Back
Mikrocysta erugata
Mikrocysta erugata Bjaerke, 1980; emend. Below, 1987
Holotype: Bjaerke, 1980, pl.5, fig.10
Locus typicus: Knorringfjellet, Spitsbergen
Stratum typicum: Toarcian
Translation Below, 1987: Fensome et al., 1993
Original diagnosis: Bjaerke, 1980, p.71
Dinoflagellate cysts of the genus Mikrocysta with a semispherical epicyst and an almost semispherical hypocyst with two lateral inflations. Cyst slightly dorso-ventrally flattened. Epicyst distinctly smaller than hypocyst separated by a distinct wide paracingular depression. Cyst surface smooth.
Original description: Bjaerke, 1980, p.72
Small dinoflagellate cysts with a semispherical epicyst and a nearly semispherical hypocyst modified by two inflations in lateral positions. Cyst slightly dorso-ventrally flattened. Epicyst smaller than hypocyst, separated by a depression representing paracingulum. Faint parasutures observed along paracingulum in some specimens. Cyst wall single layered, smooth Archeopyle formed by the loss of apical and intercalary paraplates, number and outline not known In some specimens only one intercalary paraplate seems to be missing indicating that archeopyle formation occurs in steps starting with one of the intercalary paraplates. Paratabulation otherwise not observed. Paracingulum represented by the depression separating epicyst and hypocyst. Parasulcus indicated by a depression running from the paracingular depression towards antapex.
Emended description: Below, 1987, p.16-17
Arrangement of vesicles/plates on the dinoflagellate amphiesma PR, 5", 3a-4a, 7", 7c, 6""", 2"""", as, FM with numerous peliflagellar platelets, ls, rs, ps; pentagonal 1"""" and hexagonal 2"""" partiform; omegaform ps very large. Cyst form proximate, acavate to holocavate, cruciform, seldom ovaloidal, epicyst of distinctly lesser length and breadth than the hypocyst and separated from it by a broad, deeply indented cingulum, epicyst transversely ellipsoidal, hypocyst transversely ellipsoidal and usually protuberant at the sites of areae, but especially laterally and antapically, cross-section lenticular to oval, seldom circular, maximum diameter at the posterior margin of the cingulum; size small; wall composed of pedium and superposed spongy luxuria, luxuria also separated from the pedium as a tectum by a low pericoel, surface glabrous, scabrate, finely rugulate or vermiculate and occasionally with very fine, finate crests, seldom limbate, nonareate, partially or completely areate; areation formula NR PR/PR, NR"/5", 1a, NR2a/2a, 3a, 4a, 7", 7c, 6""", 2""", as, FM, ls, rs, ps; PR not reflected or undifferentiated, 5 minute apical areae usually rudimentary, VI 1" (V), inverse-camerate 2" (VL), V 3" (L), V 4" (R), inverse-camerate 5" (VR); 4 anterior intercalaries, VI 1a (DL), very small trigonal 2a (DL) often not reflected, VIII 3a (D), VI 4a (R); 7 precingulars, anteriorly geniculate V-nE 1" (VL), anteriorly geniculate V-nE 2" (L), anteriorly geniculate or bigeniculate V-nE or VI-nE 3" (DL), anteriorly linear IV-nE 4" (D), anteriorly geniculate V-nE 5" (DR), anteriorly geniculate V-nE 6" (RVR), anteriorly geniculate V-nE 7" (VVR); cingulum weakly helicoid laevorotatory, broad, deeply indented, almost always with striking, sharpedged anterior and posterior margins, heptaareate, lati 1c to 6c, fastigiate 7c (VVL); 6 postcingulars, posteriorly linear V-nE 1""" (VVL), posteriorly linear IV-nE 2""" (VL), posteriorly geniculate V-nE 3""" (DL), posteriorly linear IV-nE 4""" (D), posteriorly linear IV-nE 5""" (RDR), posteriorly linear V-nE 6""" (VVR); 2 antapicals partiform, V 1"""" (VL) and VI 2"""" sloping down towards D to R; sulcus shallowly indented, quasideltaform-linteloid as, FM a longitudinally oval pit, small IV-nE Is and small IV-nE rs, large omegaform VI ps; archeopyle apical, amplificate, 3" + 4"; operculum solvate, secate, general opercular formula 3"[s] + 4"[s].
Range: length 25-28 Ám, width 20-28 Ám.
Additional remarks: Below, 1987, p.17 (annotated translation in Fensome et al., 1993, p.1148)
Even under the SEM, details of the rarely fully expressed areation are barely discernible on this very small cyst. This applies especially to the apex. Only [one] specimen ([Below, 1987b] pl 1, fig 1), with the operculum still in situ, reveals very fine, finate rows of punctules suggesting that there is only one area (in this case, 3") on the dorsal side of 1". However, this is not consistent with the formation of the archeopyle in this region. It breaks up into two opercular pieces corresponding to areae 3" and 4". The archeopyle is frequently amplificate, since the anterior portions of 4a and 1" and especially 2" and 5" are integrated into the two opercular pieces, and because of its very rounded margins, the archeopyle is nearly circular. On other specimens, archeopyle sutures follow the fines exactly 3a and 5" are anteriorly geniculate or linear. Although the boundaries of these two areae are met respectively by finis 3"/4" and finis 3a/4a, so that there should be geniculate anterior boundaries at these triple junctures, [areae 3a and 5"] often [areae 3a and 5"] have linear anterior boundaries.
The small triangular area 2a is rarely discernible It is strikingly reminiscent of the similarily small, triangular anterior intercalary area in Dapcodinium ovale ....
Thecal-plate growth could be detected only on [one] specimen ([Below, 1987b] pl 1, figs 8-10,15) The original thecal plate is reflected by a somewhat raised intraareate region, around which transversely striate limbi (reflecting intercalary striae) are grouped. The postcingulars have broad limbi along their boundaries facing the cingular areae, which do not have limbi; this signifies that the postcingulars overlapped the cingulum. On the other side, the intraareate surfaces of the precingular areae abut the cingular intraareate surfaces directly along the anterior margin of the cingulum, or else the intraareate surfaces of the two series are separated only by very narrow limbi. Therefore the precingular and cingular thecal plates met without any overlap or any noticeable incremental zone.
Holotype: Bjaerke, 1980, pl.5, fig.10
Locus typicus: Knorringfjellet, Spitsbergen
Stratum typicum: Toarcian
Translation Below, 1987: Fensome et al., 1993
Original diagnosis: Bjaerke, 1980, p.71
Dinoflagellate cysts of the genus Mikrocysta with a semispherical epicyst and an almost semispherical hypocyst with two lateral inflations. Cyst slightly dorso-ventrally flattened. Epicyst distinctly smaller than hypocyst separated by a distinct wide paracingular depression. Cyst surface smooth.
Original description: Bjaerke, 1980, p.72
Small dinoflagellate cysts with a semispherical epicyst and a nearly semispherical hypocyst modified by two inflations in lateral positions. Cyst slightly dorso-ventrally flattened. Epicyst smaller than hypocyst, separated by a depression representing paracingulum. Faint parasutures observed along paracingulum in some specimens. Cyst wall single layered, smooth Archeopyle formed by the loss of apical and intercalary paraplates, number and outline not known In some specimens only one intercalary paraplate seems to be missing indicating that archeopyle formation occurs in steps starting with one of the intercalary paraplates. Paratabulation otherwise not observed. Paracingulum represented by the depression separating epicyst and hypocyst. Parasulcus indicated by a depression running from the paracingular depression towards antapex.
Emended description: Below, 1987, p.16-17
Arrangement of vesicles/plates on the dinoflagellate amphiesma PR, 5", 3a-4a, 7", 7c, 6""", 2"""", as, FM with numerous peliflagellar platelets, ls, rs, ps; pentagonal 1"""" and hexagonal 2"""" partiform; omegaform ps very large. Cyst form proximate, acavate to holocavate, cruciform, seldom ovaloidal, epicyst of distinctly lesser length and breadth than the hypocyst and separated from it by a broad, deeply indented cingulum, epicyst transversely ellipsoidal, hypocyst transversely ellipsoidal and usually protuberant at the sites of areae, but especially laterally and antapically, cross-section lenticular to oval, seldom circular, maximum diameter at the posterior margin of the cingulum; size small; wall composed of pedium and superposed spongy luxuria, luxuria also separated from the pedium as a tectum by a low pericoel, surface glabrous, scabrate, finely rugulate or vermiculate and occasionally with very fine, finate crests, seldom limbate, nonareate, partially or completely areate; areation formula NR PR/PR, NR"/5", 1a, NR2a/2a, 3a, 4a, 7", 7c, 6""", 2""", as, FM, ls, rs, ps; PR not reflected or undifferentiated, 5 minute apical areae usually rudimentary, VI 1" (V), inverse-camerate 2" (VL), V 3" (L), V 4" (R), inverse-camerate 5" (VR); 4 anterior intercalaries, VI 1a (DL), very small trigonal 2a (DL) often not reflected, VIII 3a (D), VI 4a (R); 7 precingulars, anteriorly geniculate V-nE 1" (VL), anteriorly geniculate V-nE 2" (L), anteriorly geniculate or bigeniculate V-nE or VI-nE 3" (DL), anteriorly linear IV-nE 4" (D), anteriorly geniculate V-nE 5" (DR), anteriorly geniculate V-nE 6" (RVR), anteriorly geniculate V-nE 7" (VVR); cingulum weakly helicoid laevorotatory, broad, deeply indented, almost always with striking, sharpedged anterior and posterior margins, heptaareate, lati 1c to 6c, fastigiate 7c (VVL); 6 postcingulars, posteriorly linear V-nE 1""" (VVL), posteriorly linear IV-nE 2""" (VL), posteriorly geniculate V-nE 3""" (DL), posteriorly linear IV-nE 4""" (D), posteriorly linear IV-nE 5""" (RDR), posteriorly linear V-nE 6""" (VVR); 2 antapicals partiform, V 1"""" (VL) and VI 2"""" sloping down towards D to R; sulcus shallowly indented, quasideltaform-linteloid as, FM a longitudinally oval pit, small IV-nE Is and small IV-nE rs, large omegaform VI ps; archeopyle apical, amplificate, 3" + 4"; operculum solvate, secate, general opercular formula 3"[s] + 4"[s].
Range: length 25-28 Ám, width 20-28 Ám.
Additional remarks: Below, 1987, p.17 (annotated translation in Fensome et al., 1993, p.1148)
Even under the SEM, details of the rarely fully expressed areation are barely discernible on this very small cyst. This applies especially to the apex. Only [one] specimen ([Below, 1987b] pl 1, fig 1), with the operculum still in situ, reveals very fine, finate rows of punctules suggesting that there is only one area (in this case, 3") on the dorsal side of 1". However, this is not consistent with the formation of the archeopyle in this region. It breaks up into two opercular pieces corresponding to areae 3" and 4". The archeopyle is frequently amplificate, since the anterior portions of 4a and 1" and especially 2" and 5" are integrated into the two opercular pieces, and because of its very rounded margins, the archeopyle is nearly circular. On other specimens, archeopyle sutures follow the fines exactly 3a and 5" are anteriorly geniculate or linear. Although the boundaries of these two areae are met respectively by finis 3"/4" and finis 3a/4a, so that there should be geniculate anterior boundaries at these triple junctures, [areae 3a and 5"] often [areae 3a and 5"] have linear anterior boundaries.
The small triangular area 2a is rarely discernible It is strikingly reminiscent of the similarily small, triangular anterior intercalary area in Dapcodinium ovale ....
Thecal-plate growth could be detected only on [one] specimen ([Below, 1987b] pl 1, figs 8-10,15) The original thecal plate is reflected by a somewhat raised intraareate region, around which transversely striate limbi (reflecting intercalary striae) are grouped. The postcingulars have broad limbi along their boundaries facing the cingular areae, which do not have limbi; this signifies that the postcingulars overlapped the cingulum. On the other side, the intraareate surfaces of the precingular areae abut the cingular intraareate surfaces directly along the anterior margin of the cingulum, or else the intraareate surfaces of the two series are separated only by very narrow limbi. Therefore the precingular and cingular thecal plates met without any overlap or any noticeable incremental zone.