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Meiourogonyaulax stoveri ssp. inflata
Plate 12, Figures 8, 11, 14, 17
Holotype: Plate 12, Figure 8.
Paratype: Plate 12, Figures 14, 17.
Type Locality: Speeton Bed C4C, late Hauterivian, gottschei ammonite Zone. Holotype: Slide C4C(5), E.F. J30.0. Paratype: Slide C4C(3), E.F. C44.0.
Derivation of Name: From the Latin inflatus, puffed up, swollen- in reference to the cavation demonstrated by this subspecies.
Diagnosis: An intermediate to large, thick-walled subspecies, subcircular to pentagonal in outline, smooth or with scabrate to microreticulate ornament. Tabulation of the formula ?', 6'', ?c, 6''', 1p, 1p.v., 1'''' is marked by distally entire crests which are higher on the hypocyst and particularly prominent towards the antapex. Suturocavation is well-developed at the apex, antapex and marginally, and a few large holes can be present towards the antapex. The prominent sulcal groove is devoid of ornament. The archeopyle is apical and the zig-zag archeopyle margin displays a distinct but shallow sulcal notch.
Dimensions: Holotype: Length - 101 μm. Width - 89 μm.
Paratype: Length - 96 μm. Width - 94 μm.
Complete specimens (4 recorded): 101 (97) 89 μm × 89 (82) 71 μm.
Overall (operculum lost) - 94 (86) 71 μm × 94 (88) 81 μm.
Specimens Measured: 10.
Remarks: This subspecies is typical of Meiourogonyaulax stoveri in its often subcircular outline, thick wall and crests which are highest towards the antapex. It differs from Millioud’s type material in its significantly greater size (complete specimens about 20% larger) and in the extreme suturocavation, particularly at the apex, antapex and marginally, so that this taxon can become marginocavate and resemble species of Senoniasphaera Clarke and Verdier 1967.
In some respects, particularly its relatively large size, Meiourogonyaulax stoveri subsp. inflata resembles Meiourogonyaulax stoveri subsp. grandis Duxbury 2019 but differs in being much less ornate, in the high degree of suturocavation (although some suturocavation can occur in M. stoveri subsp. grandis), in its often circular ambitus and in the large holes which can develop towards the antapex.
Meiourogonyaulax stoveri subsp. inflata may also be compared with Meiourogonyaulax pertusa subsp. heta Below 1981, a significantly smaller taxon (range quoted by Below: Length - 90(76)72 μm; Width - 78(69)60 μm). In transmitted light, the latter taxon appears to have densely and variably perforate sutural crests, although Below’s SEM work proved a smooth surface, suggesting that these “supposed perforations of the periphragm really represent endophragmal reticulation in the lumen between the two cyst membranes” (translation from Below 1981, p. 57). This subspecies was restricted to Speeton Beds C4C and C3, late Hauterivian, gottschei to marginatus ammonite Zones, whereas specimens assigned to M. stoveri subsp. stoveri were observed throughout.
Holotype: Plate 12, Figure 8.
Paratype: Plate 12, Figures 14, 17.
Type Locality: Speeton Bed C4C, late Hauterivian, gottschei ammonite Zone. Holotype: Slide C4C(5), E.F. J30.0. Paratype: Slide C4C(3), E.F. C44.0.
Derivation of Name: From the Latin inflatus, puffed up, swollen- in reference to the cavation demonstrated by this subspecies.
Diagnosis: An intermediate to large, thick-walled subspecies, subcircular to pentagonal in outline, smooth or with scabrate to microreticulate ornament. Tabulation of the formula ?', 6'', ?c, 6''', 1p, 1p.v., 1'''' is marked by distally entire crests which are higher on the hypocyst and particularly prominent towards the antapex. Suturocavation is well-developed at the apex, antapex and marginally, and a few large holes can be present towards the antapex. The prominent sulcal groove is devoid of ornament. The archeopyle is apical and the zig-zag archeopyle margin displays a distinct but shallow sulcal notch.
Dimensions: Holotype: Length - 101 μm. Width - 89 μm.
Paratype: Length - 96 μm. Width - 94 μm.
Complete specimens (4 recorded): 101 (97) 89 μm × 89 (82) 71 μm.
Overall (operculum lost) - 94 (86) 71 μm × 94 (88) 81 μm.
Specimens Measured: 10.
Remarks: This subspecies is typical of Meiourogonyaulax stoveri in its often subcircular outline, thick wall and crests which are highest towards the antapex. It differs from Millioud’s type material in its significantly greater size (complete specimens about 20% larger) and in the extreme suturocavation, particularly at the apex, antapex and marginally, so that this taxon can become marginocavate and resemble species of Senoniasphaera Clarke and Verdier 1967.
In some respects, particularly its relatively large size, Meiourogonyaulax stoveri subsp. inflata resembles Meiourogonyaulax stoveri subsp. grandis Duxbury 2019 but differs in being much less ornate, in the high degree of suturocavation (although some suturocavation can occur in M. stoveri subsp. grandis), in its often circular ambitus and in the large holes which can develop towards the antapex.
Meiourogonyaulax stoveri subsp. inflata may also be compared with Meiourogonyaulax pertusa subsp. heta Below 1981, a significantly smaller taxon (range quoted by Below: Length - 90(76)72 μm; Width - 78(69)60 μm). In transmitted light, the latter taxon appears to have densely and variably perforate sutural crests, although Below’s SEM work proved a smooth surface, suggesting that these “supposed perforations of the periphragm really represent endophragmal reticulation in the lumen between the two cyst membranes” (translation from Below 1981, p. 57). This subspecies was restricted to Speeton Beds C4C and C3, late Hauterivian, gottschei to marginatus ammonite Zones, whereas specimens assigned to M. stoveri subsp. stoveri were observed throughout.