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Oligosphaeridium anapetum
Oligosphaeridium anapetum van Mourik et al., 2001, p.241,243, figs.8a–e.
Holotype: van Mourik et al., 2001, figs.8a–c.
Age: late middle-late Eocene.
Original description (Van Mourik et al., 2001)
Etymology Greek 'anapetos', meaning wide open, expanded.
HolotypeSlide I, 1053A-20X-5, 72-75/I (P44). Fig. 8a-c.
Diagnosis. A species of Oligosphaeridium with tubiform processes whose walls may be perforate or incomplete towards the cingulum and which proximally form an annulate to arcuate contact with the cyst body.
Description Shape. Body subspherical. Wall relationships. Endophragm and periphragm in contact except where periphragm forms the processes. Wall features. Processes intratabular, tubiform to cylindrical, striate, one per paraplate, absent on cingulum and some of sulcus. Processes open distally, expanded, with undulose to slightly
serrate margins. Some processes perforated along their length or may be incomplete towards the cingulum, so that proximally the process contact with the cyst body is arcuate rather than annulate. Process width reflects location, with 2" and 4' being the broadest. Occasionally there is an adventitious process on the hypocyst. Periphragm between processes smooth to scabrate. Paratabulation. Indicated by intratabular processes, gonyaulacacean, process formula: 6", 5-6'", 4", lp, 1", 0-Is. Archeopyle. Apical, principal archeopyle suture zigzag, presumably reflecting four apical paraplates. Operculum free, with four processes 1' and 3' of approximately equal size, 4' and 1' slender. Paracingulum. Indicated by absence of processes and orientation of arcuate process bases. Parasulcus. Indicated by one process, the posterior sulcal or devoid of processes. Size Main body. Length 80 lam; width, 52-64 µm. Processes. Length, 9-24 µm, width, 3-19 µm (n = 7).
Type locality. ODP Site 1053A, 166.64 mbsf, 172.16 msbf, and 174.72 msbf, Blake Nose, offshore from Florida.
Stratigraphic range. Upper middle to upper Eocene sequence.
Comparison. The most distinctive feature of Oligosphaeridium anapetum is the structure of the processes. These are striate, whereas all other species of the genus have processes with smooth walls. Some of the precingular and postcingular processes are also unusual in not being truly tubiform; rather that part of the process towards
the cingulum is open. This is reminiscent of the type or ornamentation found in Hemiplacophora semilunifera. The variability in the number of postcingular, from five to six, and sulcal processes, none to one, plus the occasional presence of an adventitious process on the hypocyst also differentiate this species from other species of
Oligosphaeridium.
Holotype: van Mourik et al., 2001, figs.8a–c.
Age: late middle-late Eocene.
Original description (Van Mourik et al., 2001)
Etymology Greek 'anapetos', meaning wide open, expanded.
HolotypeSlide I, 1053A-20X-5, 72-75/I (P44). Fig. 8a-c.
Diagnosis. A species of Oligosphaeridium with tubiform processes whose walls may be perforate or incomplete towards the cingulum and which proximally form an annulate to arcuate contact with the cyst body.
Description Shape. Body subspherical. Wall relationships. Endophragm and periphragm in contact except where periphragm forms the processes. Wall features. Processes intratabular, tubiform to cylindrical, striate, one per paraplate, absent on cingulum and some of sulcus. Processes open distally, expanded, with undulose to slightly
serrate margins. Some processes perforated along their length or may be incomplete towards the cingulum, so that proximally the process contact with the cyst body is arcuate rather than annulate. Process width reflects location, with 2" and 4' being the broadest. Occasionally there is an adventitious process on the hypocyst. Periphragm between processes smooth to scabrate. Paratabulation. Indicated by intratabular processes, gonyaulacacean, process formula: 6", 5-6'", 4", lp, 1", 0-Is. Archeopyle. Apical, principal archeopyle suture zigzag, presumably reflecting four apical paraplates. Operculum free, with four processes 1' and 3' of approximately equal size, 4' and 1' slender. Paracingulum. Indicated by absence of processes and orientation of arcuate process bases. Parasulcus. Indicated by one process, the posterior sulcal or devoid of processes. Size Main body. Length 80 lam; width, 52-64 µm. Processes. Length, 9-24 µm, width, 3-19 µm (n = 7).
Type locality. ODP Site 1053A, 166.64 mbsf, 172.16 msbf, and 174.72 msbf, Blake Nose, offshore from Florida.
Stratigraphic range. Upper middle to upper Eocene sequence.
Comparison. The most distinctive feature of Oligosphaeridium anapetum is the structure of the processes. These are striate, whereas all other species of the genus have processes with smooth walls. Some of the precingular and postcingular processes are also unusual in not being truly tubiform; rather that part of the process towards
the cingulum is open. This is reminiscent of the type or ornamentation found in Hemiplacophora semilunifera. The variability in the number of postcingular, from five to six, and sulcal processes, none to one, plus the occasional presence of an adventitious process on the hypocyst also differentiate this species from other species of
Oligosphaeridium.