Back
Mendicodinium
From Williams et al., 2017:
[Mendicodinium, Morgenroth, 1970, p. 347-348; Emendation: Bucefalo Palliani, 1997a, p. 101, 103
Type species: Mendicodinium reticulatum, Morgenroth, 1970 (pl.9, figs.5–6)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Morgenroth, 1970]: (Translation: Stover and Evitt 1978, p. 214):
Diagnosis:
Dinoflagellate cysts generally without reflected tabulation. Test without apical or antapical horns. Not subdivided into inner body and outer wall. A laevorotatory cingulum and a sulcus may be indicated by slight intrusions into the wall. The archaeopyle is formed by a rupture which starts on the dorsal side immediately above the indicated cingulum on the epitract.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Modified description:
Stover and Evitt, 1978, p. 214:
Synopsis:
Cysts proximate, subspherical; autophragm punctoreticulate to reticulate; essentially without indications of paratabulation; combination archaeopyle Type tAtPa.
Description:
Shape: Subspherical.
Wall relationships: Autophragm only.
Wall features: No parasutural features. Autophragm punctoreticulate to irregularly reticulate.
Paratabulation: Indications vague and essentially lacking, except for paracingulum and parasulcus.
Archaeopyle: Combination, epicystal, Type tAtPa; constituent paraplates not indicated; operculum normally attached ventrally.
Paracingulum: Vaguely indicated by faint transverse equatorial concavity, most clearly visible along the outline.
Parasulcus: Position indicated by ill-defined depression, primarily on the hypocyst.
Size: small.
Affinities:
Mendicodinium differs from Eodinia, which also has a combination epicystal Type tAtPa archaeopyle, in having an autophragm only, rather than an autophragm and ectophragm; it differs from Wanaea in lacking indications of paratabulation and/or a paracingular flange.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Restated description:
Brideaux, 1977, p. 19:
Diagnosis (restated):
Phragma: Autophragm thin, constant thickness; surface sculpture variable and including scabrate, apiculate, and reticulate ornament.
Paratabulation: Evidence for determinable paratabulation lacking, except in the vicinity of the epicystal archeopyle and in the presumed perisulcal region where what is interpreted as an anterior sulcal paraplate is represented.
Archeopyle/operculum: Archeopyle formed by the presumed loss of the apical and precingular paraplate series; operculum simple, commonly free but attached on some specimens along the anterior parasuture of the presumed anterior sulcal paraplate, formed of the apical and precingular paraplate series. Formula AP(?a).
Pericingulum/perisulcus: Pericingulum present or absent; when present, indicated by a slight invagination of the ambitus near the midlatitude of the autocyst. Perisulcus present or absent; when present, position indicated by a medial ventral invagination of the autocyst profile and the presumed anterior sulcal paraplate.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Bucefalo Palliani et al., 1997:
Diagnosis:
Ellipsoidal to subspherical, acavate dinoflagellate cysts, flattened dorso-ventrally.
Size varies from < 50 to 100 µm (small to large of Stover and Evitt, 1978, p. 5).
Typically, species are elongate equatorially, the width being significantly greater than the height. Cysts proximate to proximochorate. Autophragm of variable thickness, smooth, microreticulate, reticulate or ornamented by nontabular positive elements. Typically the ornamentation is of low relief and may comprise microscabrae, scabrae, microgranules, granules, verrucae or short spines.
Paratabulation indicated only by a laevorotatory paracingulum, parasulcus and archeopyle sutures, presumably gonyaulacacean.
Archeopyle epicystal (type tEa), operculum adnate ventrally. Principal archeopyle suture developed immediately anterior of the paracingulum. Accessory archeopyle suture may be developed between Kofoidian paraplates ? 1" and 2".
Discussion:
The original generic diagnosis of Morgenroth (1970), and the modified description of Stover and Evitt (1978) are emended principally to include proximochorate forms (e.g., Mendicodinium spinosum Bucefalo Palliani, Riding et Torricelli, sp. nov.), to fully document the variety of ornamentation types, to stress the significant size variation in this genus and to include minor accessory archeopyle sutures (Fig. 3). Certain acritarchs with apparently equatorial, straight excystment sutures are similar to the species of Mendicodinium described herein. These include Micrhystridium sp. of Guy-Holson and Nordling (1994, pl. 2, fig. 10), which resembles Mendicodinium spinosum Bucefalo Palliani, Riding et Torricelli, sp. nov. Long-ranging acanthomorph acritarchs such as Micrhystridium frequently exhibit no excystment suture or are characterized by small and variable sutures; apparently epicystal sutures are rare. The Mendicodinium species described herein have relatively short stratigraphical ranges and consistently exhibit epicystal archeopyles. Other acritarchs with equatorial or laevorotatory-equatorial excystment sutures were described by Miller and Wood (1982), Le Herisse (1984) and Miller (1987).
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Mendicodinium Morgenroth, 1970, emend. Bucefalo Palliani et al., 1997a. Emended by Bucefalo Palliani et al. (1997a, p.101) as follows, Ellipsoidal to subspherical, acavate dinoflagellate cysts, flattened dorso-ventrally. Size varies from less than 50 to 100 `b5m (small to large of Stover and Evitt, 1978). Typically, species are elongate equatorially, the width being significantly greater than the height. Cysts proximate to proximochorate. Autophragm of variable thickness, smooth, microreticulate, reticulate or ornamented by nontabular positive elements. Typically, the ornamentation is of low relief and may comprise microscabrae, scabrae, microgranules, granules, verrucae or short spines. Paratabulation indicated only by a laevorotatory paracingulum, parasulcus, and archeopyle sutures, presumably gonyaulacacean. Archeopyle epicystal (type tEa), operculum adnate ventrally. Principal archeopyle suture developed immediately anterior of the paracingulum. Accessory archeopyle suture may be developed between Kofoidian paraplates ? 1" and 2".
[Mendicodinium, Morgenroth, 1970, p. 347-348; Emendation: Bucefalo Palliani, 1997a, p. 101, 103
Type species: Mendicodinium reticulatum, Morgenroth, 1970 (pl.9, figs.5–6)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Morgenroth, 1970]: (Translation: Stover and Evitt 1978, p. 214):
Diagnosis:
Dinoflagellate cysts generally without reflected tabulation. Test without apical or antapical horns. Not subdivided into inner body and outer wall. A laevorotatory cingulum and a sulcus may be indicated by slight intrusions into the wall. The archaeopyle is formed by a rupture which starts on the dorsal side immediately above the indicated cingulum on the epitract.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Modified description:
Stover and Evitt, 1978, p. 214:
Synopsis:
Cysts proximate, subspherical; autophragm punctoreticulate to reticulate; essentially without indications of paratabulation; combination archaeopyle Type tAtPa.
Description:
Shape: Subspherical.
Wall relationships: Autophragm only.
Wall features: No parasutural features. Autophragm punctoreticulate to irregularly reticulate.
Paratabulation: Indications vague and essentially lacking, except for paracingulum and parasulcus.
Archaeopyle: Combination, epicystal, Type tAtPa; constituent paraplates not indicated; operculum normally attached ventrally.
Paracingulum: Vaguely indicated by faint transverse equatorial concavity, most clearly visible along the outline.
Parasulcus: Position indicated by ill-defined depression, primarily on the hypocyst.
Size: small.
Affinities:
Mendicodinium differs from Eodinia, which also has a combination epicystal Type tAtPa archaeopyle, in having an autophragm only, rather than an autophragm and ectophragm; it differs from Wanaea in lacking indications of paratabulation and/or a paracingular flange.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Restated description:
Brideaux, 1977, p. 19:
Diagnosis (restated):
Phragma: Autophragm thin, constant thickness; surface sculpture variable and including scabrate, apiculate, and reticulate ornament.
Paratabulation: Evidence for determinable paratabulation lacking, except in the vicinity of the epicystal archeopyle and in the presumed perisulcal region where what is interpreted as an anterior sulcal paraplate is represented.
Archeopyle/operculum: Archeopyle formed by the presumed loss of the apical and precingular paraplate series; operculum simple, commonly free but attached on some specimens along the anterior parasuture of the presumed anterior sulcal paraplate, formed of the apical and precingular paraplate series. Formula AP(?a).
Pericingulum/perisulcus: Pericingulum present or absent; when present, indicated by a slight invagination of the ambitus near the midlatitude of the autocyst. Perisulcus present or absent; when present, position indicated by a medial ventral invagination of the autocyst profile and the presumed anterior sulcal paraplate.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Bucefalo Palliani et al., 1997:
Diagnosis:
Ellipsoidal to subspherical, acavate dinoflagellate cysts, flattened dorso-ventrally.
Size varies from < 50 to 100 µm (small to large of Stover and Evitt, 1978, p. 5).
Typically, species are elongate equatorially, the width being significantly greater than the height. Cysts proximate to proximochorate. Autophragm of variable thickness, smooth, microreticulate, reticulate or ornamented by nontabular positive elements. Typically the ornamentation is of low relief and may comprise microscabrae, scabrae, microgranules, granules, verrucae or short spines.
Paratabulation indicated only by a laevorotatory paracingulum, parasulcus and archeopyle sutures, presumably gonyaulacacean.
Archeopyle epicystal (type tEa), operculum adnate ventrally. Principal archeopyle suture developed immediately anterior of the paracingulum. Accessory archeopyle suture may be developed between Kofoidian paraplates ? 1" and 2".
Discussion:
The original generic diagnosis of Morgenroth (1970), and the modified description of Stover and Evitt (1978) are emended principally to include proximochorate forms (e.g., Mendicodinium spinosum Bucefalo Palliani, Riding et Torricelli, sp. nov.), to fully document the variety of ornamentation types, to stress the significant size variation in this genus and to include minor accessory archeopyle sutures (Fig. 3). Certain acritarchs with apparently equatorial, straight excystment sutures are similar to the species of Mendicodinium described herein. These include Micrhystridium sp. of Guy-Holson and Nordling (1994, pl. 2, fig. 10), which resembles Mendicodinium spinosum Bucefalo Palliani, Riding et Torricelli, sp. nov. Long-ranging acanthomorph acritarchs such as Micrhystridium frequently exhibit no excystment suture or are characterized by small and variable sutures; apparently epicystal sutures are rare. The Mendicodinium species described herein have relatively short stratigraphical ranges and consistently exhibit epicystal archeopyles. Other acritarchs with equatorial or laevorotatory-equatorial excystment sutures were described by Miller and Wood (1982), Le Herisse (1984) and Miller (1987).
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Mendicodinium Morgenroth, 1970, emend. Bucefalo Palliani et al., 1997a. Emended by Bucefalo Palliani et al. (1997a, p.101) as follows, Ellipsoidal to subspherical, acavate dinoflagellate cysts, flattened dorso-ventrally. Size varies from less than 50 to 100 `b5m (small to large of Stover and Evitt, 1978). Typically, species are elongate equatorially, the width being significantly greater than the height. Cysts proximate to proximochorate. Autophragm of variable thickness, smooth, microreticulate, reticulate or ornamented by nontabular positive elements. Typically, the ornamentation is of low relief and may comprise microscabrae, scabrae, microgranules, granules, verrucae or short spines. Paratabulation indicated only by a laevorotatory paracingulum, parasulcus, and archeopyle sutures, presumably gonyaulacacean. Archeopyle epicystal (type tEa), operculum adnate ventrally. Principal archeopyle suture developed immediately anterior of the paracingulum. Accessory archeopyle suture may be developed between Kofoidian paraplates ? 1" and 2".