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Apectodinium summissum
Apectodinium summissum, (Harland, 1979), Lentin and Williams, 1981
Originally Wetzeliella subgen. Apectodinium, subsequently (and now) Apectodinium.
Holotype: Harland, 1979, pl.1, fig.12
Locus typicus: North Sea Basin
Stratum typicum: Late Paleocene
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Original description as Wetzeliella (Apectodinium) summissa: [Harland, 1979, p. 66-67]:
Diagnosis:
Small sub-pentagonal cyst having two wall layers fairly closely adpressed except at the apex and sometimes in the lateral areas. Apical horn usually prominent; all other horns absent, incipient, or very poorly developed. Processes -randomly developed, some sutural, hollow slender to flexuous, may be branched, distally evexate, bulbous and opening distally with a small pore. Cingulm planar outlined by sutural processes. Archeopyle [I2a/I2a], ?reduced.
Description:
Cyst compressed dorso-ventrally, the two wall layers thin and the endophragm often crumpled, the endophragm always smooth but the periphragm may be smooth, micro-reticulate or microgranulate, with the ornamentation present on the processes. A periceol always developed in the apex and sometimes laterally according to the prominence of any lateral incipient horns. If no lateral structures are apparent the cyst can assume a more rounded ambitus. The processes appear randomly distributed but some are clearly sutural. Sutural process outline the planar, non-indented, cingulum. Processes composed of periphragm, tapering, distally evexate, sometimes with a distal pore; some have a bulbous tip, many branched. Process length very variable from 1/10 to 1/4 of the cyst diameter. A larger process, often branched, may occupy the site of the left antapical horn.
Variation: Intraspecific variation confined to overall shape and process length, and linked to the former by the incipient development of lateral horns.
Affinities/Discussion:
This form represents an initial morphological step from W. (A.) homomorpha towards W. (A.) quinquelata and ultimately W. (W.) articuleta. It is a distinct form that can be recognized in Palaeocene sediments, and is characterized by its usually prominent apical horn and sub-pentagonal ambitus.
Dimensions:
Holotype: Length, excluding apical horn, 58.75 µm; breadth 55.00 µm.
Range: Length, excluding apical horn, 48.75 (53.96) 57.5 µm breadth 45.0 (50.0) 52.50 µm. Six specimens measured.
Originally Wetzeliella subgen. Apectodinium, subsequently (and now) Apectodinium.
Holotype: Harland, 1979, pl.1, fig.12
Locus typicus: North Sea Basin
Stratum typicum: Late Paleocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Wetzeliella (Apectodinium) summissa: [Harland, 1979, p. 66-67]:
Diagnosis:
Small sub-pentagonal cyst having two wall layers fairly closely adpressed except at the apex and sometimes in the lateral areas. Apical horn usually prominent; all other horns absent, incipient, or very poorly developed. Processes -randomly developed, some sutural, hollow slender to flexuous, may be branched, distally evexate, bulbous and opening distally with a small pore. Cingulm planar outlined by sutural processes. Archeopyle [I2a/I2a], ?reduced.
Description:
Cyst compressed dorso-ventrally, the two wall layers thin and the endophragm often crumpled, the endophragm always smooth but the periphragm may be smooth, micro-reticulate or microgranulate, with the ornamentation present on the processes. A periceol always developed in the apex and sometimes laterally according to the prominence of any lateral incipient horns. If no lateral structures are apparent the cyst can assume a more rounded ambitus. The processes appear randomly distributed but some are clearly sutural. Sutural process outline the planar, non-indented, cingulum. Processes composed of periphragm, tapering, distally evexate, sometimes with a distal pore; some have a bulbous tip, many branched. Process length very variable from 1/10 to 1/4 of the cyst diameter. A larger process, often branched, may occupy the site of the left antapical horn.
Variation: Intraspecific variation confined to overall shape and process length, and linked to the former by the incipient development of lateral horns.
Affinities/Discussion:
This form represents an initial morphological step from W. (A.) homomorpha towards W. (A.) quinquelata and ultimately W. (W.) articuleta. It is a distinct form that can be recognized in Palaeocene sediments, and is characterized by its usually prominent apical horn and sub-pentagonal ambitus.
Dimensions:
Holotype: Length, excluding apical horn, 58.75 µm; breadth 55.00 µm.
Range: Length, excluding apical horn, 48.75 (53.96) 57.5 µm breadth 45.0 (50.0) 52.50 µm. Six specimens measured.