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Dichadogonyaulax sellwoodii
Dichadogonyaulax sellwoodii Sarjeant, 1975
Originally (and now) Dichadogonyaulax, subsequently Ctenidodinium. Lentin and Williams (1993, p.179) retained this species in Dichadogonyaulax.
Stover and Evitt, 1978, transferred this species to Ctenidodinium Deflandre, 1938. Woollam, 1983, retained it in Dichadogonyaulax. Benson, 1985, and Dodekova, 1990, retained the species in Ctenidodinium. Lentin and williams, 1993, followed Sarjeant in Lentin and Williams, 1989, who considered this species to be assignable to Dichadogonyaulax.
Taxonomic junior synonym: Dichadogonyaulax stauromatos, according to Riley and Fenton (1982, p.199) and Lentin and Williams (1993, p.179-180).
Holotype: Sarjeant, 1975, pl.1, figs.A-B, pl.2, figs.I-K
Locus typicus: foreshore exposure, Duntulm, Isle of Skye, west Scotland
Stratum typicum: Lower Ostrea Beds, Jurassic; Bathonian (pre-Discus Zone).
Age: Bathonian
Diagnosis: Sarjeant 1975, p. 52-55: Dichadogonyaulax sellwoodii
A species of Dichadogonyaulax of spheroidal to broadly ovoidal shape, with epitract and hypotract of almost equal size. Apical horn so low and poorly marked as to be visible only in the most favourable orientations, formed by a single pre-apical plate or a group of very tiny pre-apical plates. Sutures between plate-areas marked by low ridges, most often bearing lines of fine spinelets. Tabulation 5", la (on dorsal surface), lav, 6", 6c, 6""", 1p, 1pv, 1"""", plus at least 3 sulcal plates (as, ms, ps) and at least one pre-apical plate. Plate 1"" is especially large. The cingulum forms a weak laevorotatory spiral. Archaeopyle formation occurs by schism along the cingulum; the two hemicysts may survive intact or may break up into their component plate-areas, the apical group of plates typically remaining together. Surface of cyst finely to coarsely granular.
Description. Sarjeant 1975, p. 52-55: Dichadogonyaulax sellwoodii
The inconspicuous apical prominence, so meagre as to scarcely merit the name "horn", is of roughly triangular shape and appears to form from a single small plate, here designated a "pre-apical" plate. The apical plates are of very variable size. Plate 1" is small and polygonal, situated immediately ventrally to the horn and separated from the sulcus by a larger, quadrangular anterior ventral plate. Apical plate 2" is also relatively small, apical plates 3"-5" much larger. A small lozenge-shaped plate is situated between apical plates 3" and 4" and precingular plates 3"" and 4""; it is here provisionally termed intercalary plate la (though, since plates thus designated are usually situated on the ventral surface to the right of the cingulum, this is arguably inappropriate). Plate 6"" is the smallest of the six precingular plates.
The cingulum is occupied by six plates of which the first, plate Ic, is the smallest. Three plates appear to form the sulcus; one of them (as) typically remains attached to the apical plates if the epitract breaks up, the other two (ms and ps) forming part of the hypotract. The posterior sulcal plate (ps) is separated from the antapex by the small, rectangular posterior ventral plate (1pv).
The antapical plate, roughly rectangular in shape, is much the largest plate of the hypotract. Postcingular plates 1""" and 2" are separated from it by the single posterior intercalary plate; both are small. Plate 6""" is also relatively small, plates 3""" to 4""" much larger and of almost equal size.
Detached hypotracts, complete or lacking one or more of their constituent plates, are most frequently encountered. Cysts in which schism is beginning or almost complete are also regularly encountered; in some cases, detached hemicysts or a hypotract and a broken-up epitract were found still in close juxtaposition, suggesting that they separated only during mounting. Detached epitracts proved relatively rare and were frequently distorted, making their study extremely difficult.
The crest spines are most often quite short, but show a considerable variation in length. Pl. 3 Figs. P-Q show a form with especially long spines; the cyst is small (length 44 Á, breadth 40 Á), the spine length (6 Á) almost one-seventh of the cyst length. Such forms might readily be misinterpreted as representing a distinct species.
A few forms with thicker shell walls and low crests were seen. These may be variants of D. sellwoodii or may be representatives of a distinct species. Unfortunately their tabulation could in no case be determined in detail.
Dimensions. Holotype: maximum diameter 50Á .Paratype a.: maximum diameter 42Á Paratype b.: maximum diameter 50Á, spines up to 5Á in length. Paratype c.: length 26Á breadth 44 Á. Paratype d.: measurements not meaningful. Range of dimensions. Overall length 44-82 Á, breadth (diameter) 40-70Á. Material. 76 specimens examined in detail; over 400 complete specimens or hemicysts and a great quantity of fragmental cysts seen.
Remarks: Sarjeant 1975, p. 52-55
Dichadogonyaulax sellwoodii differs from D. norrisii (Pocock, 1972) in the much greater size of plate 1 , in the absence of ridges paralleling plate-area boundaries, in the detail of apical tabulation and, in the presence of six postcingular plates and of a posterior intercalary plate (though it should be noted that Pocock found difficulty in determining the hypotractal tabulation of his species). It differs from D. schizoblata (Norris, 1965) in the details of apical and ventral tabulation and the character of the crests. The other species hitherto described exhibit even more marked differences from this species in tabulation and crest character.
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Poulsen, 1996, p. 66
Dichadogonyaulax sellwoodii Group of Woollam & Riding 1983
Pl. 15, Fig. 6
Remarks. This group includes forms attributable to D. sellwoodii and Ctenidodinium? stauromatos and related forms, which often are damaged because of fairly thin walls.
Recorded occurrence. Denmark: Trichodinium scarburghense Zone.
Originally (and now) Dichadogonyaulax, subsequently Ctenidodinium. Lentin and Williams (1993, p.179) retained this species in Dichadogonyaulax.
Stover and Evitt, 1978, transferred this species to Ctenidodinium Deflandre, 1938. Woollam, 1983, retained it in Dichadogonyaulax. Benson, 1985, and Dodekova, 1990, retained the species in Ctenidodinium. Lentin and williams, 1993, followed Sarjeant in Lentin and Williams, 1989, who considered this species to be assignable to Dichadogonyaulax.
Taxonomic junior synonym: Dichadogonyaulax stauromatos, according to Riley and Fenton (1982, p.199) and Lentin and Williams (1993, p.179-180).
Holotype: Sarjeant, 1975, pl.1, figs.A-B, pl.2, figs.I-K
Locus typicus: foreshore exposure, Duntulm, Isle of Skye, west Scotland
Stratum typicum: Lower Ostrea Beds, Jurassic; Bathonian (pre-Discus Zone).
Age: Bathonian
Diagnosis: Sarjeant 1975, p. 52-55: Dichadogonyaulax sellwoodii
A species of Dichadogonyaulax of spheroidal to broadly ovoidal shape, with epitract and hypotract of almost equal size. Apical horn so low and poorly marked as to be visible only in the most favourable orientations, formed by a single pre-apical plate or a group of very tiny pre-apical plates. Sutures between plate-areas marked by low ridges, most often bearing lines of fine spinelets. Tabulation 5", la (on dorsal surface), lav, 6", 6c, 6""", 1p, 1pv, 1"""", plus at least 3 sulcal plates (as, ms, ps) and at least one pre-apical plate. Plate 1"" is especially large. The cingulum forms a weak laevorotatory spiral. Archaeopyle formation occurs by schism along the cingulum; the two hemicysts may survive intact or may break up into their component plate-areas, the apical group of plates typically remaining together. Surface of cyst finely to coarsely granular.
Description. Sarjeant 1975, p. 52-55: Dichadogonyaulax sellwoodii
The inconspicuous apical prominence, so meagre as to scarcely merit the name "horn", is of roughly triangular shape and appears to form from a single small plate, here designated a "pre-apical" plate. The apical plates are of very variable size. Plate 1" is small and polygonal, situated immediately ventrally to the horn and separated from the sulcus by a larger, quadrangular anterior ventral plate. Apical plate 2" is also relatively small, apical plates 3"-5" much larger. A small lozenge-shaped plate is situated between apical plates 3" and 4" and precingular plates 3"" and 4""; it is here provisionally termed intercalary plate la (though, since plates thus designated are usually situated on the ventral surface to the right of the cingulum, this is arguably inappropriate). Plate 6"" is the smallest of the six precingular plates.
The cingulum is occupied by six plates of which the first, plate Ic, is the smallest. Three plates appear to form the sulcus; one of them (as) typically remains attached to the apical plates if the epitract breaks up, the other two (ms and ps) forming part of the hypotract. The posterior sulcal plate (ps) is separated from the antapex by the small, rectangular posterior ventral plate (1pv).
The antapical plate, roughly rectangular in shape, is much the largest plate of the hypotract. Postcingular plates 1""" and 2" are separated from it by the single posterior intercalary plate; both are small. Plate 6""" is also relatively small, plates 3""" to 4""" much larger and of almost equal size.
Detached hypotracts, complete or lacking one or more of their constituent plates, are most frequently encountered. Cysts in which schism is beginning or almost complete are also regularly encountered; in some cases, detached hemicysts or a hypotract and a broken-up epitract were found still in close juxtaposition, suggesting that they separated only during mounting. Detached epitracts proved relatively rare and were frequently distorted, making their study extremely difficult.
The crest spines are most often quite short, but show a considerable variation in length. Pl. 3 Figs. P-Q show a form with especially long spines; the cyst is small (length 44 Á, breadth 40 Á), the spine length (6 Á) almost one-seventh of the cyst length. Such forms might readily be misinterpreted as representing a distinct species.
A few forms with thicker shell walls and low crests were seen. These may be variants of D. sellwoodii or may be representatives of a distinct species. Unfortunately their tabulation could in no case be determined in detail.
Dimensions. Holotype: maximum diameter 50Á .Paratype a.: maximum diameter 42Á Paratype b.: maximum diameter 50Á, spines up to 5Á in length. Paratype c.: length 26Á breadth 44 Á. Paratype d.: measurements not meaningful. Range of dimensions. Overall length 44-82 Á, breadth (diameter) 40-70Á. Material. 76 specimens examined in detail; over 400 complete specimens or hemicysts and a great quantity of fragmental cysts seen.
Remarks: Sarjeant 1975, p. 52-55
Dichadogonyaulax sellwoodii differs from D. norrisii (Pocock, 1972) in the much greater size of plate 1 , in the absence of ridges paralleling plate-area boundaries, in the detail of apical tabulation and, in the presence of six postcingular plates and of a posterior intercalary plate (though it should be noted that Pocock found difficulty in determining the hypotractal tabulation of his species). It differs from D. schizoblata (Norris, 1965) in the details of apical and ventral tabulation and the character of the crests. The other species hitherto described exhibit even more marked differences from this species in tabulation and crest character.
---------------------------------
Poulsen, 1996, p. 66
Dichadogonyaulax sellwoodii Group of Woollam & Riding 1983
Pl. 15, Fig. 6
Remarks. This group includes forms attributable to D. sellwoodii and Ctenidodinium? stauromatos and related forms, which often are damaged because of fairly thin walls.
Recorded occurrence. Denmark: Trichodinium scarburghense Zone.