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Microdinium
From Williams et al., 2017:
[Microdinium, Cookson and Eisenack, 1960a, p. 6; Emendations: Sarjeant, 1966b, p.148–149; Stover and Evitt, 1978, p.65–66; Slimani, 1994, p.24.
Cyst type Gp Microdinium p.p., including M. ornatum and M. veligerum; Cyst type Gp Phanerodinium p.p., including M. opacum and M. spinosum
Tax. jr. syn. of Phanerodinium Deflandre, 1937, according to Below, 1987. Lentin and Williams, 1989, retained Microdinium as a separate genus.
Tax. sr. synonym of Fibradinium Morgenroth, 1968, Rhiptocorys Lejeune-Carpentier and Sarjeant, 1983, and Subtilidinium Morgenroth, 1968, according to Below, 1987. Lentin and Williams, 1989, retained them as separate genera.
Type species: Microdinium ornatum, Cookson and Eisenack, 1960a (pl.2, figs.3–4; text-fig.2)]
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Original description: [Cookson and Eisenack, 1960]: ( Translation: LPP):
Description:
Shell small, more or less oval in outline, with a circular girdle level with the surface, and without appendages; epitheca with one apical plate and 6 pre-equatorial plates; hypotheca with 6 postequatorial plates, plate lp, and one antapical plate. The longitudinal furrow, which is level with the surface, broadens towards both apex and antapex; a few small plates may be associated with it on the epitheca. The shell opens by the detachment of the apical plate.
Affinities:
Microdinium resembles the genus Eisenackia Deflandre and Cookson, 1955, but differs from it in having only one apical plate instead of two or three, and in the broadening of the longitudinal furrow towards both apex and antapex. Furthermore, the small plates associated with the longitudinal furrow are situated in the epitheca in Microdinium and not in the hypotheca, as in Eisenackia.
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Emended description:
Sarjeant, 1966:
Description:
Proximate dinoflagellate cysts, spheroidal to ovoidal in shape and usually small. Epitract smaller than hypotract.
Tabulation 1`, O-?la, 6", 6c, 6```, lp, 1````, with differentiation in some species of additional plates in ventral region.
Cingulum broad, weakly spiral; sulcus broad, extending from apex to antapex. Sutures bearing crests in form of low ridges (perforate or imperforate), smooth, denticulate or bearing spines of varying lengths; alternatively sutures marked by lines of closely set spines. Shell surface smooth, granular, punctate or tuberculate. Archeopyle formation by loss of single apical plate.
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Stover and Evitt, 1978:
Synopsis:
Cysts proximate, subspherical to elongate ellipsoidal; epicyst typically shorter than hypocyst; paratabulation indicated by parasutural ridges, formula: 1-4`, 0-3a, 6-7", 6c, 5-6```, lp, 1````, 0-5s; archeopyle apical, Type (tA) only, or may include intercalary paraplates (tAtl).
Description:
Shape: Subspherical to elongate ellipsoidal.
Wall relationships: Autophragm only.
Wall features: Parasutural ridges low, occasionally perforate; crests smooth, denticulate, or bearing spines of different lengths. Autophragm smooth or variously ornamented with features of low relief.
Paratabulation: Indicated by parasutural features, formula: 1-4`, 0-3a, 6", 6c, 5-6```, lp, 1````, 0-5s.
Archeopyle: Apical, Type (tA) only or Type (tAtl) when intercalary paraplates are included; operculum normally free, but may be adherent.
Paracingulum: Indicated by six transversely elongate, rectangular paraplates; paracingulum divides cyst into unequal parts; epicyst shorter than hypocyst.
Parasulcus: Longitudinally elongate area, generally subdivided with one to four small paraplates near the paracingulum and a larger paraplate on the hypocyst; antapical end normally wider than apical end.
Size: Small.
Affinities:
Microdinium differs from Druggidium in having an apical rather than a precingular archeopyle. The paratabulation of Microdinium and Cladopyxidium is possibly the same; however, the archeopyle in Microdinium involves all of the apical paraplates and may involve anterior intercalary paraplates as well. In Cladopyxidium the archeopyle is formed by the release of only two apical paraplates. Fibradinium has a fibrous autophragm, whereas in Microdinium it is smooth or ornamented with features of low relief.
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Slimani, 1994, p. 24:
Diagnosis:
Cysts proximate, proximochorate, acavate to cavate, spheroidal, ovoidal to ellipsoidal or polyhedrical; mostly, the epicyst is slightly smaller than the hypocyst. The cyst wall is composed of a smooth or ornamented endophragm and periphragm. The paratabulation is partiform gonyaulacoid and corresponds to the following formula: 4`, 4a, 6-7``, 6c-7c, 6-7```, 1-5s; the posterior sulcal paraplate is the largest and often omegaform. This paratabulation is indicated by parasutural reliefs which are mostly expressed by solid or hollow, smooth or distally denticulate, spinous or crusty to clotty crets; or also by unornamented parasutural furrows. The archaeopyle is apical-intercalary type (tAtI)a with a ventrally adnate operculum, mostly on (paraplate) as; the operculum is generally composed of 9 small paraplate, 1 pre-apical, 4 apicals and 4 anterior intercalaries.
Affinities:
Microdinium and Rhiptocorys Lejeune-Carpentier and Sarjeant, 1983 emend. Slimani, 1994, are very similar, but they differ in the fact that in Rhiptocorys the epicyst is extremely much smaller than the hypocyst and lacks clear parasutural reliefs. Phanerodinium Deflandre, 1937 emend. Slimani, 1994, and Druggidinium Habib, 1973 emend. Harding, 1986, have a precingular archaeopyle. Membranigonyaulax Slimani, 1994, is larger and presents an ectophragm covering the parasutural and intratabular relief, and has a type (4A) archaeopyle with a deep sulcal notch and a generally free operculum.
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Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
d\tx-1262\tx-720\tx9360\tx10080\tx10800\tx11520 Microdinium Cookson and Eisenack, 1960a, emend. Stover and Evitt, 1978, emend. Slimani, 1994. As emended by Slimani (1994, p.24). Cyst proximate, proximochorate, acavate to cavate, spheroidal, ovoidal to ellipsoidal or polyhedral; in most cases the epicyst is smaller than the hypocyst. The cyst wall is composed of endophragm and smooth to ornamented periphragm. The paratabulation is gonyaulacacean partiform and corresponds to the formula 4`, 4a, 6-7", 6c-7c, 6-7"', 1p, 1-5s, 1"''. The posterior sulcal paraplate is large and often omegaform. This paratabulation is indicated by parasutural features which are expressed most often by crests that are solid or hollow, perforated, smooth or distally denticulate, spinose or granulose to verrucate; or by parasutural grooves devoid of ornamentation. The archeopyle is apical-intercalary of the type (tAtI)a with an adnate operculum ventrally most commonly attached to the as; the operculum is composed generally of nine small paraplates of which there is 1 preapical, 4 apicals and 4 anterior intercalaries.
[Microdinium, Cookson and Eisenack, 1960a, p. 6; Emendations: Sarjeant, 1966b, p.148–149; Stover and Evitt, 1978, p.65–66; Slimani, 1994, p.24.
Cyst type Gp Microdinium p.p., including M. ornatum and M. veligerum; Cyst type Gp Phanerodinium p.p., including M. opacum and M. spinosum
Tax. jr. syn. of Phanerodinium Deflandre, 1937, according to Below, 1987. Lentin and Williams, 1989, retained Microdinium as a separate genus.
Tax. sr. synonym of Fibradinium Morgenroth, 1968, Rhiptocorys Lejeune-Carpentier and Sarjeant, 1983, and Subtilidinium Morgenroth, 1968, according to Below, 1987. Lentin and Williams, 1989, retained them as separate genera.
Type species: Microdinium ornatum, Cookson and Eisenack, 1960a (pl.2, figs.3–4; text-fig.2)]
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Original description: [Cookson and Eisenack, 1960]: ( Translation: LPP):
Description:
Shell small, more or less oval in outline, with a circular girdle level with the surface, and without appendages; epitheca with one apical plate and 6 pre-equatorial plates; hypotheca with 6 postequatorial plates, plate lp, and one antapical plate. The longitudinal furrow, which is level with the surface, broadens towards both apex and antapex; a few small plates may be associated with it on the epitheca. The shell opens by the detachment of the apical plate.
Affinities:
Microdinium resembles the genus Eisenackia Deflandre and Cookson, 1955, but differs from it in having only one apical plate instead of two or three, and in the broadening of the longitudinal furrow towards both apex and antapex. Furthermore, the small plates associated with the longitudinal furrow are situated in the epitheca in Microdinium and not in the hypotheca, as in Eisenackia.
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Emended description:
Sarjeant, 1966:
Description:
Proximate dinoflagellate cysts, spheroidal to ovoidal in shape and usually small. Epitract smaller than hypotract.
Tabulation 1`, O-?la, 6", 6c, 6```, lp, 1````, with differentiation in some species of additional plates in ventral region.
Cingulum broad, weakly spiral; sulcus broad, extending from apex to antapex. Sutures bearing crests in form of low ridges (perforate or imperforate), smooth, denticulate or bearing spines of varying lengths; alternatively sutures marked by lines of closely set spines. Shell surface smooth, granular, punctate or tuberculate. Archeopyle formation by loss of single apical plate.
---------------------------------------------
Stover and Evitt, 1978:
Synopsis:
Cysts proximate, subspherical to elongate ellipsoidal; epicyst typically shorter than hypocyst; paratabulation indicated by parasutural ridges, formula: 1-4`, 0-3a, 6-7", 6c, 5-6```, lp, 1````, 0-5s; archeopyle apical, Type (tA) only, or may include intercalary paraplates (tAtl).
Description:
Shape: Subspherical to elongate ellipsoidal.
Wall relationships: Autophragm only.
Wall features: Parasutural ridges low, occasionally perforate; crests smooth, denticulate, or bearing spines of different lengths. Autophragm smooth or variously ornamented with features of low relief.
Paratabulation: Indicated by parasutural features, formula: 1-4`, 0-3a, 6", 6c, 5-6```, lp, 1````, 0-5s.
Archeopyle: Apical, Type (tA) only or Type (tAtl) when intercalary paraplates are included; operculum normally free, but may be adherent.
Paracingulum: Indicated by six transversely elongate, rectangular paraplates; paracingulum divides cyst into unequal parts; epicyst shorter than hypocyst.
Parasulcus: Longitudinally elongate area, generally subdivided with one to four small paraplates near the paracingulum and a larger paraplate on the hypocyst; antapical end normally wider than apical end.
Size: Small.
Affinities:
Microdinium differs from Druggidium in having an apical rather than a precingular archeopyle. The paratabulation of Microdinium and Cladopyxidium is possibly the same; however, the archeopyle in Microdinium involves all of the apical paraplates and may involve anterior intercalary paraplates as well. In Cladopyxidium the archeopyle is formed by the release of only two apical paraplates. Fibradinium has a fibrous autophragm, whereas in Microdinium it is smooth or ornamented with features of low relief.
---------------------------------------------
Slimani, 1994, p. 24:
Diagnosis:
Cysts proximate, proximochorate, acavate to cavate, spheroidal, ovoidal to ellipsoidal or polyhedrical; mostly, the epicyst is slightly smaller than the hypocyst. The cyst wall is composed of a smooth or ornamented endophragm and periphragm. The paratabulation is partiform gonyaulacoid and corresponds to the following formula: 4`, 4a, 6-7``, 6c-7c, 6-7```, 1-5s; the posterior sulcal paraplate is the largest and often omegaform. This paratabulation is indicated by parasutural reliefs which are mostly expressed by solid or hollow, smooth or distally denticulate, spinous or crusty to clotty crets; or also by unornamented parasutural furrows. The archaeopyle is apical-intercalary type (tAtI)a with a ventrally adnate operculum, mostly on (paraplate) as; the operculum is generally composed of 9 small paraplate, 1 pre-apical, 4 apicals and 4 anterior intercalaries.
Affinities:
Microdinium and Rhiptocorys Lejeune-Carpentier and Sarjeant, 1983 emend. Slimani, 1994, are very similar, but they differ in the fact that in Rhiptocorys the epicyst is extremely much smaller than the hypocyst and lacks clear parasutural reliefs. Phanerodinium Deflandre, 1937 emend. Slimani, 1994, and Druggidinium Habib, 1973 emend. Harding, 1986, have a precingular archaeopyle. Membranigonyaulax Slimani, 1994, is larger and presents an ectophragm covering the parasutural and intratabular relief, and has a type (4A) archaeopyle with a deep sulcal notch and a generally free operculum.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
d\tx-1262\tx-720\tx9360\tx10080\tx10800\tx11520 Microdinium Cookson and Eisenack, 1960a, emend. Stover and Evitt, 1978, emend. Slimani, 1994. As emended by Slimani (1994, p.24). Cyst proximate, proximochorate, acavate to cavate, spheroidal, ovoidal to ellipsoidal or polyhedral; in most cases the epicyst is smaller than the hypocyst. The cyst wall is composed of endophragm and smooth to ornamented periphragm. The paratabulation is gonyaulacacean partiform and corresponds to the formula 4`, 4a, 6-7", 6c-7c, 6-7"', 1p, 1-5s, 1"''. The posterior sulcal paraplate is large and often omegaform. This paratabulation is indicated by parasutural features which are expressed most often by crests that are solid or hollow, perforated, smooth or distally denticulate, spinose or granulose to verrucate; or by parasutural grooves devoid of ornamentation. The archeopyle is apical-intercalary of the type (tAtI)a with an adnate operculum ventrally most commonly attached to the as; the operculum is composed generally of nine small paraplates of which there is 1 preapical, 4 apicals and 4 anterior intercalaries.