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Achomosphaera progranulata
Achomosphaera progranulata, Vieira, M. et al., 2018, p. 183, 185
Holotype: Vieira, M. et al., 2018, Plate 1, figures 7–9
Type locality: southern part of the Ormen Lange field (Norway) over the Danian-aged reservoir
Local stratigraphical range: Danian (Early Paleocene)
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Original description: [Vieira, M. et al., 2018]:
Diagnosis:
Chorate to proximochorate cysts, spherical to subspherical in shape, with precingular archaeopyle.
Cyst composed of two layers, periphragm and endophragm adpressed between processes; the surface of the periphragm is very thin and psilate. The endophragm is thick and fibrous up to 5.5 µm, with numerous evenly distributed grana.
Processes are 14–26 µm in length and 3.5–5.5 µm in width. The processes exhibit a gonal position, hollow to occasionally solid, and often possessing bulbous bases; tips of the processes are not connected and usually trifurcate with bifurcation and open distally.
Dimensions:
Holotype: cyst diameter 79 µm, width 74 µm (without processes); length 120 µm, width 115 µm (with processes), length of processes 25 µm, width of processes 4.5 µm
20 specimens measured: Diameter of cyst body 72 (82) 96 µm, cyst diameter with processes 85 (108) 129 µm, length of processes 14 (20)
26 µm, width 3.5 (4.5) 5.5 µm.
Affinities/Comparison:
Fensome & Williams (2004) stated that Achomosphaera Evitt (1963) has a gonal and sometimes a parasutural archeopyle with hollow or generally solid processes. They also stated that Achomosphaera differs from Spiniferites (Mantell 1850) Sarjeant 1970 in lacking parasutures.
Quatrocchio & Sarjeant (2003) proposed to relegate Hafniasphaera Hansen (1977), to a subspecies of Spiniferites. However, Fensome et al. (2009) reinstated Hafniasphaera as a separate genus similar to Spiniferites but with vesiculate processes. Fensome et al. (2009) stated that Hafniasphaera is separated from Spiniferites as a group of forms that have a range mainly within the latest Cretaceous to earliest Paleogene. Schiøler (2005) transferred Pseudospiniferites manumii Lund (2002) to Spiniferites as a species of that genus which is characterised by its conspicuous closely spaced vermiculate ornament. This taxon is well known from sections of Early Oligocene age in north-west
Europe. The granulation and the thickness of the central body with the nature of the processes (shorter and thinner) are characteristics of this type and distinguish it from other species in the genus, and in particular Achomosphaera eggadania sp. nov. This species is similar to Hafniasphaera cryptovesiculata Hansen (1977); however, it differs in the absence of vesiculation on the processes. It also differs from Hafniasphaera graciosa Hansen (1977) by its thicker wall and more robust, rather than hollow, processes.
Holotype: Vieira, M. et al., 2018, Plate 1, figures 7–9
Type locality: southern part of the Ormen Lange field (Norway) over the Danian-aged reservoir
Local stratigraphical range: Danian (Early Paleocene)
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Vieira, M. et al., 2018]:
Diagnosis:
Chorate to proximochorate cysts, spherical to subspherical in shape, with precingular archaeopyle.
Cyst composed of two layers, periphragm and endophragm adpressed between processes; the surface of the periphragm is very thin and psilate. The endophragm is thick and fibrous up to 5.5 µm, with numerous evenly distributed grana.
Processes are 14–26 µm in length and 3.5–5.5 µm in width. The processes exhibit a gonal position, hollow to occasionally solid, and often possessing bulbous bases; tips of the processes are not connected and usually trifurcate with bifurcation and open distally.
Dimensions:
Holotype: cyst diameter 79 µm, width 74 µm (without processes); length 120 µm, width 115 µm (with processes), length of processes 25 µm, width of processes 4.5 µm
20 specimens measured: Diameter of cyst body 72 (82) 96 µm, cyst diameter with processes 85 (108) 129 µm, length of processes 14 (20)
26 µm, width 3.5 (4.5) 5.5 µm.
Affinities/Comparison:
Fensome & Williams (2004) stated that Achomosphaera Evitt (1963) has a gonal and sometimes a parasutural archeopyle with hollow or generally solid processes. They also stated that Achomosphaera differs from Spiniferites (Mantell 1850) Sarjeant 1970 in lacking parasutures.
Quatrocchio & Sarjeant (2003) proposed to relegate Hafniasphaera Hansen (1977), to a subspecies of Spiniferites. However, Fensome et al. (2009) reinstated Hafniasphaera as a separate genus similar to Spiniferites but with vesiculate processes. Fensome et al. (2009) stated that Hafniasphaera is separated from Spiniferites as a group of forms that have a range mainly within the latest Cretaceous to earliest Paleogene. Schiøler (2005) transferred Pseudospiniferites manumii Lund (2002) to Spiniferites as a species of that genus which is characterised by its conspicuous closely spaced vermiculate ornament. This taxon is well known from sections of Early Oligocene age in north-west
Europe. The granulation and the thickness of the central body with the nature of the processes (shorter and thinner) are characteristics of this type and distinguish it from other species in the genus, and in particular Achomosphaera eggadania sp. nov. This species is similar to Hafniasphaera cryptovesiculata Hansen (1977); however, it differs in the absence of vesiculation on the processes. It also differs from Hafniasphaera graciosa Hansen (1977) by its thicker wall and more robust, rather than hollow, processes.