and a trabeculum. Trabeculum is joined to autocyst at parasulcus, archeopyle margin and the apex. Archeopyle is precingular, Type P (3’’ only); operculum is detached. Paratabulation is gonyaulacean.
Description: Subspherical cyst comprised of a 1-2 μm thick autophragm and a trabeculum. The auto phragm is finely granulate to laevigate. The trabeculum is comprised of ribbon-like threads with a central thickened ridge. It is joined directly to the autocyst at the parasulcus and the archeopyle margin. At the apex it is connected to the autocyst by a single apical process. Only the dorsal paratabultaion is outlines by trabeculum and here the 2’’,3’’, 4’’, 3c, 4c, 3’’’and 1’’’’ paraplates can be distinguished (Text Figure 2a). The apical paraplates are differentiated on the dorsal surface by the upper margins of the 2’’, 3’’ and 4’’ paraplates. ; there is no differentiation of paraplates within the apical series. The dorsal precingular paraplates are standard gonyaulacean in shape. 3c and 4c paraplates are distinctly hexagonal and thus resemble those of Spiniferites. The only other paraplates clearly distinguishable are the 4’’’and 1’’’’,which both conform in size and shape to other gonyaulacean, sexiform, S-type taxa. The outline of the dorsal paratabular trabeculas strands forms a ring around the autocyst. This is connected to a second ring, which is joined to the first at the apax, the antapical paraplate and the paracingulum (text Figure 2c). Eight trabecular strands joint this second ring to the vental surface in the vicinity of the parasulcus (Taxt Figure 2b). The autocyst contains no indication of paratabulation other than the archeopyle and the apical processes. The archeopyle is prengular, Type P (3’’ only) and the operculum is detached. Paracingulum is clearly indicated by elongate lumina in the trabeculum. No detailed parasulcal paratabulation can be recognized.
Dimensions: Holotype – Overall diameter 78 μm, body diameter 35 μm; Range – Overall diameter 48(61)78 μm, body diameter 18(25)35 μm; 20 specimens measured.
Comparison: Although there are no previous, unambiguous records of this taxa, a number of published illustrations of similar specimens have been recorded. Head et al. (1989; Pl. 4, figs 1, 2, 4) described a form from the upper Miocene, which was informally reffered to as “gen. et sp. indet.”. This taxon differs from D. chathamense in having an elongate autocyst and seemingly far fewer trabecular thread. The illustration of ?Evittosphaerula sp. by Manum et al. (1989; Pl. 7, figs. 8-10) from the Pliocene is similar in appearance but is too poorly preserved to determine whether it is conspecific, and the specimen illustrated by Matsuoka and Bujak (1988; Pl. 3, fig 2) as ?Evittosphaerula sp. A. has many more trabelucar threads than D. chathamense. Occurrence: This taxa was recorded from only two samples from north of the STC but comprised an average of 6.6% of those from the south. It was recorded as gen. et sp. indet. From DSDP 594 and surface sediments around the Chatham Rise, east of New Zealand (Sun and McMinn, 1994) and has subsequently also been reported from surface and Quaternary samples from weatern Tasmania (McMinn, unpubl. data).