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Paraevansia brachythelis
Paraevansia brachythelis (Fensome, 1979, p.29–31, pl.4, figs.3,5–7; text-figs.11A–E) Below, 1990, p.58. Emendation: Below, 1990, p.58, as Paraevansia brachythelis.
Originally Pareodinia, subsequently (and now) Paraevansia.
Holotype: Fensome, 1979, pl.4, fig.5; text-fig.11E
Paratype: Fensome, 1979
Locus typicus: Fossilbjerget, Jameson Land, E Greenland
Stratum typicum: Bajocian-Callovian
Translation Below, 1990: LPP
Original description: Fensome 1979, p.29-30: Pareodinia brachythelis.
Diagnosis: A species of Pareodinia having a thick cyst wall densely ornamented by coarse granules or verrucae. The cyst is ovoidal with a smoothly rounded outline, and surmounted by a distinct, short mamelon-like apical horn which is often itself surmounted by a rod-like or irregularly shaped solid apicular structure; similar structures may occur elsewhere on he cyst wall, notably at the antapex. The archaeopyle is intercalary, involving the loss of three (occasionally possibly four or more) paraplates. The operculum is compound. The paracingulum is usually only weakly indicated or absent. There is no other indication of a paratabulation.
Dimensions length breadth apical horn apicular struct.
holotype 52 µm 37 µm 5 µm 2 µm
paratype 54 µm 32 µm 4 µm 2 µm
range 45(54)66 µm 31(36)42 µm 3(6)8 µm 2(3.5)5 µm
(36 spcm.)
Description:
The apical horn is of characteristic shape, with a broad base and a usually well rounded distal extremity (exclusive of any apicular structure). The horn is usually distinct from the rest of the cyst; it is variable in length but, in the type material, this does not exceed one sixth of the overall length of the cyst. Rarely the horn may be very short; indeed one specimen superficially resembles a form of Chytoeisphaeridia. The presence of a rod-like or irregularly shaped apicular structure at the distal tip of the apical horn often gives the apex a more pointed or irregular shape. Solid protruberances of irregular outline may rarely occur elsewhere on the cyst surface, especially at the antapex.
The paratype appears to possess a pre-apical paraplate on its apical horn differentiated from the rest of the cyst by a more lightly stained portion of the cyst wall; this is ornamented by a scatter of coarse, wart-like verrucae. A pre-apical paraplate was not observed on any other specimen from Jameson Land.
The archaeopyle is large, The operculum is compound; it is formed by three or perhaps occasionally four or more anterior intercalary paraplates. Each opercular piece may be attached or detached from the archaeopyle margin; detached opercular pieces often occur within the cavity of the cyst.
The paracingulum may be faintly indicated by a slight depression in the cyst wall or by folding; similarly a slight depression may indicate the position of the parasulcus. Otherwise, there is no indication of furrows or of a paratabulation on the cyst surface except at the archaeopyle and rarely at the apex. None of the specimens observed possesses a kalyptra.
Emended description: Below, 1990, p. 58
Vesicle-/plate arrangement of amphiesma cop, pop, cap, 3", 3a, 6"", 7c, 6""",2"""", as, ls, rs, ps. 1" very small, no contact with PR and 2" (exsert); tegulation 4*, 3**, 4***, 7c, 4*, 4**, 3***. Growth of thecal plates ?gonyaulacoid.
Zygote cyst proximate, acavate-cornucavate, ellipsoidal and with extended, short, cone-shaped apical horn. Wall consisting of thin pedium and firm, granular- prismatic luxuria, surface evenly chagrinate or very rarely with finate, also fused granulae, which are especially coarsened at the cingular margins, the elements partially fuse distally into an incomplete, thin tegillum, that sets off partially from the basal luxuria; thecal tabulation not, partially or completely reflected, the latter in case of intraareate development of the tegillum; paratabulation scheme: NR PR/XPR/cop, pop, cap, NR"/3", 1a-arch/1a, 2a-arch/2a, 3a-arch/3a, NR""/6"", NRc/Xc/7c, NR"""/6""", NR""""/2"""", NRs/Xs/as, FM, ls, rs, ps; cop tiny, horseshoe- shaped, forming the tip of the apical protruberance and surrounded by pop; cap (V) very small; 3 apicals: very small, planate 1" (V) exsert, viii 2" (VL), x 3" (VVR); 3 anterior intercalaries: diamond-shaped 1a (LDL) and 3a (DR), fastigiate 2a (D); 6 precingulars: anteriorly bigeniculate vi-nE 1"" (VVL), anteriorly geniculate v-nE 2"" (LVL), v-nE 3"" (DL), v-nE 4"" (DDR), v-nE 5"" (RVR) and v-nE 6"" (VVR), finis 3""/4"" dorsal; cingulum laevorotatory, lightly indented, heptapartite, lati 1c-6c, fastigiate 7c; 6 postcingulars: posteriorly linear vi-nE 1""" (VVL), iv-nE 2""" (VL), iv-nE 4""" (D), iv-nE 5""" (RDR) and vi-nE 6""" (VR), posteriorly geniculate v-nE 3""" (LDL); 2 antapicals: v 1"""" towards VL, vi 2"""" antapically; sulcus partite, sulcal paraplate as, small ls and rs, large omegaform ps non-finate towards centre.
Archaeopyle: anteriorly intercalary, 1a + 2a + 3a;operculum solvate, opercular pieces secate, general opercular formula 1a-s + 2a-s + 3a-s.
Remark:
apparently, depending on the state of preservation, the tegillum may either be absent, be present as remnants on the cyst, or be entirely developed. In the latter case, the thecal tabulation is generally entirely reflected.
Affinities:
Fensome 1979, p.30-31
Pareodinia brachythelis resembles P. alaskensis Wiggins, 1975 in its possession of a coarse ornamentation, a thick cyst wall, a short apical horn and usually a type 3I archaeopyle. However, P. alaskensis is larger, more elongate and more spindle-shaped than P. brachythelis, which has an inflated, regularly rounded appearance.
P. minuta Wiggins, 1975 is of similar size to P. brachythelis and also possesses a coarse surface ornamentation and probably a three-paraplate intercalary archaeopyle. However, like P. alaskensis, P. minuta is spindle-shaped and not rounded in outline; it also differs from P. brachythelis in the morphology of its apical horn.
The ornamentation of P. verrucosa (Vozzhennikova, 1967) Wiggins, 1975, and of P. cf. P. verrucosa (herein)is distinctly coarser than that of P. brachythelis. P. verrucosa and P. kondratjevii (Vozzhennikova, 1967) Wiggins, 1975 have much longer apical horns than P. brachythelis. P. robusta Wiggins, 1975 differs from P. brachythelis in its unevenly distributed ornamentation, its elongate shape and its type 2I archaeopyle.
P. brachythelis is closely similar in shape, surface ornamentation, the nature of its archaeopyle and apical morphology to Pareodinia sp. B of Wiggins, 1975; indeed, Wiggins" specimen is probably attributable to P. brachythelis. Wiggins (1975, p.108) notes that a pre-apical series occurs at the apex of this specimen. This appears to be analogous to the pre-apical paraplate observed on the paratype of P, brachythelis.
Originally Pareodinia, subsequently (and now) Paraevansia.
Holotype: Fensome, 1979, pl.4, fig.5; text-fig.11E
Paratype: Fensome, 1979
Locus typicus: Fossilbjerget, Jameson Land, E Greenland
Stratum typicum: Bajocian-Callovian
Translation Below, 1990: LPP
Original description: Fensome 1979, p.29-30: Pareodinia brachythelis.
Diagnosis: A species of Pareodinia having a thick cyst wall densely ornamented by coarse granules or verrucae. The cyst is ovoidal with a smoothly rounded outline, and surmounted by a distinct, short mamelon-like apical horn which is often itself surmounted by a rod-like or irregularly shaped solid apicular structure; similar structures may occur elsewhere on he cyst wall, notably at the antapex. The archaeopyle is intercalary, involving the loss of three (occasionally possibly four or more) paraplates. The operculum is compound. The paracingulum is usually only weakly indicated or absent. There is no other indication of a paratabulation.
Dimensions length breadth apical horn apicular struct.
holotype 52 µm 37 µm 5 µm 2 µm
paratype 54 µm 32 µm 4 µm 2 µm
range 45(54)66 µm 31(36)42 µm 3(6)8 µm 2(3.5)5 µm
(36 spcm.)
Description:
The apical horn is of characteristic shape, with a broad base and a usually well rounded distal extremity (exclusive of any apicular structure). The horn is usually distinct from the rest of the cyst; it is variable in length but, in the type material, this does not exceed one sixth of the overall length of the cyst. Rarely the horn may be very short; indeed one specimen superficially resembles a form of Chytoeisphaeridia. The presence of a rod-like or irregularly shaped apicular structure at the distal tip of the apical horn often gives the apex a more pointed or irregular shape. Solid protruberances of irregular outline may rarely occur elsewhere on the cyst surface, especially at the antapex.
The paratype appears to possess a pre-apical paraplate on its apical horn differentiated from the rest of the cyst by a more lightly stained portion of the cyst wall; this is ornamented by a scatter of coarse, wart-like verrucae. A pre-apical paraplate was not observed on any other specimen from Jameson Land.
The archaeopyle is large, The operculum is compound; it is formed by three or perhaps occasionally four or more anterior intercalary paraplates. Each opercular piece may be attached or detached from the archaeopyle margin; detached opercular pieces often occur within the cavity of the cyst.
The paracingulum may be faintly indicated by a slight depression in the cyst wall or by folding; similarly a slight depression may indicate the position of the parasulcus. Otherwise, there is no indication of furrows or of a paratabulation on the cyst surface except at the archaeopyle and rarely at the apex. None of the specimens observed possesses a kalyptra.
Emended description: Below, 1990, p. 58
Vesicle-/plate arrangement of amphiesma cop, pop, cap, 3", 3a, 6"", 7c, 6""",2"""", as, ls, rs, ps. 1" very small, no contact with PR and 2" (exsert); tegulation 4*, 3**, 4***, 7c, 4*, 4**, 3***. Growth of thecal plates ?gonyaulacoid.
Zygote cyst proximate, acavate-cornucavate, ellipsoidal and with extended, short, cone-shaped apical horn. Wall consisting of thin pedium and firm, granular- prismatic luxuria, surface evenly chagrinate or very rarely with finate, also fused granulae, which are especially coarsened at the cingular margins, the elements partially fuse distally into an incomplete, thin tegillum, that sets off partially from the basal luxuria; thecal tabulation not, partially or completely reflected, the latter in case of intraareate development of the tegillum; paratabulation scheme: NR PR/XPR/cop, pop, cap, NR"/3", 1a-arch/1a, 2a-arch/2a, 3a-arch/3a, NR""/6"", NRc/Xc/7c, NR"""/6""", NR""""/2"""", NRs/Xs/as, FM, ls, rs, ps; cop tiny, horseshoe- shaped, forming the tip of the apical protruberance and surrounded by pop; cap (V) very small; 3 apicals: very small, planate 1" (V) exsert, viii 2" (VL), x 3" (VVR); 3 anterior intercalaries: diamond-shaped 1a (LDL) and 3a (DR), fastigiate 2a (D); 6 precingulars: anteriorly bigeniculate vi-nE 1"" (VVL), anteriorly geniculate v-nE 2"" (LVL), v-nE 3"" (DL), v-nE 4"" (DDR), v-nE 5"" (RVR) and v-nE 6"" (VVR), finis 3""/4"" dorsal; cingulum laevorotatory, lightly indented, heptapartite, lati 1c-6c, fastigiate 7c; 6 postcingulars: posteriorly linear vi-nE 1""" (VVL), iv-nE 2""" (VL), iv-nE 4""" (D), iv-nE 5""" (RDR) and vi-nE 6""" (VR), posteriorly geniculate v-nE 3""" (LDL); 2 antapicals: v 1"""" towards VL, vi 2"""" antapically; sulcus partite, sulcal paraplate as, small ls and rs, large omegaform ps non-finate towards centre.
Archaeopyle: anteriorly intercalary, 1a + 2a + 3a;operculum solvate, opercular pieces secate, general opercular formula 1a-s + 2a-s + 3a-s.
Remark:
apparently, depending on the state of preservation, the tegillum may either be absent, be present as remnants on the cyst, or be entirely developed. In the latter case, the thecal tabulation is generally entirely reflected.
Affinities:
Fensome 1979, p.30-31
Pareodinia brachythelis resembles P. alaskensis Wiggins, 1975 in its possession of a coarse ornamentation, a thick cyst wall, a short apical horn and usually a type 3I archaeopyle. However, P. alaskensis is larger, more elongate and more spindle-shaped than P. brachythelis, which has an inflated, regularly rounded appearance.
P. minuta Wiggins, 1975 is of similar size to P. brachythelis and also possesses a coarse surface ornamentation and probably a three-paraplate intercalary archaeopyle. However, like P. alaskensis, P. minuta is spindle-shaped and not rounded in outline; it also differs from P. brachythelis in the morphology of its apical horn.
The ornamentation of P. verrucosa (Vozzhennikova, 1967) Wiggins, 1975, and of P. cf. P. verrucosa (herein)is distinctly coarser than that of P. brachythelis. P. verrucosa and P. kondratjevii (Vozzhennikova, 1967) Wiggins, 1975 have much longer apical horns than P. brachythelis. P. robusta Wiggins, 1975 differs from P. brachythelis in its unevenly distributed ornamentation, its elongate shape and its type 2I archaeopyle.
P. brachythelis is closely similar in shape, surface ornamentation, the nature of its archaeopyle and apical morphology to Pareodinia sp. B of Wiggins, 1975; indeed, Wiggins" specimen is probably attributable to P. brachythelis. Wiggins (1975, p.108) notes that a pre-apical series occurs at the apex of this specimen. This appears to be analogous to the pre-apical paraplate observed on the paratype of P, brachythelis.