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Cerebrocysta satchelliae
Cerebrocysta satchelliae, de Verteuil and Norris, 1996.
Holotype: Plate 14, figs. 1-4
Locus typicus: Popes Creek Section, Popes Creek, Charles County, Maryland
Stratum typicum: The lower Miocene Popes Creek Sand Member of the Calvert Formation
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Original description as Cerebrocysta satchelliae: [de Verteuil and Norris, 1996, p. 149]:
Diagnosis:
A species of Cerebrocysta in which the luxuriae consist of closely spaced pila that in places support low, irregular, solid ridges that may contain alveoles.
Archeopyle Type 2P.
Description:
Cysts intermediate sized, proximate and spherical.
The autoblast structure is uniform about the cyst and comprises homogeneous pedium ca.0.25 µm thick, and densely packed pila 1.0 to 2.5 µm high, giving the proximate luxuriae a granulate appearance in TLM (pl. 14, fig. 2). Irregularly oriented low ridges, 1.0 to 3.0 µm high (holotype 1.5 µm), occur fused with the pila and evenly distributed on the cyst surface. Ridges are variable in length from ca. 2 to 10 µm, generally 1 to 2 µm wide and may pinch and widen discontinuously along their length, giving a variable rugulate to verrucate look to the wall, even on a single cyst. Ridges are solid, or may have a central alveole, and are spaced from 1 to 4 µm apart. Ridges are non-tabular and not reticulate.
Archeopyle is Type 2P involving the second and third precingular fields in a standard gonyaulacalean precingular series; inferred 3" is weakly deltacamerate with geniculate anterior margin while inferred 2" is weakly deltaplanate with rectilinear anterior margin (pl. 13, fig. 13). The operculum is compound and free.
Dimensions:
Maximum cyst diameter, excluding ridges, 47(60)76 µm, holotype 58 µm. Twenty-five specimens measured.
Discussion:
The archeopyle in Cerebrocysta satchelliae is inferred to comprise the second and third precingular fields in a standard gonyaulacalean precingular series with mid-dorsal deltacamerate 3". This condition was true for all specimens in which the archeopyle could be clearly discerned. The contrasting situation occurs in the biplacoid precingular archeopyle of Bitectatodinium tepikiense, in which, using the same criteria, it is 3" and 4" that are involved in archeopyle formation. In Cerebrocysta bartonensis, the type species, the precingular archeopyle can include either 2", 4" or both (Bujak 1980). Cerebrocysta namocensis has a Type 2P archeopyle involving fields 3" and 4". It is significant that the taxon (?)Bitectatodinium sp. Biffi and Manum 1988, herein provisionally synonymized with Cerebrocysta satchelliae, is described as having a Type 2P archeopyle involving 3" and 4". Both of the illustrated specimens (Biffi and Manum 1988, pl. 10, figs. 8,12) are equivocal in this respect. However, the specimen illustrated in low focus by Manum et al. (1989, pl. 4, fig. 11) as Bitectatodinium? sp. I and also provisionally synonymized with the new species, does appear to have a 2P archeopyle involving 3" and 4". Cerebrocysta mediterranea, which has a psilate limbus surrounding the archeopyle suture, is also described as having the archeopyle formed by loss of the third and fourth precingular fields. The illustration of the holotype of Cerebrocysta mediterranea (Biffi and Manum 1988, pl. 11, fig. 11), however, and that of a paratype (pl. 11, fig. 12), suggest to us that at least in these two cases the archeopyle was formed by loss of rectilinear 2" and geniculate 3". It may be possible, therefore, that the biplacoid precingular archeopyle in Cerebrocysta satchelliae may involve either 2" or 4" in conjunction with 3".
Affinities/Comparison:
The new species is significantly larger than Cerebrocysta bartonensis, which has a maximum diameter <30 µm. The detailed structure of the proximate luxuriae in Cerebrocysta bartonensis is not known. Cerebrocysta mediterranea is comparable in size, although slightly larger than Cerebrocysta satchelliae, but is characterized by a well defined reticulum formed by the ridges of the proximate luxuriae. The taxa described by Biffi and Manum (1988) as Cerebrocysta (?) sp. A and sp. B are both broadly similar to Cerebrocysta satchelliae in the variability of height, length and distribution style of the proximate ridges. These two taxa are smaller than the new species, ovoidal to subspherical rather than spherical in shape, and have a simple Type P precingular archeopyle. Cerebrocysta namocensis, Bitectatodinium tepikiense and Pyxidinopsis challengerensis all lack the pila that characterize the prismatic luxuriae of Cerebrocysta satchelliae.
Holotype: Plate 14, figs. 1-4
Locus typicus: Popes Creek Section, Popes Creek, Charles County, Maryland
Stratum typicum: The lower Miocene Popes Creek Sand Member of the Calvert Formation
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Cerebrocysta satchelliae: [de Verteuil and Norris, 1996, p. 149]:
Diagnosis:
A species of Cerebrocysta in which the luxuriae consist of closely spaced pila that in places support low, irregular, solid ridges that may contain alveoles.
Archeopyle Type 2P.
Description:
Cysts intermediate sized, proximate and spherical.
The autoblast structure is uniform about the cyst and comprises homogeneous pedium ca.0.25 µm thick, and densely packed pila 1.0 to 2.5 µm high, giving the proximate luxuriae a granulate appearance in TLM (pl. 14, fig. 2). Irregularly oriented low ridges, 1.0 to 3.0 µm high (holotype 1.5 µm), occur fused with the pila and evenly distributed on the cyst surface. Ridges are variable in length from ca. 2 to 10 µm, generally 1 to 2 µm wide and may pinch and widen discontinuously along their length, giving a variable rugulate to verrucate look to the wall, even on a single cyst. Ridges are solid, or may have a central alveole, and are spaced from 1 to 4 µm apart. Ridges are non-tabular and not reticulate.
Archeopyle is Type 2P involving the second and third precingular fields in a standard gonyaulacalean precingular series; inferred 3" is weakly deltacamerate with geniculate anterior margin while inferred 2" is weakly deltaplanate with rectilinear anterior margin (pl. 13, fig. 13). The operculum is compound and free.
Dimensions:
Maximum cyst diameter, excluding ridges, 47(60)76 µm, holotype 58 µm. Twenty-five specimens measured.
Discussion:
The archeopyle in Cerebrocysta satchelliae is inferred to comprise the second and third precingular fields in a standard gonyaulacalean precingular series with mid-dorsal deltacamerate 3". This condition was true for all specimens in which the archeopyle could be clearly discerned. The contrasting situation occurs in the biplacoid precingular archeopyle of Bitectatodinium tepikiense, in which, using the same criteria, it is 3" and 4" that are involved in archeopyle formation. In Cerebrocysta bartonensis, the type species, the precingular archeopyle can include either 2", 4" or both (Bujak 1980). Cerebrocysta namocensis has a Type 2P archeopyle involving fields 3" and 4". It is significant that the taxon (?)Bitectatodinium sp. Biffi and Manum 1988, herein provisionally synonymized with Cerebrocysta satchelliae, is described as having a Type 2P archeopyle involving 3" and 4". Both of the illustrated specimens (Biffi and Manum 1988, pl. 10, figs. 8,12) are equivocal in this respect. However, the specimen illustrated in low focus by Manum et al. (1989, pl. 4, fig. 11) as Bitectatodinium? sp. I and also provisionally synonymized with the new species, does appear to have a 2P archeopyle involving 3" and 4". Cerebrocysta mediterranea, which has a psilate limbus surrounding the archeopyle suture, is also described as having the archeopyle formed by loss of the third and fourth precingular fields. The illustration of the holotype of Cerebrocysta mediterranea (Biffi and Manum 1988, pl. 11, fig. 11), however, and that of a paratype (pl. 11, fig. 12), suggest to us that at least in these two cases the archeopyle was formed by loss of rectilinear 2" and geniculate 3". It may be possible, therefore, that the biplacoid precingular archeopyle in Cerebrocysta satchelliae may involve either 2" or 4" in conjunction with 3".
Affinities/Comparison:
The new species is significantly larger than Cerebrocysta bartonensis, which has a maximum diameter <30 µm. The detailed structure of the proximate luxuriae in Cerebrocysta bartonensis is not known. Cerebrocysta mediterranea is comparable in size, although slightly larger than Cerebrocysta satchelliae, but is characterized by a well defined reticulum formed by the ridges of the proximate luxuriae. The taxa described by Biffi and Manum (1988) as Cerebrocysta (?) sp. A and sp. B are both broadly similar to Cerebrocysta satchelliae in the variability of height, length and distribution style of the proximate ridges. These two taxa are smaller than the new species, ovoidal to subspherical rather than spherical in shape, and have a simple Type P precingular archeopyle. Cerebrocysta namocensis, Bitectatodinium tepikiense and Pyxidinopsis challengerensis all lack the pila that characterize the prismatic luxuriae of Cerebrocysta satchelliae.