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Achomosphaera septata
From Williams, Lentin and Fensome 1998 - Lentin and Williams Index of Fossil Dinoflagellates:
[Achomosphaera septata, (Cookson and Eisenack, 1967b, p. 253-254, pl.42, figs.6-10; text-fig.1), Stover and Evitt, 1978, p. 139; Emendation as Spiniferites septatus: McLean, 1971, p.730.
NOW Hafniasphaera. Originally Baltisphaeridium, subsequently Spiniferites, thirdly (and now) Hafniasphaera, fourthly Achomosphaera, fifthly Rivernookia.
Holotype: Cookson and Eisenack, 1967b, pl.42, fig.6; Eisenack and Kjellström, 1975b, uppermost figure - p.984w; Fensome et al., 1996, fig.1 - p.2356.]
Locus typicus: Rivernook Member of Dilwyn Clay, Victoria, Australia
Age: Late Paleocene
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Original description as Baltisphaeridium septatum: [Cookson and Eisenack, 1967, p. 253]:
Diagnosis:
Shell spherical, thin-walled with a closely and rather coarsely apparently granular surface and a variable number of radially arranged appendages which approximate in length to the radius of the shell. A "marginal zone" often present, given the impression that the shell is thick-walled, is, in fact, due to compression.
Description:
The appendages vary in size, shape and structure. The majority narrow somewhat from a broadened base and divide distally into two or three straight or curved tapering branches with closed, pointed or minutely bifurcate tips. The larger appendages are typically hollow and septate throughout; in the finer to thread-like ones, on the contrary the degree of septation is often difficult to determine and their distal portions, at least, appear to be solid. A few of the appendages are unbranched. A pylome has been seen in a few specimens.
Dimensions:
Holotype: overall diameter c. 80 µm diameter of shell c. 57 µm, appendages 10 - 18 µm long.
Range: shell diameter c. 42 - 58 µm
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Emended description as Spiniferites septatus: [McLean, 1971, p.729-730]:
Description:
Cyst main body spherical to ovoidal with gonally and intergonally distributed processes, process position in conjunction with rarely developed, weakly defined sutural ridges indicate tabulation of 3', 0a, 6", 6c, 5?''', 1p, 1''''.
Archeopyle precingular (Type P) with simple, free operculum; corresponds to plate 3".
Cingulum reflected by processes; laevorotatory; ends displaced vertically about one cingulum width.
Hypotract ventral tabulation weakly developed, obscuring sulcal outline,
Cyst wall appears bi-layered in optical section, with compact inner layer 1.5 to 3.0 µm thick (constant for a specimen) constructed of closely appressed, bubble-like elements up to 2.5 µm in diameter.
Processes parallel sided to slightly tapering, with bluntly rounded, closed tips two to three relatively small, essential parallel sided, blunt tipped branches (that may also branch) extend from most process tips. Process bases constructed of bubble-like elements process trunks and branches hollow but compartmented by transverse septa.
Dimensions:
Observed range: main body length 43 - 49 µm, width 38 - 45 µm process length 12 - 17 µm
[Achomosphaera septata, (Cookson and Eisenack, 1967b, p. 253-254, pl.42, figs.6-10; text-fig.1), Stover and Evitt, 1978, p. 139; Emendation as Spiniferites septatus: McLean, 1971, p.730.
NOW Hafniasphaera. Originally Baltisphaeridium, subsequently Spiniferites, thirdly (and now) Hafniasphaera, fourthly Achomosphaera, fifthly Rivernookia.
Holotype: Cookson and Eisenack, 1967b, pl.42, fig.6; Eisenack and Kjellström, 1975b, uppermost figure - p.984w; Fensome et al., 1996, fig.1 - p.2356.]
Locus typicus: Rivernook Member of Dilwyn Clay, Victoria, Australia
Age: Late Paleocene
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Original description as Baltisphaeridium septatum: [Cookson and Eisenack, 1967, p. 253]:
Diagnosis:
Shell spherical, thin-walled with a closely and rather coarsely apparently granular surface and a variable number of radially arranged appendages which approximate in length to the radius of the shell. A "marginal zone" often present, given the impression that the shell is thick-walled, is, in fact, due to compression.
Description:
The appendages vary in size, shape and structure. The majority narrow somewhat from a broadened base and divide distally into two or three straight or curved tapering branches with closed, pointed or minutely bifurcate tips. The larger appendages are typically hollow and septate throughout; in the finer to thread-like ones, on the contrary the degree of septation is often difficult to determine and their distal portions, at least, appear to be solid. A few of the appendages are unbranched. A pylome has been seen in a few specimens.
Dimensions:
Holotype: overall diameter c. 80 µm diameter of shell c. 57 µm, appendages 10 - 18 µm long.
Range: shell diameter c. 42 - 58 µm
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description as Spiniferites septatus: [McLean, 1971, p.729-730]:
Description:
Cyst main body spherical to ovoidal with gonally and intergonally distributed processes, process position in conjunction with rarely developed, weakly defined sutural ridges indicate tabulation of 3', 0a, 6", 6c, 5?''', 1p, 1''''.
Archeopyle precingular (Type P) with simple, free operculum; corresponds to plate 3".
Cingulum reflected by processes; laevorotatory; ends displaced vertically about one cingulum width.
Hypotract ventral tabulation weakly developed, obscuring sulcal outline,
Cyst wall appears bi-layered in optical section, with compact inner layer 1.5 to 3.0 µm thick (constant for a specimen) constructed of closely appressed, bubble-like elements up to 2.5 µm in diameter.
Processes parallel sided to slightly tapering, with bluntly rounded, closed tips two to three relatively small, essential parallel sided, blunt tipped branches (that may also branch) extend from most process tips. Process bases constructed of bubble-like elements process trunks and branches hollow but compartmented by transverse septa.
Dimensions:
Observed range: main body length 43 - 49 µm, width 38 - 45 µm process length 12 - 17 µm