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Reticulatosphaera valdereticulata
Reticulatosphaera valdereticulata, Casas-Gallego, M. et al., 2021, p. 341-342
Holotype: Casas-Gallego, M. et al., 2021, Plate 3, figure 3
Type locality: Gannet Field (UK North Sea)
Local stratigraphical range: Lower Oligocene (Rupelian)
Original description: Casas-Gallego, M. et al., 2021:
Diagnosis:
A species of Reticulatosphaera with the distal part of the processes branching into 3–5 thinner branches which meet with those derived from adjacent processes to form an extremely dense net-like structure of trabeculae. Occasionally, trabeculae are slightly membranous.
Dimensions:
Holotype: Cyst length 63–70 µm
15 specimens measured: Diameter range, including processes: 55–90 µm
Affinities/Comparison:
Reticulatosphaera valdereticulata differs from the only other species within the genus, Reticulatosphaera actinocoronata, in possessing a distinctive dense network of trabeculae. Bujak and Matsuoka (1986) transferred the species Cleistosphaeridium actinocoronatum Benedek 1972 to the genus Reticulatosphaera and emended its diagnosis, making reference to ‘an irregular network formed by distal trabeculae connecting adjacent processes’. While this is true in some specimens of Reticulatosphaera actinocoronata (see Plate 3, figure 11), the processes do not meet distally in a significant proportion of specimens (see Plate 3, figures 10 and 12). Furthermore, the distal parts of processes in Reticulatosphaera actinocoronata branch into thinner, primary ramifications which further branch into secondary, and even tertiary, progressively thinner ramifications (see Plate 3, figure 10). By contrast, in Reticulatosphaera valdereticulata, branching that gives rise to process-supported trabeculae maintains the same thickness throughout the cyst. Reticulatosphaera valdereticulata exhibits a much denser
net-like arrangement of processes and is comparable to some specimens attributed to Reticulatosphaera actinocoronata by Brinkhuis and Biffi (1993) from the Rupelian of Italy. We consider that the difference between such specimens and typical Reticulatosphaera actinocoronata represents a qualitative step forward in a morphological transition which, together with its biostratigraphical applicability, argues for the erection of a new species. An additional, potentially diagnostic feature of Reticulatosphera valdereticulata is its smaller average central
body size compared to that of Reticulatosphaera actinocoronata, which occasionally results in specimens with processes emerging extremely close to each other (Plate 3, figures 4 and 9).
Reticulatosphaera valdereticulata is also somewhat similar to species of Nematosphaeropsis. However, the trabecular network of the latter consists of pairs of trabeculae running parallel to parasutural features, giving rise to a systematically organised network (Wrenn 1988). Moreover, Nematosphaeropsis possesses gonal (and sometimes also intergonal) processes. By contrast, the trabecular network of Reticulatosphaera valdereticulata is made up of more randomly organised single trabeculae, and supporting processes are intratabular.
Eatonicysta ursulae also possesses solid processes that support a dense reticulum (Stover and Evitt 1978). However, the archaeopyle in Eatonicysta ursulae is apical and the processes are flexible, which often results in specimens with preserved flexed processes. Processes in Reticulatosphaera valdereticulata are typically rigid, barely ever observed flexed.
Holotype: Casas-Gallego, M. et al., 2021, Plate 3, figure 3
Type locality: Gannet Field (UK North Sea)
Local stratigraphical range: Lower Oligocene (Rupelian)
Original description: Casas-Gallego, M. et al., 2021:
Diagnosis:
A species of Reticulatosphaera with the distal part of the processes branching into 3–5 thinner branches which meet with those derived from adjacent processes to form an extremely dense net-like structure of trabeculae. Occasionally, trabeculae are slightly membranous.
Dimensions:
Holotype: Cyst length 63–70 µm
15 specimens measured: Diameter range, including processes: 55–90 µm
Affinities/Comparison:
Reticulatosphaera valdereticulata differs from the only other species within the genus, Reticulatosphaera actinocoronata, in possessing a distinctive dense network of trabeculae. Bujak and Matsuoka (1986) transferred the species Cleistosphaeridium actinocoronatum Benedek 1972 to the genus Reticulatosphaera and emended its diagnosis, making reference to ‘an irregular network formed by distal trabeculae connecting adjacent processes’. While this is true in some specimens of Reticulatosphaera actinocoronata (see Plate 3, figure 11), the processes do not meet distally in a significant proportion of specimens (see Plate 3, figures 10 and 12). Furthermore, the distal parts of processes in Reticulatosphaera actinocoronata branch into thinner, primary ramifications which further branch into secondary, and even tertiary, progressively thinner ramifications (see Plate 3, figure 10). By contrast, in Reticulatosphaera valdereticulata, branching that gives rise to process-supported trabeculae maintains the same thickness throughout the cyst. Reticulatosphaera valdereticulata exhibits a much denser
net-like arrangement of processes and is comparable to some specimens attributed to Reticulatosphaera actinocoronata by Brinkhuis and Biffi (1993) from the Rupelian of Italy. We consider that the difference between such specimens and typical Reticulatosphaera actinocoronata represents a qualitative step forward in a morphological transition which, together with its biostratigraphical applicability, argues for the erection of a new species. An additional, potentially diagnostic feature of Reticulatosphera valdereticulata is its smaller average central
body size compared to that of Reticulatosphaera actinocoronata, which occasionally results in specimens with processes emerging extremely close to each other (Plate 3, figures 4 and 9).
Reticulatosphaera valdereticulata is also somewhat similar to species of Nematosphaeropsis. However, the trabecular network of the latter consists of pairs of trabeculae running parallel to parasutural features, giving rise to a systematically organised network (Wrenn 1988). Moreover, Nematosphaeropsis possesses gonal (and sometimes also intergonal) processes. By contrast, the trabecular network of Reticulatosphaera valdereticulata is made up of more randomly organised single trabeculae, and supporting processes are intratabular.
Eatonicysta ursulae also possesses solid processes that support a dense reticulum (Stover and Evitt 1978). However, the archaeopyle in Eatonicysta ursulae is apical and the processes are flexible, which often results in specimens with preserved flexed processes. Processes in Reticulatosphaera valdereticulata are typically rigid, barely ever observed flexed.