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Ampulladinium minutispinosum
Ampulladinium minutispinosum, Parker in Riding and Helby, 2001g, p. 183.
Holotype: Riding and Helby, 2001g, figs.2I-L.
Stratigraphical distribution: Ampulladinium variabile ranges from the Tithonian upper Dinogodinium jurasscum Zone (5aii) to the lower Pseudoceratium iehiense Zone (4ciia) (Foster, this volume; Helby & Partridge, in prep.)
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Original description: [Riding & Helby, 2001g]:
Description:
A holocavate species of Ampulladinium which is slightly dorsoventrally compressed. It is trilobite and subtriangular in outline; a slight antapical concavity may be resent between the hypocystal lobes.
The Autophragm as about 1 to 1.5 µm thick and overlain by a thin (<0.5 µm), finely but irregularly reticulate ectophragm. Short (1-5 µm), solid, slender processes support the outer layer of the ectophragm. Where this outer layer is missing, the processes may be thorn-shaped and appear to taper to sharp points distally. The density of these elements varies from relatively sparse to extremely dense, although they have not been observed on the parasulcus. The density of the processes tends to be greatest in the peripheral areas of the cyst, especially on the antapical lateral lobes. The ectophragm may be absent in poorly-preserved material, suggesting that it may be susceptible to physio-chemical degradation. In extreme cases, the processes may also be degraded. The operculum is small, flattened and short accessory archeopyle sutures are normally developed.
Dimensions (µm, n=25): Min.(Mean)Max.
Length of the entire cyst: 37(43)52
Length of the loisthocyst: 32(39)50
Width of epicyst incl. ornament*: 14(21)31
Width of hypocyst incl. ornament**: 34(44)59
Length of processes/height of ectocoel: 1(2)5
* - measured at the principle archeopyle suture
* - measured at the antapex
The measure specimens are from conventional core samples in Lorikeet-1 well at 1759.10m and 1756.70m and Mutineer-1B well at 3132.25m, sidewall core samples +from jurabi-1 well at 1140.00m and Scafell-1 well at 1418.00m and ditch cuttings from avocet-1A well between 1775.00m and 1780.00m, Broome-1 Bore at 297.79m and Peak-1 well between 1493.54m and 1496.59m.
Comments:
This species is highly variable in morphology due to apparent susceptibility of the ectophragm to physio-chemical degradation. In well-preserved material, a continuous ectophragm is supported by numerous processes. However, the ectophragm is frequently incomplete. In poorly-preserved material, both the processes/spines and ectophragm are missing. Most specimens of A. variabile are small and the majority loisthocysts. The ectophragm is normally narrow; from 1-5µm across. In some specimens the processes are longest at the antapical-lateral lobs, broadening the ectocoel in those areas.
Affinities/Comparison:
Ampulladinium variabile closely resembles Woodinia bensonii Riding & Helby (this volume) in morphology. However, the latter is significantly smaller, frequently more elongate and antapically concave. Furthermore, W. bensonii is not holocavate and is characterized by intratabular areas of ornamentation styles or differentiated Autophragm on the major paraplate series.
Holotype: Riding and Helby, 2001g, figs.2I-L.
Stratigraphical distribution: Ampulladinium variabile ranges from the Tithonian upper Dinogodinium jurasscum Zone (5aii) to the lower Pseudoceratium iehiense Zone (4ciia) (Foster, this volume; Helby & Partridge, in prep.)
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Riding & Helby, 2001g]:
Description:
A holocavate species of Ampulladinium which is slightly dorsoventrally compressed. It is trilobite and subtriangular in outline; a slight antapical concavity may be resent between the hypocystal lobes.
The Autophragm as about 1 to 1.5 µm thick and overlain by a thin (<0.5 µm), finely but irregularly reticulate ectophragm. Short (1-5 µm), solid, slender processes support the outer layer of the ectophragm. Where this outer layer is missing, the processes may be thorn-shaped and appear to taper to sharp points distally. The density of these elements varies from relatively sparse to extremely dense, although they have not been observed on the parasulcus. The density of the processes tends to be greatest in the peripheral areas of the cyst, especially on the antapical lateral lobes. The ectophragm may be absent in poorly-preserved material, suggesting that it may be susceptible to physio-chemical degradation. In extreme cases, the processes may also be degraded. The operculum is small, flattened and short accessory archeopyle sutures are normally developed.
Dimensions (µm, n=25): Min.(Mean)Max.
Length of the entire cyst: 37(43)52
Length of the loisthocyst: 32(39)50
Width of epicyst incl. ornament*: 14(21)31
Width of hypocyst incl. ornament**: 34(44)59
Length of processes/height of ectocoel: 1(2)5
* - measured at the principle archeopyle suture
* - measured at the antapex
The measure specimens are from conventional core samples in Lorikeet-1 well at 1759.10m and 1756.70m and Mutineer-1B well at 3132.25m, sidewall core samples +from jurabi-1 well at 1140.00m and Scafell-1 well at 1418.00m and ditch cuttings from avocet-1A well between 1775.00m and 1780.00m, Broome-1 Bore at 297.79m and Peak-1 well between 1493.54m and 1496.59m.
Comments:
This species is highly variable in morphology due to apparent susceptibility of the ectophragm to physio-chemical degradation. In well-preserved material, a continuous ectophragm is supported by numerous processes. However, the ectophragm is frequently incomplete. In poorly-preserved material, both the processes/spines and ectophragm are missing. Most specimens of A. variabile are small and the majority loisthocysts. The ectophragm is normally narrow; from 1-5µm across. In some specimens the processes are longest at the antapical-lateral lobs, broadening the ectocoel in those areas.
Affinities/Comparison:
Ampulladinium variabile closely resembles Woodinia bensonii Riding & Helby (this volume) in morphology. However, the latter is significantly smaller, frequently more elongate and antapically concave. Furthermore, W. bensonii is not holocavate and is characterized by intratabular areas of ornamentation styles or differentiated Autophragm on the major paraplate series.