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Apteodinium mutabile
From Fensome et al., 2019:
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Original description Duxbury, 2019
Holotype: Plate 14, Figure 5
Paratype: Plate 14, Figures 11, 12
Type Locality: Heslerton No. 2 at 26.00 m (core chip), late
Barremian age. Holotype: E.F. T37.4. Paratype: E.F. T27.1
Derivation of Name: From the Latin mutabilis, changeable - in reference to the variability in morphology of this species.
Diagnosis: A thin-walled, ovoidal to ellipsoidal species, autophragm only, with a smooth to rarely microrugulate surface and a prominent apical horn. The horn is biform, consisting of a hollow, distally-closed elongation of the main cyst, surmounted by a short spike or relatively broad, flexible extension. Conspicuous folds cover the surface of the cyst and these are frequently developed into prominent outgrowths, particularly on the hypocyst. The form and number of outgrowths varies markedly between specimens. Archeopyle single plate precingular (3'').
Dimensions (including outgrowths): Holotype: Length - 89 μm.
Width - 58μm. Paratype: Length - 68 μm. Width - 73 μm.
Overall: 91 (77) 68 μm × 73 (60) 53 μm.
Specimens Measured: 5.
Remarks: This is a rare and unusual species exhibiting a wide morphological range, from relatively simple specimens (Plate 14, Figure 1) limited to surficial folds to specimens with several prominent outgrowths (Plate 14, Figures 11, 12), particularly on the hypocyst. Complex specimens can be reminiscent of the pareodiniacean Cantulodinium speciosum Alberti 1961, but differ in having a single plate (3'') archeopyle, as opposed to the intercalary archeopyle of C. speciosum. The dimensions of this species vary significantly and relate directly to the degree and locations of outgrowth development. Despite the sometimes complex morphology, there appears to be only a single cyst wall.
Apteodinium mutabile was restricted to the late Barremian, occurring between 26.00 m and 20.00 m in Heslerton No. 2 (more extreme specimens between 26.00 m and 22.95 m), and possibly encompasses specimens illustrated by Alberti (1961, Plate 4, Figures 4–6) as Apteodinium granulatum, also from the late Barremian. Sarjeant (1985, p. 83) included one of Alberti’s specimens (Alberti 1961, Plate 4, Figure 5) within Apteodinium thelium Sarjeant 1985, but this is rejected here. Although the age range of A. thelium quoted by Sarjeant is late Barremian to late Aptian, this appears to be only because of the inclusion of Alberti’s specimen; all of Sarjeant’s (op. cit.) type material for A. thelium is from the late Aptian.
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Original description Duxbury, 2019
Holotype: Plate 14, Figure 5
Paratype: Plate 14, Figures 11, 12
Type Locality: Heslerton No. 2 at 26.00 m (core chip), late
Barremian age. Holotype: E.F. T37.4. Paratype: E.F. T27.1
Derivation of Name: From the Latin mutabilis, changeable - in reference to the variability in morphology of this species.
Diagnosis: A thin-walled, ovoidal to ellipsoidal species, autophragm only, with a smooth to rarely microrugulate surface and a prominent apical horn. The horn is biform, consisting of a hollow, distally-closed elongation of the main cyst, surmounted by a short spike or relatively broad, flexible extension. Conspicuous folds cover the surface of the cyst and these are frequently developed into prominent outgrowths, particularly on the hypocyst. The form and number of outgrowths varies markedly between specimens. Archeopyle single plate precingular (3'').
Dimensions (including outgrowths): Holotype: Length - 89 μm.
Width - 58μm. Paratype: Length - 68 μm. Width - 73 μm.
Overall: 91 (77) 68 μm × 73 (60) 53 μm.
Specimens Measured: 5.
Remarks: This is a rare and unusual species exhibiting a wide morphological range, from relatively simple specimens (Plate 14, Figure 1) limited to surficial folds to specimens with several prominent outgrowths (Plate 14, Figures 11, 12), particularly on the hypocyst. Complex specimens can be reminiscent of the pareodiniacean Cantulodinium speciosum Alberti 1961, but differ in having a single plate (3'') archeopyle, as opposed to the intercalary archeopyle of C. speciosum. The dimensions of this species vary significantly and relate directly to the degree and locations of outgrowth development. Despite the sometimes complex morphology, there appears to be only a single cyst wall.
Apteodinium mutabile was restricted to the late Barremian, occurring between 26.00 m and 20.00 m in Heslerton No. 2 (more extreme specimens between 26.00 m and 22.95 m), and possibly encompasses specimens illustrated by Alberti (1961, Plate 4, Figures 4–6) as Apteodinium granulatum, also from the late Barremian. Sarjeant (1985, p. 83) included one of Alberti’s specimens (Alberti 1961, Plate 4, Figure 5) within Apteodinium thelium Sarjeant 1985, but this is rejected here. Although the age range of A. thelium quoted by Sarjeant is late Barremian to late Aptian, this appears to be only because of the inclusion of Alberti’s specimen; all of Sarjeant’s (op. cit.) type material for A. thelium is from the late Aptian.