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Achomosphaera spongiosa
From Williams, Lentin and Fensome 1998 - Lentin and Williams Index of Fossil Dinoflagellates:
[Achomosphaera spongiosa, Matsuoka and Bujak, 1988, p. 37-38, pl.1, figs.5-7; pl.2, figs.1-3.
Holotype: Matsuoka and Bujak, 1988, pl.2, fig.2]
Paratypes: Matsuoka and Bujak, 1988
Locus typicus: Navarin Basin COST No. 1 well, Navarin Basin, Bering Sea
Stratum typicum: H. campanula Zone; Late Oligocene to Early Miocene
Age: Late Oligocene-Early Miocene
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Original description: [Matsuoka and Bujak, 1988, p. 37-38]:
Diagnosis:
Ellipsoidal to ovoidal proximochorate cyst comprising two layers which are mostly in contact; periphragm thick, spongy and granular: endophragm relatively thin and smooth. Apical and antapical horns absent. Parasutures occasionally visible.
Gonal processes with bi- or trifurcate distal extremities. Sutural processes absent.
Archeopyle precingular, formed by the loss of plate 3".
Description:
The cyst is intermediate to small in size, mostly ovoidal to ellipsoidal but rarely subspherical, without apical or antapical horns. The periphragm is spongy, but corroded specimens have a coarsely reticulate appearance.
The processes are gonal and solid with trifurcate and rarely bifurcate endings. Stalks of processes are sometimes ornamented with grana and in poorly preserved specimens are perforated due to corrosion.
The parasutures are strongly reduced and occasionally faintly visible.
The paratabulation is 4', ?a, 6", 6c, 6''', 1p, 1'''', xs.
The archeopyle is precingular, formed by loss of the 3" paraplate. The operculum is free.
Thecal affinity: Probably Gonyaulacaceae based on its paratabulation.
Dimensions:
Holotype; length of cyst 52 µm, width 45 µm, length of processes up to 12 µm.
Range; length of cyst 41-58 µm, width of cyst 33-48 µm, length of processes 8-13 µm. Number of specimens measured 10.
Affinities:
The species described as Achomosphaera sp. A by Matsuoka is identical with Achomosphaera spongiosa. Many of Matsuoka' s specimens are corroded and their periphragm appeared to be reticulate, but relatively well-preserved specimens show the spongy wall structure and absence of reticulation.
Wiggins (1986) recorded the presence of forms intermediate between Spiniferites sp. (Wiggins, 1986, pl, 1, figs. 1,2) and Achomosphaera sp. (Wiggins, 1986, pl. 1, fig. 4) in the upper Miocene of the Bering Sea which are considered to be synonymous with A. spongiosa.
Achomosphaera spongiosa resembles A. sagena Davey and Williams, A. callosa Matsuoka, and A. crassipellis (Deflandre and Cookson) in possessing a relatively thick wall and occasionally faint parasutures. It differs from A. sagena in having a thinner endophragm and relatively elongate cyst body, and from A. callosa and A. crassipellis in having a spongy and thinner periphragm.
[Achomosphaera spongiosa, Matsuoka and Bujak, 1988, p. 37-38, pl.1, figs.5-7; pl.2, figs.1-3.
Holotype: Matsuoka and Bujak, 1988, pl.2, fig.2]
Paratypes: Matsuoka and Bujak, 1988
Locus typicus: Navarin Basin COST No. 1 well, Navarin Basin, Bering Sea
Stratum typicum: H. campanula Zone; Late Oligocene to Early Miocene
Age: Late Oligocene-Early Miocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Matsuoka and Bujak, 1988, p. 37-38]:
Diagnosis:
Ellipsoidal to ovoidal proximochorate cyst comprising two layers which are mostly in contact; periphragm thick, spongy and granular: endophragm relatively thin and smooth. Apical and antapical horns absent. Parasutures occasionally visible.
Gonal processes with bi- or trifurcate distal extremities. Sutural processes absent.
Archeopyle precingular, formed by the loss of plate 3".
Description:
The cyst is intermediate to small in size, mostly ovoidal to ellipsoidal but rarely subspherical, without apical or antapical horns. The periphragm is spongy, but corroded specimens have a coarsely reticulate appearance.
The processes are gonal and solid with trifurcate and rarely bifurcate endings. Stalks of processes are sometimes ornamented with grana and in poorly preserved specimens are perforated due to corrosion.
The parasutures are strongly reduced and occasionally faintly visible.
The paratabulation is 4', ?a, 6", 6c, 6''', 1p, 1'''', xs.
The archeopyle is precingular, formed by loss of the 3" paraplate. The operculum is free.
Thecal affinity: Probably Gonyaulacaceae based on its paratabulation.
Dimensions:
Holotype; length of cyst 52 µm, width 45 µm, length of processes up to 12 µm.
Range; length of cyst 41-58 µm, width of cyst 33-48 µm, length of processes 8-13 µm. Number of specimens measured 10.
Affinities:
The species described as Achomosphaera sp. A by Matsuoka is identical with Achomosphaera spongiosa. Many of Matsuoka' s specimens are corroded and their periphragm appeared to be reticulate, but relatively well-preserved specimens show the spongy wall structure and absence of reticulation.
Wiggins (1986) recorded the presence of forms intermediate between Spiniferites sp. (Wiggins, 1986, pl, 1, figs. 1,2) and Achomosphaera sp. (Wiggins, 1986, pl. 1, fig. 4) in the upper Miocene of the Bering Sea which are considered to be synonymous with A. spongiosa.
Achomosphaera spongiosa resembles A. sagena Davey and Williams, A. callosa Matsuoka, and A. crassipellis (Deflandre and Cookson) in possessing a relatively thick wall and occasionally faint parasutures. It differs from A. sagena in having a thinner endophragm and relatively elongate cyst body, and from A. callosa and A. crassipellis in having a spongy and thinner periphragm.