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Evansia lacryma
Evansia lacryma Mantle, 2005, p.252–254, pl.1, figs.1–9; text-figs.4A–B,5A–I.
Holotype: Mantle, 2005, pl.1, figs.1–2.
Age: Callovian–early Oxfordian.
Original description (Mantle, 2005):
Evansia? lacryma sp. nov. (Plate I, 1–9; Figs. 4A,B, 5A–I).
Holotype and type locality: Challis 11 ST1 well, sidewall core at 1552.50 m, Slide no. 2, EF T31/0. CPC no. 38822 (Plate I, 1,2).
Etymology: Latin, lacryma (tear); with reference to the cyst’s resemblance to a teardrop.
Diagnosis: Cysts proximate, cryptotabulate, acavate. Ambitus subspherical to ovoidal, surmounted by a short, rounded apical horn. Cyst wall single-layered; autophragm scabrate to densely granulate. Granules often coalesce to form fine rugulae or a microreticulum. Paracingulum weakly developed or absent. Archeopyle intercalary, type 3I, but further disintegration may occasionally involve the loss of additional intercalary and/or apical paraplates. Operculum compound.
Description: A medium-sized, proximate cyst with an ovoidal ambitus surmounted by a short apical horn and a broadly rounded antapical margin. Folding of the autophragm may produce a slight antapical bulge. The short, broad-based apical horn has a rounded distal extremity, showing no irregular thickenings or apicular structures. The cyst wall is apparently single-layered. The autophragm is scabrate to densely granulate; the granules commonly coalescing to form subdued, finely rugulate, or microreticulate sculpture. Autophragm often exhibits large lunate or undulating folds. A dark accumulation body is occasionally present towards the centre of the cyst. The cyst is essentially cryptotabulate with the paratabulation indicated only by the archeopyle margin or the paracingulum, where evident. The weakly helicoid, narrow paracingulum is faintly indicated by a slight depression in the cyst wall, by folding, or by a lack of sculpture along the paracingular sutures. The archeopyle is typically formed by the loss of the three intercalary paraplates (1a–3a), which are large and near-equant (Figs. 4 and 5). However, there is some evidence that further disintegration around the archeopyle can lead to a fourth or fifth intercalary paraplate and possibly several apical paraplates being lost. The operculum is compound and the opercular paraplates may or may not be attached to the archeopyle margin; detached opercular pieces often occur within the cyst cavity.
Dimensions (based on 30 specimens): Total length of cyst, 46 (58) 69 µm; maximum width of cyst, 34 (42) 50 µm; thickness of cyst wall, 1 (1.5) 2 µm; length of apical horn, 6 (9) 16 µm. Holotype: Total length of cyst, 60 µm; maximum width of cyst, 40 µm; thickness of cyst wall, 1.5 µm; length of apical horn, 12 µm.
Remarks: The ovoidal shape, short apical horn, and type 3I archeopyle restrict this species to assignation within the genera Evansia Pocock, 1972 emend. Below, 1990 or Paraevansia Below, 1990. Pareodinia Deflandre, 1947 emend. Gocht, 1970 has a type 2I archeopyle. The species is tentatively placed within Evansia as there is no evidence that the arrangement of the apical paraplates is of the Paragonyaulacysta type (i.e. an exert first apical paraplate) that is typical of Paraevansia (Below, 1990, pp. 72–79). However, should future SEM work demonstrate the presence of an exert first apical paraplate (1V), then the generic attribution may need to be revised.
Comparison: Evansia? lacryma sp. nov. resembles Paraevansia brachythelis (Fensome, 1979) Below 1990 in its archeopyle formation and regular rounded appearance. However, P. brachythelis has a shorter apical horn commonly surmounted by a rod-like or irregularly shaped apicular structure and possesses significantly coarser surface sculpture of grana and verrucae. The granules covering the phragma of E? lacryma are only readily discernible on well-preserved specimens, when they are occasionally observed to coalesce to form a partly rugulo-reticulate sculpture. Fensome (1979) considered Pareodinia sp. B of Wiggins (1975) to be attributable to his P. brachythelis. However, the figured specimen of P. sp. B (Wiggins, 1975, pp. 100; pl. 2) appears to be cornucavate, thus further differentiating it from E? lacryma. Paraevansia mammillata Quattrocchio and Sarjeant, 1992 is similar to E? lacryma in size, sculpture, and archeopyle morphology, but differs in having a thinner autophragm and dissimilar apical morphology (i.e., a shorter, rounder apical horn). Evansia barentsensis (Smelror, 1988) Below (1990) is differentiated by the laevigate paracingulum and the random distribution of verrucae across the rest of the phragma. The sculpture of E. wigginsii (Smelror, 1988) Below 1990 is distinctly coarser than that of E? lacryma. The type species E. granulata Pocock, 1972 is easily distinguished from E? lacryma by its dense sculpture of spinules, bacula, or clavae on the periphraghm. Evansia evittii (Pocock, 1972) Jansonius, 1986 is distinguished by its two-layered cyst wall, strongly indented archeopyle margin, and the common presence of a kalyptra or apicular structure.
Holotype: Mantle, 2005, pl.1, figs.1–2.
Age: Callovian–early Oxfordian.
Original description (Mantle, 2005):
Evansia? lacryma sp. nov. (Plate I, 1–9; Figs. 4A,B, 5A–I).
Holotype and type locality: Challis 11 ST1 well, sidewall core at 1552.50 m, Slide no. 2, EF T31/0. CPC no. 38822 (Plate I, 1,2).
Etymology: Latin, lacryma (tear); with reference to the cyst’s resemblance to a teardrop.
Diagnosis: Cysts proximate, cryptotabulate, acavate. Ambitus subspherical to ovoidal, surmounted by a short, rounded apical horn. Cyst wall single-layered; autophragm scabrate to densely granulate. Granules often coalesce to form fine rugulae or a microreticulum. Paracingulum weakly developed or absent. Archeopyle intercalary, type 3I, but further disintegration may occasionally involve the loss of additional intercalary and/or apical paraplates. Operculum compound.
Description: A medium-sized, proximate cyst with an ovoidal ambitus surmounted by a short apical horn and a broadly rounded antapical margin. Folding of the autophragm may produce a slight antapical bulge. The short, broad-based apical horn has a rounded distal extremity, showing no irregular thickenings or apicular structures. The cyst wall is apparently single-layered. The autophragm is scabrate to densely granulate; the granules commonly coalescing to form subdued, finely rugulate, or microreticulate sculpture. Autophragm often exhibits large lunate or undulating folds. A dark accumulation body is occasionally present towards the centre of the cyst. The cyst is essentially cryptotabulate with the paratabulation indicated only by the archeopyle margin or the paracingulum, where evident. The weakly helicoid, narrow paracingulum is faintly indicated by a slight depression in the cyst wall, by folding, or by a lack of sculpture along the paracingular sutures. The archeopyle is typically formed by the loss of the three intercalary paraplates (1a–3a), which are large and near-equant (Figs. 4 and 5). However, there is some evidence that further disintegration around the archeopyle can lead to a fourth or fifth intercalary paraplate and possibly several apical paraplates being lost. The operculum is compound and the opercular paraplates may or may not be attached to the archeopyle margin; detached opercular pieces often occur within the cyst cavity.
Dimensions (based on 30 specimens): Total length of cyst, 46 (58) 69 µm; maximum width of cyst, 34 (42) 50 µm; thickness of cyst wall, 1 (1.5) 2 µm; length of apical horn, 6 (9) 16 µm. Holotype: Total length of cyst, 60 µm; maximum width of cyst, 40 µm; thickness of cyst wall, 1.5 µm; length of apical horn, 12 µm.
Remarks: The ovoidal shape, short apical horn, and type 3I archeopyle restrict this species to assignation within the genera Evansia Pocock, 1972 emend. Below, 1990 or Paraevansia Below, 1990. Pareodinia Deflandre, 1947 emend. Gocht, 1970 has a type 2I archeopyle. The species is tentatively placed within Evansia as there is no evidence that the arrangement of the apical paraplates is of the Paragonyaulacysta type (i.e. an exert first apical paraplate) that is typical of Paraevansia (Below, 1990, pp. 72–79). However, should future SEM work demonstrate the presence of an exert first apical paraplate (1V), then the generic attribution may need to be revised.
Comparison: Evansia? lacryma sp. nov. resembles Paraevansia brachythelis (Fensome, 1979) Below 1990 in its archeopyle formation and regular rounded appearance. However, P. brachythelis has a shorter apical horn commonly surmounted by a rod-like or irregularly shaped apicular structure and possesses significantly coarser surface sculpture of grana and verrucae. The granules covering the phragma of E? lacryma are only readily discernible on well-preserved specimens, when they are occasionally observed to coalesce to form a partly rugulo-reticulate sculpture. Fensome (1979) considered Pareodinia sp. B of Wiggins (1975) to be attributable to his P. brachythelis. However, the figured specimen of P. sp. B (Wiggins, 1975, pp. 100; pl. 2) appears to be cornucavate, thus further differentiating it from E? lacryma. Paraevansia mammillata Quattrocchio and Sarjeant, 1992 is similar to E? lacryma in size, sculpture, and archeopyle morphology, but differs in having a thinner autophragm and dissimilar apical morphology (i.e., a shorter, rounder apical horn). Evansia barentsensis (Smelror, 1988) Below (1990) is differentiated by the laevigate paracingulum and the random distribution of verrucae across the rest of the phragma. The sculpture of E. wigginsii (Smelror, 1988) Below 1990 is distinctly coarser than that of E? lacryma. The type species E. granulata Pocock, 1972 is easily distinguished from E? lacryma by its dense sculpture of spinules, bacula, or clavae on the periphraghm. Evansia evittii (Pocock, 1972) Jansonius, 1986 is distinguished by its two-layered cyst wall, strongly indented archeopyle margin, and the common presence of a kalyptra or apicular structure.