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Achomosphaera ramulifera
From Williams, Lentin and Fensome 1998 - Lentin and Williams Index of Fossil Dinoflagellates:
[Achomosphaera ramulifera, (Deflandre, 1937b, p. 74, pl.14 [al. pl.11], figs.5-6; pl.17 [al. pl.14], fig.10), Evitt, 1963, p. 163.
Originally Hystrichosphaeridium, subsequently Baltisphaeridium, thirdly (and now) Achomosphaera, fourthly Spiniferites. Lentin and Williams (1981, p.3) retained this species in Achomosphaera.
Holotype: Deflandre, 1937b, pl.14 (al. pl.11), fig.5; Fensome et al., 1991, fig.1 - p.721; fig.1 - p.725. ]
Locus typicus: Paris, France
Translation Deflandre, 1937: LPP
Age: Late Cretaceous
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Original description as Hystrichosphaeridium ramuliferum: [Deflandre 1937, p. 74-75]:
Description:
This species does not possess sutures, however at first sight resembles Hystrichosphaera ramosa. The body is ellipsoidal or more often rhomboidal, and appears to consist of one piece. There are no signs of a subdivision into plates delimited by septa.
The appendices on the body are very elegant and mostly strongly branched, and always end in three narrow horns standing normal to the axis of the process bearing them. In some specimens the narrow horns have two small terminal spinae. The largest appendices appear regularly arranged, in that they are often placed two by two at the ends of an imaginary axis through the body.
The wall, yellow or brownish yellow, is clearly less resistant than that of the other species and is often folded and crumpled.
Dimensions (approximate):
inner body 35-45 µm, with appendices: 90-100 µm.
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Description as Achomosphaera ramulifera: [Evitt 1963, p. 163]:
Diagnosis:
Test consists of a spherical to ellipsoidal central body with precingular archeopyle and furcate, spinelike processes like those in Hystrichosphaera in both structure and distribution, but without sutural ridges or septa connecting their bases as in that genus. Tips of processes not interconnected. Wall two-layered; layers typically in close contact between bases of processes.
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Supplemental descriptions:
Davey and Williams 1966, p. 49:
Description/Remarks:
Representatives of A. ramulifera occur infrequently in the Cenomanian of England and are very similar to the type material. The central body is smooth to very slightly reticulate and upon it may be traced lines marking the reflected plate boundaries. The processes are hollow, often possessing rather bulbous bases, and having usually trifurcate with bifurcating extremities. The cingular processes are commonly joined and a distinctive apical process is usually present.
The London Clay forms attributed to A. ramulifera often differ from the type material in having processes with more than three furcations, exceptionally six spines arising from one process. When six spines are present, they have apparently resulted from the elongation of the bifid tips of the three original furcations. Pastiels (1948) also recorded forms from the Ypresian of Belgium which may have more than three spines arising from a single process. The surface of the central body may be smooth or slightly granular. As with Hystrichosphaera ramosa, A. ramulifera is probably divisible into a number of varieties; one obvious variety would be those forms possessing multifurcate processes as opposed to the trifurcate processes of the type material.
Dimensions:
Cenomanian forms (4 measured): central body 40-56 µm, processes up to 36 µm.
London Clay forms (10 measured): central body 24-54 µm, processes up to 35 µm.
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Hultberg, 1985, p. 106-107:
Description:
Chorate cyst, composed of endophragm and periphragm, closely appressed between processes. The surface of both endophragm and periphragm is smooth. The shape of the cyst is subspherical to rounded rhomboidal.
The ornamentation consists of gonal and intergonal processes. The processes are triangular in cross-section. The gonal processes are trifurcate, bifid. The occasionally present intergonal processes are bifurcate, bifid. Some processes display a slightly reticulate process-tip. The processes close to the paracingulum are joined in pairs by high septa. Normally, no parasutural septa are present. However, some specimens may exhibit faint parasutural lineations.
The paratabulation, indicated by gonal processes, and sometimes, parasutural lineations, is gonyaulacacean, paratabulation formula: 3-4', 6", Xc, 5-6''', 1''''. Paraplate 1p is probably present, but is not discernible.
The archeopyle is precingular, type P, formed by the detachment of paraplate 3". Operculum free.
Paracingulum is indicated by gonal processes. Parasulcus is not indicated.
Size: 74-85 µm (diameter).
[Achomosphaera ramulifera, (Deflandre, 1937b, p. 74, pl.14 [al. pl.11], figs.5-6; pl.17 [al. pl.14], fig.10), Evitt, 1963, p. 163.
Originally Hystrichosphaeridium, subsequently Baltisphaeridium, thirdly (and now) Achomosphaera, fourthly Spiniferites. Lentin and Williams (1981, p.3) retained this species in Achomosphaera.
Holotype: Deflandre, 1937b, pl.14 (al. pl.11), fig.5; Fensome et al., 1991, fig.1 - p.721; fig.1 - p.725. ]
Locus typicus: Paris, France
Translation Deflandre, 1937: LPP
Age: Late Cretaceous
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Hystrichosphaeridium ramuliferum: [Deflandre 1937, p. 74-75]:
Description:
This species does not possess sutures, however at first sight resembles Hystrichosphaera ramosa. The body is ellipsoidal or more often rhomboidal, and appears to consist of one piece. There are no signs of a subdivision into plates delimited by septa.
The appendices on the body are very elegant and mostly strongly branched, and always end in three narrow horns standing normal to the axis of the process bearing them. In some specimens the narrow horns have two small terminal spinae. The largest appendices appear regularly arranged, in that they are often placed two by two at the ends of an imaginary axis through the body.
The wall, yellow or brownish yellow, is clearly less resistant than that of the other species and is often folded and crumpled.
Dimensions (approximate):
inner body 35-45 µm, with appendices: 90-100 µm.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Description as Achomosphaera ramulifera: [Evitt 1963, p. 163]:
Diagnosis:
Test consists of a spherical to ellipsoidal central body with precingular archeopyle and furcate, spinelike processes like those in Hystrichosphaera in both structure and distribution, but without sutural ridges or septa connecting their bases as in that genus. Tips of processes not interconnected. Wall two-layered; layers typically in close contact between bases of processes.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Supplemental descriptions:
Davey and Williams 1966, p. 49:
Description/Remarks:
Representatives of A. ramulifera occur infrequently in the Cenomanian of England and are very similar to the type material. The central body is smooth to very slightly reticulate and upon it may be traced lines marking the reflected plate boundaries. The processes are hollow, often possessing rather bulbous bases, and having usually trifurcate with bifurcating extremities. The cingular processes are commonly joined and a distinctive apical process is usually present.
The London Clay forms attributed to A. ramulifera often differ from the type material in having processes with more than three furcations, exceptionally six spines arising from one process. When six spines are present, they have apparently resulted from the elongation of the bifid tips of the three original furcations. Pastiels (1948) also recorded forms from the Ypresian of Belgium which may have more than three spines arising from a single process. The surface of the central body may be smooth or slightly granular. As with Hystrichosphaera ramosa, A. ramulifera is probably divisible into a number of varieties; one obvious variety would be those forms possessing multifurcate processes as opposed to the trifurcate processes of the type material.
Dimensions:
Cenomanian forms (4 measured): central body 40-56 µm, processes up to 36 µm.
London Clay forms (10 measured): central body 24-54 µm, processes up to 35 µm.
-----------------------------------------
Hultberg, 1985, p. 106-107:
Description:
Chorate cyst, composed of endophragm and periphragm, closely appressed between processes. The surface of both endophragm and periphragm is smooth. The shape of the cyst is subspherical to rounded rhomboidal.
The ornamentation consists of gonal and intergonal processes. The processes are triangular in cross-section. The gonal processes are trifurcate, bifid. The occasionally present intergonal processes are bifurcate, bifid. Some processes display a slightly reticulate process-tip. The processes close to the paracingulum are joined in pairs by high septa. Normally, no parasutural septa are present. However, some specimens may exhibit faint parasutural lineations.
The paratabulation, indicated by gonal processes, and sometimes, parasutural lineations, is gonyaulacacean, paratabulation formula: 3-4', 6", Xc, 5-6''', 1''''. Paraplate 1p is probably present, but is not discernible.
The archeopyle is precingular, type P, formed by the detachment of paraplate 3". Operculum free.
Paracingulum is indicated by gonal processes. Parasulcus is not indicated.
Size: 74-85 µm (diameter).