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Bitectatodinium arborichiarum
Bitectatodinium? arborichiarum, Louwye, 1999, p.112,115, pl.1, figs.1–8.
Questionable assignment by Louwye, 1999, p.112.
Holotype: Louwye, 1999, pl.1, figs.1–3.
Type stratum: Diest Formation, Upper Miocene.
Occurrence: Upper Miocene (Diest Formation) of northern Belgium (this study); Middle Miocene of the Netherlands as cf. Habibacysta sp. in Head (1994a).
Age: late Miocene.
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Original description: [Louwye, 1999, p.112,115]:
Diagnosis:
Spherical, holocavate cyst with a solid endophragm densely covered with short, solid rods which form a periphragm. The rods support a thin, hyaline and continuous ectophragm. A small apical protuberance formed by the endophragm is mostly present.
Archeopyle type 2P, probably plates 200 and 300. The operculum is mostly free, occasionally adherent, with separated opercular plates.
Description:
The endophragm has a thickness of less than 0.4 µm. The length of the rods is uniform on an individual and the distribution is nontabular. The average distance between adjacent rods varies from ca. 0.5 to 1.5 µm. The rods are mostly simple, but proximal or distal bifurcation occurs occasionally. The thickness of the simple rods is ca. 0.25 µm and even over the greater part of the length. The rods are proximally and distally slightly expanded.
The smooth ectophragm is very thin and in transmitted light best visible at the margins of the cyst.
The archeopyle has well defined angles and is the only expression of tabulation. Accessory archeopyle sutures were observed on a few specimens.
Dimensions:
Holotype: diameter cyst body, 40 µm; length of rods, 2 µm; height of apical boss, 1– 1.5 µm.
Range: diameter cyst body, 33(39)49 µm; length of rods, 2(2.5)3 µm. Number of specimens measured: 16.
Affinities/Comparison:
Habibacysta tectata Head et al., 1989b is most similar but differs by the distinctive precingular archeopyle formed by the loss of only plate 300, the discontinuous ectophragm and the smaller wall thickness. ‘Headinium miocenicum’ Zevenboom and Santarelli (ms name) in Zevenboom, 1995 (Middle to Upper Miocene, The Netherlands) appears to differ by the 3P archeopyle, the larger size [39 (54) 60 µm] and hollow, higher [5 (6) 7 µm] rods. Bitectatodinium raedwaldii Head, 1997 is characterised by an ornamentation of distally fused pili with variable length. At a first glance, Filisphaera filifera auct. non Bujak, 1984 in Rusbu¨lt and Strauss (1992) (Middle Miocene, Mecklenburg, Germany) resembles B.? arborichiarum and may be conspecific.
Remarks:
The new species possesses characteristics of the genus Bitectatodinium Wilson, 1973 but differs in its wall structure, hence the questioned assignment to this genus. The wall of Bitectatodinium is characterised by a dense inner layer and a tectate spongy outer layer, according to Wilson, 1973. Head (1994b) describes the wall structure of this genus as having a luxuria comprising lamellar elements arising from raised bases and subcircular in plan view.
Questionable assignment by Louwye, 1999, p.112.
Holotype: Louwye, 1999, pl.1, figs.1–3.
Type stratum: Diest Formation, Upper Miocene.
Occurrence: Upper Miocene (Diest Formation) of northern Belgium (this study); Middle Miocene of the Netherlands as cf. Habibacysta sp. in Head (1994a).
Age: late Miocene.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Louwye, 1999, p.112,115]:
Diagnosis:
Spherical, holocavate cyst with a solid endophragm densely covered with short, solid rods which form a periphragm. The rods support a thin, hyaline and continuous ectophragm. A small apical protuberance formed by the endophragm is mostly present.
Archeopyle type 2P, probably plates 200 and 300. The operculum is mostly free, occasionally adherent, with separated opercular plates.
Description:
The endophragm has a thickness of less than 0.4 µm. The length of the rods is uniform on an individual and the distribution is nontabular. The average distance between adjacent rods varies from ca. 0.5 to 1.5 µm. The rods are mostly simple, but proximal or distal bifurcation occurs occasionally. The thickness of the simple rods is ca. 0.25 µm and even over the greater part of the length. The rods are proximally and distally slightly expanded.
The smooth ectophragm is very thin and in transmitted light best visible at the margins of the cyst.
The archeopyle has well defined angles and is the only expression of tabulation. Accessory archeopyle sutures were observed on a few specimens.
Dimensions:
Holotype: diameter cyst body, 40 µm; length of rods, 2 µm; height of apical boss, 1– 1.5 µm.
Range: diameter cyst body, 33(39)49 µm; length of rods, 2(2.5)3 µm. Number of specimens measured: 16.
Affinities/Comparison:
Habibacysta tectata Head et al., 1989b is most similar but differs by the distinctive precingular archeopyle formed by the loss of only plate 300, the discontinuous ectophragm and the smaller wall thickness. ‘Headinium miocenicum’ Zevenboom and Santarelli (ms name) in Zevenboom, 1995 (Middle to Upper Miocene, The Netherlands) appears to differ by the 3P archeopyle, the larger size [39 (54) 60 µm] and hollow, higher [5 (6) 7 µm] rods. Bitectatodinium raedwaldii Head, 1997 is characterised by an ornamentation of distally fused pili with variable length. At a first glance, Filisphaera filifera auct. non Bujak, 1984 in Rusbu¨lt and Strauss (1992) (Middle Miocene, Mecklenburg, Germany) resembles B.? arborichiarum and may be conspecific.
Remarks:
The new species possesses characteristics of the genus Bitectatodinium Wilson, 1973 but differs in its wall structure, hence the questioned assignment to this genus. The wall of Bitectatodinium is characterised by a dense inner layer and a tectate spongy outer layer, according to Wilson, 1973. Head (1994b) describes the wall structure of this genus as having a luxuria comprising lamellar elements arising from raised bases and subcircular in plan view.