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Nelsoniella incomposita
Nelsoniella incomposita Pearce, 2010, p.68, pl.5, figs.8–11.
Holotype: Pearce, 2010, pl.5, figs.8–9,11.
Type location and horizon. Trunch borehole, Norfolk, UK; 213.9–214.0 m, Burnham–Flamborough Chalk (undifferentiated), high Gonioteuthis quadrata Zone (high lower Campanian).
Age: Campanian.
Diagnosis. A species of Nelsoniella possessing verrucae on the ventral epitheca that may be isolated or coalesce into irregular ridges or patches.
Description (Pearce, 2010). Large compressed sub-spherical epicavate dinoflagellate cyst with a short apical horn. The wall is two-layered, comprised of a thin (usually less than 0.5 μm but up to 1 μm) and smooth to finely granular endophragm and a periphragm of variable thickness (1–2 μm) being thickest at the antapex and often the apex. The periphragm is ornamented by verrucae that are either isolated or fused into discontinuous and wavy ridges with no clear or consistent pattern, generally restricted to the
ventral surface of the epicyst. The endocyst is confined to the hypocyst, appressed to the periphragm in the hypocystal region and comprises one-half to two-thirds the dinocyst length, and resulting in a wide epi-pericoel. The pericyst forms a short apical horn of variable length that is often concave at the apex and may possess ridges that pass from the edge of the apical horn
onto the dorsal epicyst. The peri-archaeopyle is isodeltaform with a transverse archaeopyle index of 0.4–0.5 (as typical of genus, operculum detached). The endo-archaeopyle type has not been determined.
Comparison. Nelsoniella aceras Cookson & Eisenack (1960: 4, pl. 1, figs 12–13) lacks a prominent apical horn and is deeply concave at the extreme apex, Nelsoniella oviformis Cookson & Eisenack (1982: 33, pl. 3, fig. 2) possesses a strong apical horn but the cyst is clearly longer than broad with a weakly smooth to clearly granulated periphragm. Nelsoniella semireticulata Cookson & Eisenack (1960: 4–5, pl. 1, fig. 15) is ornamented on the epicyst ventral surface with a low, thin-walled reticulum. Nelsoniella tuberculata Cookson & Eisenack (1960: 4, pl. 1, fig. 14) has an epitheca ornamented with small tubercles or large granules, but which do not coalesce as frequently or as randomly as in N. incomposita sp. nov.
Holotype: Pearce, 2010, pl.5, figs.8–9,11.
Type location and horizon. Trunch borehole, Norfolk, UK; 213.9–214.0 m, Burnham–Flamborough Chalk (undifferentiated), high Gonioteuthis quadrata Zone (high lower Campanian).
Age: Campanian.
Diagnosis. A species of Nelsoniella possessing verrucae on the ventral epitheca that may be isolated or coalesce into irregular ridges or patches.
Description (Pearce, 2010). Large compressed sub-spherical epicavate dinoflagellate cyst with a short apical horn. The wall is two-layered, comprised of a thin (usually less than 0.5 μm but up to 1 μm) and smooth to finely granular endophragm and a periphragm of variable thickness (1–2 μm) being thickest at the antapex and often the apex. The periphragm is ornamented by verrucae that are either isolated or fused into discontinuous and wavy ridges with no clear or consistent pattern, generally restricted to the
ventral surface of the epicyst. The endocyst is confined to the hypocyst, appressed to the periphragm in the hypocystal region and comprises one-half to two-thirds the dinocyst length, and resulting in a wide epi-pericoel. The pericyst forms a short apical horn of variable length that is often concave at the apex and may possess ridges that pass from the edge of the apical horn
onto the dorsal epicyst. The peri-archaeopyle is isodeltaform with a transverse archaeopyle index of 0.4–0.5 (as typical of genus, operculum detached). The endo-archaeopyle type has not been determined.
Comparison. Nelsoniella aceras Cookson & Eisenack (1960: 4, pl. 1, figs 12–13) lacks a prominent apical horn and is deeply concave at the extreme apex, Nelsoniella oviformis Cookson & Eisenack (1982: 33, pl. 3, fig. 2) possesses a strong apical horn but the cyst is clearly longer than broad with a weakly smooth to clearly granulated periphragm. Nelsoniella semireticulata Cookson & Eisenack (1960: 4–5, pl. 1, fig. 15) is ornamented on the epicyst ventral surface with a low, thin-walled reticulum. Nelsoniella tuberculata Cookson & Eisenack (1960: 4, pl. 1, fig. 14) has an epitheca ornamented with small tubercles or large granules, but which do not coalesce as frequently or as randomly as in N. incomposita sp. nov.