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Spinidinium luciae
Spinidinium luciae Wrenn and Hart, 1988, p.368, fig.35, nos.1–3, fig.38, nos.1–5; fig.39, no.4.
Originally (and now) Spinidinium, subsequently Volkheimeridium.
Sluijs et al. (2009, p.47) retained this species in Spinidinium.
Holotype: Wrenn and Hart, 1988, fig.35, nos.1–3.
Age: early Eocene
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Original description: [Wrenn and Hart, 1988]:
Spinidinium luciae sp. nov.
Figures 35.1-3, 38.1-5, 39.4
Diagnosis. A species of Spinidiniam that is characterized by penitabular and parasutural denticulate crests or rows of isolated denticles. The
attenuated intercalary 2a archeopyle may have a free or posteriorly adherent operculum. Accessory parasutures may be developed along the
lateral margins of the 4" paraplate (i.e., the 3"/4" and the 4"/5" parasutures).
Description.
Shape: The pericyst outline is subpentagonal to subhexagonal, depending on the distal width of the apical horn. The subtriangular epicyst
is terminated by a short, truncated apical horn that often is concave distally. Penitabular or parasutural denticulate crests or rows of individual denticles give the dinocyst margin a serrate appearance. Two lateral transapical crests, each bearing a row of denticles, run from the paracingulum over the apex of the apical horn and down to the paracingulum on the other side. The denticles may be distally rounded or pointed. The subrectangular hypocyst is approximately half the length of the epicyst. It is flattened antapically, but short, unequal antapical horns may be present. The left antapical horn is always more fully developed than is the right antapical horn, which may not be developed at all. The horns vary in shape from subrounded to sharp, spike-like protuberances. The pericyst is broadest in the paracingular region. The endocyst outline is subrounded to subpentagonal and often mimics the outline of the pericyst.
Phragma: Cysts are circumcavate to cornuncavate. The periphragm is approximately 0.5 μm thick and may be shagreenate or uniformly granulate. The granules vary in size, but they are always smaller than the 1- to 3-μm-high denticles capping the penitabular or parasutural crests. The endophragm is shagreenate to scabbrate and approximatcly 1 μm thick.
Paratabulation: Paratabulation is expressed on the pericyst by denticulate to serrate crests or isolated denticles. Penitabular rows of denticles delimit all paraplates, except perhaps along the margins of the parasulcus. Parasutural denticles cap the ridges bordering the paracingulum. The penitabular denticles are poorly developed in the parasulcal area. Ventral paratabulation similar to ortho epithecal tabulation. The
paratabulation formula is 4', 3a, 7", 5-7C, 5"', ?2"". The only indication of paratabulation on the endocyst is the 2a intercalary archeopyle.
Paracingulum: The lacvorotatory paracingulum is bordered by two discontinuous parallel denticulate to serrate parasutural crests. The ends
of the paracingulum are offset less than one full width of the paracingulum. The discontinuous paracingular crests and/or denticles divide the
paracingulum into five to seven paraplates.
Parasulcus: The parasulcus is delimited by denticulate to serrate crests that are less well developed and less continuous than those bordering the paracingulum. The parasulcus is broadest posteriorly and tapers anteriorly, where it runs well up onto the epicyst. A single, large denticle in the right, middle area of the parasulcus may reflect the location of the flagellar pore of the theca. The parasulcus is not expressed on the endocyst.
Archeopyle: Archeopyle type 1/I. The operculum of the attenuated 2a archeopyle may be free or adherent along the H4 parasuture. The lateral parasutures of the 4" paraplate (i.e., 3"/4" and 4"/5") may be partially open, but the 4" is adnate along the anterior margin of the paracingulum. The 4" may or may not be involved in archeopyle formation; when 4" is involved, it is probably fortuitous.
Dimensions. Observed range (10 specimens): pericyst length, 51 to 87 μm (mean, 64 μm); pericyst width, 46 to 76 μm (mean, 61 μm); endocyst length, 45 to 66 μm (mean, 52 μm); endocyst width, 42 to 56 μm (mean, 46 μm); archeopyle dimensions (6 specimens): length, 16 to 32 μm (mean, 20 μm); width, 16 to 21 μm (mean, 19 μm); periphragm, approximately 0.5 μm thick; endophragm, 0.75 to 1.0 μm thick.
Discussion. The endocyst varies considerably in shape and size. Consequently, the relationship between the periarcheopyle and the epipericoel
also varies. The epipericoel is in communication with the exterior through the intercalary periarcheopyle only on specimens bearing a circular endocyst. Communication is reduced or totally blocked by an elongate endocyst that mimics the outline of the pericyst. The denticulate
to serrate transapical crests form distinctive crescent-shaped depressions at the apex of the apical horn.
Comparison with Similar Species. The denticulate parallel transapical crests and the variable archeopyle distinguish Spinidinium luciae sp. nov.
from all other dinocysts. In particular, S. luciae sp. nov. differs from: S. Styloniferum by having fewer, stouter and distally rounded denticules
rather than spines; from S. macmurdoensis and S. sverdrupianum in overall cyst shape and in the type and distribution of ornamentation; and
from Chichaouadinium vestitum and C. boydii by the type and distribution of ornamentation, in overall shape and archeopyle development.
Holotype. Slide 8452, E/1, 118.3 x 11.4 (L23). Sample 8452, Section 3, La Meseta Formation, late carly Eocene, Seymour Island, Antarctica.
Derivation of Name. Named in memory of the senior author's sister, Lucielle Jeni Wrenn Bjorgo.
Stratigraphic Occurrence. La Meseta Formation (Section 3, Eocene; Sections 18 and 19, Eocene).
Originally (and now) Spinidinium, subsequently Volkheimeridium.
Sluijs et al. (2009, p.47) retained this species in Spinidinium.
Holotype: Wrenn and Hart, 1988, fig.35, nos.1–3.
Age: early Eocene
------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Wrenn and Hart, 1988]:
Spinidinium luciae sp. nov.
Figures 35.1-3, 38.1-5, 39.4
Diagnosis. A species of Spinidiniam that is characterized by penitabular and parasutural denticulate crests or rows of isolated denticles. The
attenuated intercalary 2a archeopyle may have a free or posteriorly adherent operculum. Accessory parasutures may be developed along the
lateral margins of the 4" paraplate (i.e., the 3"/4" and the 4"/5" parasutures).
Description.
Shape: The pericyst outline is subpentagonal to subhexagonal, depending on the distal width of the apical horn. The subtriangular epicyst
is terminated by a short, truncated apical horn that often is concave distally. Penitabular or parasutural denticulate crests or rows of individual denticles give the dinocyst margin a serrate appearance. Two lateral transapical crests, each bearing a row of denticles, run from the paracingulum over the apex of the apical horn and down to the paracingulum on the other side. The denticles may be distally rounded or pointed. The subrectangular hypocyst is approximately half the length of the epicyst. It is flattened antapically, but short, unequal antapical horns may be present. The left antapical horn is always more fully developed than is the right antapical horn, which may not be developed at all. The horns vary in shape from subrounded to sharp, spike-like protuberances. The pericyst is broadest in the paracingular region. The endocyst outline is subrounded to subpentagonal and often mimics the outline of the pericyst.
Phragma: Cysts are circumcavate to cornuncavate. The periphragm is approximately 0.5 μm thick and may be shagreenate or uniformly granulate. The granules vary in size, but they are always smaller than the 1- to 3-μm-high denticles capping the penitabular or parasutural crests. The endophragm is shagreenate to scabbrate and approximatcly 1 μm thick.
Paratabulation: Paratabulation is expressed on the pericyst by denticulate to serrate crests or isolated denticles. Penitabular rows of denticles delimit all paraplates, except perhaps along the margins of the parasulcus. Parasutural denticles cap the ridges bordering the paracingulum. The penitabular denticles are poorly developed in the parasulcal area. Ventral paratabulation similar to ortho epithecal tabulation. The
paratabulation formula is 4', 3a, 7", 5-7C, 5"', ?2"". The only indication of paratabulation on the endocyst is the 2a intercalary archeopyle.
Paracingulum: The lacvorotatory paracingulum is bordered by two discontinuous parallel denticulate to serrate parasutural crests. The ends
of the paracingulum are offset less than one full width of the paracingulum. The discontinuous paracingular crests and/or denticles divide the
paracingulum into five to seven paraplates.
Parasulcus: The parasulcus is delimited by denticulate to serrate crests that are less well developed and less continuous than those bordering the paracingulum. The parasulcus is broadest posteriorly and tapers anteriorly, where it runs well up onto the epicyst. A single, large denticle in the right, middle area of the parasulcus may reflect the location of the flagellar pore of the theca. The parasulcus is not expressed on the endocyst.
Archeopyle: Archeopyle type 1/I. The operculum of the attenuated 2a archeopyle may be free or adherent along the H4 parasuture. The lateral parasutures of the 4" paraplate (i.e., 3"/4" and 4"/5") may be partially open, but the 4" is adnate along the anterior margin of the paracingulum. The 4" may or may not be involved in archeopyle formation; when 4" is involved, it is probably fortuitous.
Dimensions. Observed range (10 specimens): pericyst length, 51 to 87 μm (mean, 64 μm); pericyst width, 46 to 76 μm (mean, 61 μm); endocyst length, 45 to 66 μm (mean, 52 μm); endocyst width, 42 to 56 μm (mean, 46 μm); archeopyle dimensions (6 specimens): length, 16 to 32 μm (mean, 20 μm); width, 16 to 21 μm (mean, 19 μm); periphragm, approximately 0.5 μm thick; endophragm, 0.75 to 1.0 μm thick.
Discussion. The endocyst varies considerably in shape and size. Consequently, the relationship between the periarcheopyle and the epipericoel
also varies. The epipericoel is in communication with the exterior through the intercalary periarcheopyle only on specimens bearing a circular endocyst. Communication is reduced or totally blocked by an elongate endocyst that mimics the outline of the pericyst. The denticulate
to serrate transapical crests form distinctive crescent-shaped depressions at the apex of the apical horn.
Comparison with Similar Species. The denticulate parallel transapical crests and the variable archeopyle distinguish Spinidinium luciae sp. nov.
from all other dinocysts. In particular, S. luciae sp. nov. differs from: S. Styloniferum by having fewer, stouter and distally rounded denticules
rather than spines; from S. macmurdoensis and S. sverdrupianum in overall cyst shape and in the type and distribution of ornamentation; and
from Chichaouadinium vestitum and C. boydii by the type and distribution of ornamentation, in overall shape and archeopyle development.
Holotype. Slide 8452, E/1, 118.3 x 11.4 (L23). Sample 8452, Section 3, La Meseta Formation, late carly Eocene, Seymour Island, Antarctica.
Derivation of Name. Named in memory of the senior author's sister, Lucielle Jeni Wrenn Bjorgo.
Stratigraphic Occurrence. La Meseta Formation (Section 3, Eocene; Sections 18 and 19, Eocene).