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Suessia cristata
Suessia cristata sp. nov., Mantle et al. 2020, p. 27 - 33
Holotype: Mantle et al. 2020, Plate IV, 13a, b
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (early Norian, Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small to medium, proximate to proximochorate, biconical, ovoidal, or subspherical, acavate dinoflagellate cysts. The hypocyst is slightly larger than the epicyst. Only a single, moderately thin granulate, microreticulate, or scabrate wall layer (autophragm) is present. The suessioid tabulation is expressed by low sutural ridges that are commonly surmounted by thin membranous crests, 2–5 μm high. These strongly perforate crests may be partly or strongly distally spinate, generally increase in prominence on the hypocyst and are absent apically. The folded and thin nature of these crests obscures the full tabulation, but this appears to involve seven to nine latitudinal plate series.
Tabulation formula (sensu Below, 1987): xn 3 , xn 2 , xn a , 8–12n 1 , 10+c, xn1, xn2, xn3, 2–3n4
Tabulation formula (sensu Morbey, 1975): x′, xa, xap, 8–12′′, 10+c, x′′′, xp, xpa, 2–3′′′′
Archaeopyle: commonly formed through the loss of 3–8 anterior intercalary and postapical plates, though rarely, it may also involve the loss of all the climactal plates.
Operculum: compound, forms via the loss of individual plates or occasionally a small cluster of two or three plates
Dimensions:
Overall length (including apical plates) 44 μm (48 μm) 52 μm; maximum width 36 μm (41 μm) 48 μm.
10 measured specimens
Remarks:
It is possible that the study of further well-preserved specimens may reveal forms with more than 12 precingular plates.
Suessia swabiana was originally described by Morbey (1975) as being “pseudocavate” with a periphragm that may be partially detached apically or equatorially. Below (1987) confirmed the presence of an outer pellicle with a peridiniacean tabulation pattern, thus differing substantially from the tabulation of the inner cyst wall. However, most specimens of Suessia swabiana do not exhibit this outer wall layer. A definite outer pellicle layer is not apparent on Suessia cristata sp. nov., but it may be present on exceptionally preserved specimens.
Affinities/Comparison:
The high, membranous, perforate crests of Suessia cristata sp. nov. readily distinguish it from Suessia swabiana, although these species are probably very closely related. There are no substantial differences in archaeopyle development, size, or tabulation. The distally connected sutural spines of Wanneria misolensis may be broadly similar to the perforate crests of some specimens of Suessia cristata sp. nov. However, the irregular distal edge, often surmounted by short spines, and membranous nature of the crests on Suessia cristata sp. nov. Differ substantially from the well-ordered and thicker bifurcating spines of Wanneria misolensis. The generic differences are also significant; Suessia cristata sp. nov. commonly loses only 3–8 anterior intercalary and postapical plates to form the archaeopyle, whereas Wanneria misolensis loses all the apical, anterior intercalary and postapical plates as a single opercular piece.
Holotype: Mantle et al. 2020, Plate IV, 13a, b
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (early Norian, Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small to medium, proximate to proximochorate, biconical, ovoidal, or subspherical, acavate dinoflagellate cysts. The hypocyst is slightly larger than the epicyst. Only a single, moderately thin granulate, microreticulate, or scabrate wall layer (autophragm) is present. The suessioid tabulation is expressed by low sutural ridges that are commonly surmounted by thin membranous crests, 2–5 μm high. These strongly perforate crests may be partly or strongly distally spinate, generally increase in prominence on the hypocyst and are absent apically. The folded and thin nature of these crests obscures the full tabulation, but this appears to involve seven to nine latitudinal plate series.
Tabulation formula (sensu Below, 1987): xn 3 , xn 2 , xn a , 8–12n 1 , 10+c, xn1, xn2, xn3, 2–3n4
Tabulation formula (sensu Morbey, 1975): x′, xa, xap, 8–12′′, 10+c, x′′′, xp, xpa, 2–3′′′′
Archaeopyle: commonly formed through the loss of 3–8 anterior intercalary and postapical plates, though rarely, it may also involve the loss of all the climactal plates.
Operculum: compound, forms via the loss of individual plates or occasionally a small cluster of two or three plates
Dimensions:
Overall length (including apical plates) 44 μm (48 μm) 52 μm; maximum width 36 μm (41 μm) 48 μm.
10 measured specimens
Remarks:
It is possible that the study of further well-preserved specimens may reveal forms with more than 12 precingular plates.
Suessia swabiana was originally described by Morbey (1975) as being “pseudocavate” with a periphragm that may be partially detached apically or equatorially. Below (1987) confirmed the presence of an outer pellicle with a peridiniacean tabulation pattern, thus differing substantially from the tabulation of the inner cyst wall. However, most specimens of Suessia swabiana do not exhibit this outer wall layer. A definite outer pellicle layer is not apparent on Suessia cristata sp. nov., but it may be present on exceptionally preserved specimens.
Affinities/Comparison:
The high, membranous, perforate crests of Suessia cristata sp. nov. readily distinguish it from Suessia swabiana, although these species are probably very closely related. There are no substantial differences in archaeopyle development, size, or tabulation. The distally connected sutural spines of Wanneria misolensis may be broadly similar to the perforate crests of some specimens of Suessia cristata sp. nov. However, the irregular distal edge, often surmounted by short spines, and membranous nature of the crests on Suessia cristata sp. nov. Differ substantially from the well-ordered and thicker bifurcating spines of Wanneria misolensis. The generic differences are also significant; Suessia cristata sp. nov. commonly loses only 3–8 anterior intercalary and postapical plates to form the archaeopyle, whereas Wanneria misolensis loses all the apical, anterior intercalary and postapical plates as a single opercular piece.