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Nyktericysta davisii
Nyktericysta davisii Bint, 1986
Holotype: Bint, 1986, pl.4, figs.1-2, 5-6, text-fig.3a-b
Locus typicus: Western Interior, U.S.A.
Stratum typicum: Middle-Late Albian
Original description: Bint, 1986, p.149-150
Intermediate to large, dorso-ventrally compressed cysts with tapering, narrowly blunted apical horn, two pointed antapical horns, and two broad, blunt lateral horns from which arise pointed pre- and postcingular extensions. Left antapical horn is slightly larger than right. When deterrninable the left lateral horn is also slightly larger in overall size than the right. On any one lateral horn the precingular extension may be equal in size to or shorter than the postcingular extension. The lateral horns are variable in size and on rare specimens may be reduced to low, rounded bulges bearing very small pre- and postcingular extensions.
Cysts two-layered although this is often difficult to discern. Endocyst produced into five prominent horns: apical and two antapical horns are long and tapering; lateral horns are broad and blunt, with long, short, or absent pre- and postcingular extensions. In all horn terminations the endocyst is rounded. Periphragm is appressed to endophragm over entire cyst surface except at the apical horn tip in some specimens where it may enclose a small pericoel. The other six terminations usually consist of a solid, pointed, rod-like projection but rare specimens may have a pericoel present in the tip of one or more of the lateral extensions. The solid projections are composed of periphragm only which is drawn out beyond the rounded termination of the endophragm. Endophragm smooth or very finely pitted, periphragm finely perforate, and bearing parasutural ridges in some specimens. Perforations are usually about 0.3 µm across but range from 01.0.8 µm. Both walls are very thin, about 0.2 µm each.
Typically paratabulation is lacking, cingulum is indicated by indentation of the lateral horns and faint to distinct transverse lines, and sulcus is not indicated. Some specimens have a ceratioid paratabulation expressed to varying degrees by low parasutural ridges. Fully paratabulate specimens are rare and have an observed paratabulation formula of 4", 6", Sc, 6"", I p, I ""; the sulcus is not divided. In the apical series, paraplate 4" (Taylor-Evitt paraplate A) is rhombic and fails to reach the apex. In the precingular series, I " (2) is reduced in height and the anterior part of 2" (3) extends onto the ventral side and contacts the first apical paraplate ( I u). Also, 3" (4) is not centered on the dorsal midline but is offset to the right. Paraplates 6" (li), 5c (fi), and 6""" (VIu) lie to the right of the sulcus within a defined ventral area which is rarely subdivided; the anterior margin of 6" ( 1 i) is rounded and mid-ventral. There are four cingular paraplates outside the ventral area; lc (au) is left ventral, 2c (b+c) and 3c (d) span the entire dorsal surface and share a mid-dorsal boundary, and 4c (e) is right ventral. The shape of 5c (fi) is not fully known but it has a gently sinuous shape and widens from right to left as it crosses the ventral area. Postcingular paraplate 3""" (IV), instead of being centered on the dorsal midline, is offset to the left; 5""" (VIi) forms not only part of the right lateral horn, but also part of the right antapical horn. 6""" (VIu) lies within the ventral area and is of uncertain shape. The antapical paraplate (Y) is mostly dorsal. The sulcus is narrow, undivided, inclined to the longitudinal axis, and extends almost to the antapical concavity.
The apical horn is composed of three paraplates and often appears to bear a small preapical protrusion at its narrowly blunted tip. Each antapical horn is formed by two paraplates, but in each case the horn tip is formed only from paraplate 1""""(Y), the dorsal component of the horn. The lateral horns are formed from precingular, cingular, and postcingular paraplates. Each pre- and postcingular extension is composed of two paraplates, but the tip is again formed from only the dorsal component paraplate.
Archeopyle apical, operculum adnate ventrally, but often broken away. Archeopyle suture weakly angular to zigzag. In paratabulate forms the suture follows the boundary between apicals 2" (B) and 3" (C) and their subjacent precingulars 2"-5" (3-6), terminating at the triple junctions 1"/2"/2" (lu/B/3) and 3"/4"/5" (C/A/6). There is no archeopyle suture mid-ventrally between apicals 1" (1u) and 4" (A) and their subjacent precingular paraplates; this represents the locus of adnation of the operculum.
Size. Length of complete specimen 88(98)107 µm, 15 measurements; length with operculum broken away 65-79 µm, 5 measurements; width 60(66)76 µm; 20 specimens measured. Approximate lengths of horns: apical 23-30 µm, precingular 1-16 µm, postcingular 2-17 µm, left antapical 15-32 µm, right antapical 10-26 µm; distance between apex of endocyst and apical horn tip 4-8 µm.
Affinities:
Bint, 1986, p.153: Nyktericysta davisii differs from N. pannosa in lacking the granular to spinose ornament of that species. N. arachnion is distinguished from N. davisii by having the periphragm partially separated from the endophragm in a reticulate pattern over the cyst body and also in having cornucavations under the horn tips. Muderongia sp. A and M. sp. B illustrated by May (1979) undoubtedly belong in Nyktericysta and both are quite similar to N. davisii, but further comparison is not possible because descriptions were not given.
Holotype: Bint, 1986, pl.4, figs.1-2, 5-6, text-fig.3a-b
Locus typicus: Western Interior, U.S.A.
Stratum typicum: Middle-Late Albian
Original description: Bint, 1986, p.149-150
Intermediate to large, dorso-ventrally compressed cysts with tapering, narrowly blunted apical horn, two pointed antapical horns, and two broad, blunt lateral horns from which arise pointed pre- and postcingular extensions. Left antapical horn is slightly larger than right. When deterrninable the left lateral horn is also slightly larger in overall size than the right. On any one lateral horn the precingular extension may be equal in size to or shorter than the postcingular extension. The lateral horns are variable in size and on rare specimens may be reduced to low, rounded bulges bearing very small pre- and postcingular extensions.
Cysts two-layered although this is often difficult to discern. Endocyst produced into five prominent horns: apical and two antapical horns are long and tapering; lateral horns are broad and blunt, with long, short, or absent pre- and postcingular extensions. In all horn terminations the endocyst is rounded. Periphragm is appressed to endophragm over entire cyst surface except at the apical horn tip in some specimens where it may enclose a small pericoel. The other six terminations usually consist of a solid, pointed, rod-like projection but rare specimens may have a pericoel present in the tip of one or more of the lateral extensions. The solid projections are composed of periphragm only which is drawn out beyond the rounded termination of the endophragm. Endophragm smooth or very finely pitted, periphragm finely perforate, and bearing parasutural ridges in some specimens. Perforations are usually about 0.3 µm across but range from 01.0.8 µm. Both walls are very thin, about 0.2 µm each.
Typically paratabulation is lacking, cingulum is indicated by indentation of the lateral horns and faint to distinct transverse lines, and sulcus is not indicated. Some specimens have a ceratioid paratabulation expressed to varying degrees by low parasutural ridges. Fully paratabulate specimens are rare and have an observed paratabulation formula of 4", 6", Sc, 6"", I p, I ""; the sulcus is not divided. In the apical series, paraplate 4" (Taylor-Evitt paraplate A) is rhombic and fails to reach the apex. In the precingular series, I " (2) is reduced in height and the anterior part of 2" (3) extends onto the ventral side and contacts the first apical paraplate ( I u). Also, 3" (4) is not centered on the dorsal midline but is offset to the right. Paraplates 6" (li), 5c (fi), and 6""" (VIu) lie to the right of the sulcus within a defined ventral area which is rarely subdivided; the anterior margin of 6" ( 1 i) is rounded and mid-ventral. There are four cingular paraplates outside the ventral area; lc (au) is left ventral, 2c (b+c) and 3c (d) span the entire dorsal surface and share a mid-dorsal boundary, and 4c (e) is right ventral. The shape of 5c (fi) is not fully known but it has a gently sinuous shape and widens from right to left as it crosses the ventral area. Postcingular paraplate 3""" (IV), instead of being centered on the dorsal midline, is offset to the left; 5""" (VIi) forms not only part of the right lateral horn, but also part of the right antapical horn. 6""" (VIu) lies within the ventral area and is of uncertain shape. The antapical paraplate (Y) is mostly dorsal. The sulcus is narrow, undivided, inclined to the longitudinal axis, and extends almost to the antapical concavity.
The apical horn is composed of three paraplates and often appears to bear a small preapical protrusion at its narrowly blunted tip. Each antapical horn is formed by two paraplates, but in each case the horn tip is formed only from paraplate 1""""(Y), the dorsal component of the horn. The lateral horns are formed from precingular, cingular, and postcingular paraplates. Each pre- and postcingular extension is composed of two paraplates, but the tip is again formed from only the dorsal component paraplate.
Archeopyle apical, operculum adnate ventrally, but often broken away. Archeopyle suture weakly angular to zigzag. In paratabulate forms the suture follows the boundary between apicals 2" (B) and 3" (C) and their subjacent precingulars 2"-5" (3-6), terminating at the triple junctions 1"/2"/2" (lu/B/3) and 3"/4"/5" (C/A/6). There is no archeopyle suture mid-ventrally between apicals 1" (1u) and 4" (A) and their subjacent precingular paraplates; this represents the locus of adnation of the operculum.
Size. Length of complete specimen 88(98)107 µm, 15 measurements; length with operculum broken away 65-79 µm, 5 measurements; width 60(66)76 µm; 20 specimens measured. Approximate lengths of horns: apical 23-30 µm, precingular 1-16 µm, postcingular 2-17 µm, left antapical 15-32 µm, right antapical 10-26 µm; distance between apex of endocyst and apical horn tip 4-8 µm.
Affinities:
Bint, 1986, p.153: Nyktericysta davisii differs from N. pannosa in lacking the granular to spinose ornament of that species. N. arachnion is distinguished from N. davisii by having the periphragm partially separated from the endophragm in a reticulate pattern over the cyst body and also in having cornucavations under the horn tips. Muderongia sp. A and M. sp. B illustrated by May (1979) undoubtedly belong in Nyktericysta and both are quite similar to N. davisii, but further comparison is not possible because descriptions were not given.