Back
Impletosphaeridium acropora
Impletosphaeridium acropora Warny et Wrenn, 1997
Holotype: Warny et Wrenn, 1997: Plate X, 4 and 6
Type locality: Bou Regreg S Core, Sale, Riffian Corridor, Morocco.
Stratum typicum: Messinian
Original diagnosis: Warny et Wrenn, 1997, p. 302-304
A small spheroidal acritarch carrying numerous, rigid and straight to slightly curved spines. The most distinctive feature is the sculpturing on the spines which consists of minute spinelets.
Description: Warny et Wrenn, 1997
Shape: The cyst is spherical, though usually distorted, and the abundant spines can form a mat that obscures the central body. Phragma: The cyst may be composed of two closely appressed wall layers. The central body is microgranular. Spines: The spines are rigid, may be straight or curved and taper distally. They vary in length from 3 to 9 Ám. The spines are covered with irregular, minute, distally blunt or capitate spinelets. The solid spine terminations may be acicular, but they can also appear capitate and bifurcate due to spinelets on their tip. Archeopyle: Not observed. Paratabulation: Not observed. Paracingulum: Not observed. Parasulcus: Not observed.
Dimensions: Holotype: diameter of cyst 22.0 µm; length of process 3.4 µm. Mean (x) and extreme values for n= 10 for Bou Regreg specimens: diameter of cyst 22.5-(31.9)-39.1 µm; length of process 3.4- (6.5)-8.5µm. Extreme values for n=10, for Eureka E67- 134 specimens: diameter of cyst 22-34 µm; length of process 5-7 µm.
Comparison: Although superficially similar to some copepod eggs illustrated by Van Wavering (1992), Impletosphaeridium acropora is smaller, never split open and is not dark brown in color as are many copepod eggs. I. acropora is similar to Algidasphaeridium? minutum ( Harland et al., 1980) Matsuoka and Bujak, 1988, which has a mean diameter of 35 Ám, but differs in having spines covered with spinelets. In addition, a chasmic archeopyle was not observed. I. acropora is similar to Baltisphaeridium accinctum Loeblich et Tappan (Tappan, 1980), both in shape and in bearing processes covered with spinelets. They differ in that the size of B. accinctum Loeblich et Tappan ranges from 59 to 64 Ám and the processes of this species seem to be about equal to the diameter of the central body. In contrast, the processes of I. acropora are extremely short, with an observed maximum length of 8.5 microns. In addition, it is unlikely that the specimens in the Bou Regreg sediments are reworked, because there are no other indications of reworking from a Palaeozoic source in the core. Furthermore, I. acropora also occurs in correlative Mio-Pliocene sections in the Gulf of Mexico.
Stratigraphic range: Miocene/Pliocene, entire core, samples Bl06 (182.9 m) S2 (2.99 m) (Fig. 2). This
species also occurred in the Eureka E67- 134, Desoto Canyon, Gulf of Mexico (Wrenn, unpublished data) in Miocene (Nl6/18; NNll) through Pleistocene (N22/NNl9) deposits. An acme event was noted across the Mio-Pliocene boundary (N16-18/N19-20; NN11/NN12-14).
Holotype: Warny et Wrenn, 1997: Plate X, 4 and 6
Type locality: Bou Regreg S Core, Sale, Riffian Corridor, Morocco.
Stratum typicum: Messinian
Original diagnosis: Warny et Wrenn, 1997, p. 302-304
A small spheroidal acritarch carrying numerous, rigid and straight to slightly curved spines. The most distinctive feature is the sculpturing on the spines which consists of minute spinelets.
Description: Warny et Wrenn, 1997
Shape: The cyst is spherical, though usually distorted, and the abundant spines can form a mat that obscures the central body. Phragma: The cyst may be composed of two closely appressed wall layers. The central body is microgranular. Spines: The spines are rigid, may be straight or curved and taper distally. They vary in length from 3 to 9 Ám. The spines are covered with irregular, minute, distally blunt or capitate spinelets. The solid spine terminations may be acicular, but they can also appear capitate and bifurcate due to spinelets on their tip. Archeopyle: Not observed. Paratabulation: Not observed. Paracingulum: Not observed. Parasulcus: Not observed.
Dimensions: Holotype: diameter of cyst 22.0 µm; length of process 3.4 µm. Mean (x) and extreme values for n= 10 for Bou Regreg specimens: diameter of cyst 22.5-(31.9)-39.1 µm; length of process 3.4- (6.5)-8.5µm. Extreme values for n=10, for Eureka E67- 134 specimens: diameter of cyst 22-34 µm; length of process 5-7 µm.
Comparison: Although superficially similar to some copepod eggs illustrated by Van Wavering (1992), Impletosphaeridium acropora is smaller, never split open and is not dark brown in color as are many copepod eggs. I. acropora is similar to Algidasphaeridium? minutum ( Harland et al., 1980) Matsuoka and Bujak, 1988, which has a mean diameter of 35 Ám, but differs in having spines covered with spinelets. In addition, a chasmic archeopyle was not observed. I. acropora is similar to Baltisphaeridium accinctum Loeblich et Tappan (Tappan, 1980), both in shape and in bearing processes covered with spinelets. They differ in that the size of B. accinctum Loeblich et Tappan ranges from 59 to 64 Ám and the processes of this species seem to be about equal to the diameter of the central body. In contrast, the processes of I. acropora are extremely short, with an observed maximum length of 8.5 microns. In addition, it is unlikely that the specimens in the Bou Regreg sediments are reworked, because there are no other indications of reworking from a Palaeozoic source in the core. Furthermore, I. acropora also occurs in correlative Mio-Pliocene sections in the Gulf of Mexico.
Stratigraphic range: Miocene/Pliocene, entire core, samples Bl06 (182.9 m) S2 (2.99 m) (Fig. 2). This
species also occurred in the Eureka E67- 134, Desoto Canyon, Gulf of Mexico (Wrenn, unpublished data) in Miocene (Nl6/18; NNll) through Pleistocene (N22/NNl9) deposits. An acme event was noted across the Mio-Pliocene boundary (N16-18/N19-20; NN11/NN12-14).