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Selenopemphix minusa
Selenopemphix minusa Harland and Pudsey, 2002, p.278–279, pl.4, figs.5–7. Holotype: Harland and Pudsey, 2002, pl.4, fig.7. Based on Greek, this epithet is correctly rendered as minusa when feminine, minys (as cited in Harland and Pudsey) when masculine, and minym when neuter. Age: late Miocene.
Original description (Harland & Pudsey, 2002)
Derivation of name: Greek, minys, little, small and short; with reference to the particularly small size of this species.
Diagnosis: A small dinoflagellate cyst occurring preferentially in polar compression. Cyst light brown and consists of an undifferentiated wall only. Paratabulation expressed by the paracingulum, parasulcus and archaeopyle. Paracingulum planar and demarcated by sutural membranes that are generally smooth and low but also with minor faint striations and crenulate margins. Archaeopyle monoplacoid, asymmetrically placed, offset to the left, steno-deltaform and formed by loss of the presumed 2a intercalary paraplate. Operculum free and simple.
Description: This small dinoflagellate cyst was always observed in polar compression with a rounded reniform outline. The cyst wall appears to be made up of a single undifferentiated layer and is a light brown in colour. The wall is usually smooth but may exhibit grana. The paracingular sutures, the parasulcus and the opening of the archaeopyle demonstrate a part of the paratabulation. The paracingulum occurs around the circumference of the cyst and is outlined by sutural membranes that are smooth, low i.e. less than 1 μm, with some minor, faint striations and some minor crenulations that are often difficult to observe. The paracingulum is planar, not exhibiting any evidence of marked offset. It is possible that additional sutural membranes may provide further evidence of the paratabulation, but on the specimens observed difficulty was experienced in differentiating these possible sutural membranes from folds in the cyst wall. The archaeopyle is monoplacoid and offset to the left of from the dorso-ventral axis of the cyst. It opens by the presumed loss of a single intercalary plate, the 2a, which is free, simple and probably steno-deltaform with an archaeopyle ratio of >1.0 and an archaeopyle signum of <1.0. The operculum may still be in place in some specimens. The shape of the archaeopyle is consistent with a hexa peridiniacean paratabulation; detail of the topology of the first apical paraplate was not available.
Nomenclatural type: The holotype is Specimen No. R.8001.21, Plate IV, 7, slide RH 310A, ODP 1095B-29X-4, 63–65, England Finder R47/3 and is lodged in the collections of the British Antarctic Survey, Cambridge. Age: Late Miocene at 8.05 Ma.
Dimensions: Holotype, maximum dimension (along the dorso-ventral axis) 38 μm, minimum dimension (between the lateral sides of the cyst and at right angles to the dorso-ventral axis) 36 μm.
Range, maximum length (usually between the lateral sides of the cyst in polar compression) 38(43.7)48 μm, minimum length (usually between the dorsal and ventral surfaces of the cyst in polar compression) 33(38.0)44 μm. Six specimens measured.
Remarks: This new species is characterised by its small size and the minor, often obscure, crenulations along the paracingular sutures. In these two respects it is significantly different from all other species of Selenopemphix and despite the low numbers of individuals seen is erected here as a new species. This taxon only appears to occur in polar compression as no examples of a dorso-ventral compression were recognised in the assemblages.
Occurrence: This species was recorded from samples RH308, RH 310, RH 311, RH 399 and RH 400, Late Miocene and may well have been included in both the Selenopemphix sp. A and Selenopemphix sp. indet. counts of Pudsey and Harland (2001), before a full taxonomic review was undertaken. The samples encompass sediments dated between 7.15 and 8.64 Ma.
Original description (Harland & Pudsey, 2002)
Derivation of name: Greek, minys, little, small and short; with reference to the particularly small size of this species.
Diagnosis: A small dinoflagellate cyst occurring preferentially in polar compression. Cyst light brown and consists of an undifferentiated wall only. Paratabulation expressed by the paracingulum, parasulcus and archaeopyle. Paracingulum planar and demarcated by sutural membranes that are generally smooth and low but also with minor faint striations and crenulate margins. Archaeopyle monoplacoid, asymmetrically placed, offset to the left, steno-deltaform and formed by loss of the presumed 2a intercalary paraplate. Operculum free and simple.
Description: This small dinoflagellate cyst was always observed in polar compression with a rounded reniform outline. The cyst wall appears to be made up of a single undifferentiated layer and is a light brown in colour. The wall is usually smooth but may exhibit grana. The paracingular sutures, the parasulcus and the opening of the archaeopyle demonstrate a part of the paratabulation. The paracingulum occurs around the circumference of the cyst and is outlined by sutural membranes that are smooth, low i.e. less than 1 μm, with some minor, faint striations and some minor crenulations that are often difficult to observe. The paracingulum is planar, not exhibiting any evidence of marked offset. It is possible that additional sutural membranes may provide further evidence of the paratabulation, but on the specimens observed difficulty was experienced in differentiating these possible sutural membranes from folds in the cyst wall. The archaeopyle is monoplacoid and offset to the left of from the dorso-ventral axis of the cyst. It opens by the presumed loss of a single intercalary plate, the 2a, which is free, simple and probably steno-deltaform with an archaeopyle ratio of >1.0 and an archaeopyle signum of <1.0. The operculum may still be in place in some specimens. The shape of the archaeopyle is consistent with a hexa peridiniacean paratabulation; detail of the topology of the first apical paraplate was not available.
Nomenclatural type: The holotype is Specimen No. R.8001.21, Plate IV, 7, slide RH 310A, ODP 1095B-29X-4, 63–65, England Finder R47/3 and is lodged in the collections of the British Antarctic Survey, Cambridge. Age: Late Miocene at 8.05 Ma.
Dimensions: Holotype, maximum dimension (along the dorso-ventral axis) 38 μm, minimum dimension (between the lateral sides of the cyst and at right angles to the dorso-ventral axis) 36 μm.
Range, maximum length (usually between the lateral sides of the cyst in polar compression) 38(43.7)48 μm, minimum length (usually between the dorsal and ventral surfaces of the cyst in polar compression) 33(38.0)44 μm. Six specimens measured.
Remarks: This new species is characterised by its small size and the minor, often obscure, crenulations along the paracingular sutures. In these two respects it is significantly different from all other species of Selenopemphix and despite the low numbers of individuals seen is erected here as a new species. This taxon only appears to occur in polar compression as no examples of a dorso-ventral compression were recognised in the assemblages.
Occurrence: This species was recorded from samples RH308, RH 310, RH 311, RH 399 and RH 400, Late Miocene and may well have been included in both the Selenopemphix sp. A and Selenopemphix sp. indet. counts of Pudsey and Harland (2001), before a full taxonomic review was undertaken. The samples encompass sediments dated between 7.15 and 8.64 Ma.