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Stephanelytron membranoideum
Stephanelytron membranoideum (Vozzhennikova, 1967, p.114–115, pl.48, figs.1–2,3a–b,4a–b,5–8,9a–c,10) Courtinat, 1999, p.178. Emendation: Lentin and Vozzhennikova, 1990, p.103, as Lagenadinium? membranoideum.
Originally Chlamydophorella, subsequently Chlamydophorella?, thirdly Lagenadinium?, fourthly (and now) Stephanelytron.
Taxonomic junior synonym: Stephanelytron cretaceum, according to Heilmann-Clausen in Heilmann-Clausen and Thomsen (1995, p.301) — however, Courtinat (1999, p.178) retained Stephanelytron cretaceum.
Holotype: Vozzhennikova, 1967, pl.48, figs.9a–b; Lentin and Vozzhennikova, 1990, text-fig.58; lost according to Lentin and Vozzhennikova (1990, p.103).
Lectotype: ?Vozzhennikova, 1967, pl.48, fig.6; Lentin and Vozzhennikova, 1990, pl.10, figs.6–7; designated by Lentin and Vozzhennikova (1990, p.103).
Age: Late Jurassic.
Original description: Vozzhennikova, 1967, p.114-115: Chlamydophorella membranoidea
Theca with an oval-polygonal outline, densely covered with short processes which bifurcate at the distal end and which fuse together near the bifurcations thus forming a second polygonal, wavy membrane to the theca. It appears as though the processes are supporting this membrane. The fields, transverse furrow and pylome (of oval or triangular shape) are all bounded by rows of outgrowths the bifurcating ends of which join together. Over the rest of the theca the outgrowths are arranged regularly. The number of fields has not been determined.
Emended description: Lentin and Vozzhennikova, 1990, p.103
Cyst shape subspherical without an apical horn holocavate autophragm with numerous hollow, thin, intratabular processes supporting a delicate ectophragm; ectophragm thin and smooth. Paratabulation incompletely indicated by intratabular distribution of autophragmal processes and distinct to indistinct ridges on the ectophragm; gonyaulacoid Archeopyle formed by the loss of all apical paraplates, but operculum often remaining in place; accessory sutures commonly present in precingular series of paraplates. Hypocystal corona present on ectophragm approximately over the location of the 2""" paraplate. Paracingulum inticated by alignment of autophragmal processes and two parallel ridges on the ectophragm; parasulcus indistinct.
Size: Holotype, length 46 µm, width 43 µm, length of processes 5-6 µm. Lectotype, length 47 µm, width 51 µm.
Affinities:
Vozzhennikova, 1967, p. 115: C. membranoidea differs from other species of the genus in having an oval- polygonal outline to the theca, in the absence of any apical processes and the presence of fields and a transverse furrow.
Lentin and Vozzhennikova, 1990, p.104: The degree of intratabular distribution of the autophragmal processes in this species is highly variable. Some specimens exhibit no indication of paratabulation, others have distinctly intratabular distribution of the processes and strong sutural ridges on the ectophragm. At least 40 specimens of this species were observed with a continuous series of morphologies. Davey (1982) reported a high degree of variability in the expression of the paratabulation in his specimens of this species recovered from Denmark. The hypocystal corona is present on all specimens examined and appears to reflect the shape of the 2""" paraplate (see Pl. 10, fig.8-9 and 11), and not the antapical paraplate which is displaced onto the dorsal surface as suggested by Davey, 1982. In the type species of the genus Lagenadinium, L. callovianum, the corona (or coronas, if two are present) is usual approximately circular in outline and smaller than the underlying paraplate would be.
Originally Chlamydophorella, subsequently Chlamydophorella?, thirdly Lagenadinium?, fourthly (and now) Stephanelytron.
Taxonomic junior synonym: Stephanelytron cretaceum, according to Heilmann-Clausen in Heilmann-Clausen and Thomsen (1995, p.301) — however, Courtinat (1999, p.178) retained Stephanelytron cretaceum.
Holotype: Vozzhennikova, 1967, pl.48, figs.9a–b; Lentin and Vozzhennikova, 1990, text-fig.58; lost according to Lentin and Vozzhennikova (1990, p.103).
Lectotype: ?Vozzhennikova, 1967, pl.48, fig.6; Lentin and Vozzhennikova, 1990, pl.10, figs.6–7; designated by Lentin and Vozzhennikova (1990, p.103).
Age: Late Jurassic.
Original description: Vozzhennikova, 1967, p.114-115: Chlamydophorella membranoidea
Theca with an oval-polygonal outline, densely covered with short processes which bifurcate at the distal end and which fuse together near the bifurcations thus forming a second polygonal, wavy membrane to the theca. It appears as though the processes are supporting this membrane. The fields, transverse furrow and pylome (of oval or triangular shape) are all bounded by rows of outgrowths the bifurcating ends of which join together. Over the rest of the theca the outgrowths are arranged regularly. The number of fields has not been determined.
Emended description: Lentin and Vozzhennikova, 1990, p.103
Cyst shape subspherical without an apical horn holocavate autophragm with numerous hollow, thin, intratabular processes supporting a delicate ectophragm; ectophragm thin and smooth. Paratabulation incompletely indicated by intratabular distribution of autophragmal processes and distinct to indistinct ridges on the ectophragm; gonyaulacoid Archeopyle formed by the loss of all apical paraplates, but operculum often remaining in place; accessory sutures commonly present in precingular series of paraplates. Hypocystal corona present on ectophragm approximately over the location of the 2""" paraplate. Paracingulum inticated by alignment of autophragmal processes and two parallel ridges on the ectophragm; parasulcus indistinct.
Size: Holotype, length 46 µm, width 43 µm, length of processes 5-6 µm. Lectotype, length 47 µm, width 51 µm.
Affinities:
Vozzhennikova, 1967, p. 115: C. membranoidea differs from other species of the genus in having an oval- polygonal outline to the theca, in the absence of any apical processes and the presence of fields and a transverse furrow.
Lentin and Vozzhennikova, 1990, p.104: The degree of intratabular distribution of the autophragmal processes in this species is highly variable. Some specimens exhibit no indication of paratabulation, others have distinctly intratabular distribution of the processes and strong sutural ridges on the ectophragm. At least 40 specimens of this species were observed with a continuous series of morphologies. Davey (1982) reported a high degree of variability in the expression of the paratabulation in his specimens of this species recovered from Denmark. The hypocystal corona is present on all specimens examined and appears to reflect the shape of the 2""" paraplate (see Pl. 10, fig.8-9 and 11), and not the antapical paraplate which is displaced onto the dorsal surface as suggested by Davey, 1982. In the type species of the genus Lagenadinium, L. callovianum, the corona (or coronas, if two are present) is usual approximately circular in outline and smaller than the underlying paraplate would be.