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Valvaeodinium hymenosynypha
Valvaeodinium hymenosynypha, (Morbey, 1975) comb. nov., Lindström, S., 2023, p. 5-7
Holotype: Morbey, 1975, in Palaeontographica Abteilung B. 152: pl. 19, figs 2–4
Type locality: United Kingdom: Rhaetian, Westbury Formation, Bunny Hill Borehole, Nottinghamshire (Morbey and Neves 1974; Morbey 1975).
Local stratigraphic range: United Kingdom: Rhaetian; Denmark: late Rhaetian to earliest Hettangian; Austria: latest Rhaetian
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Description: Lindström, S., 2023:
Diagnosis:
A proximate, holocavate dinoflagellate cyst with a small ellipsoidal to rounded body with a two-layered wall.
The autophragm appears to be slightly thicker than or of the same thickness as the ectophragm. The two wall layers are separated by membraneous structures forming a reticulate pattern with fine to medium-sized meshes.
Partial paratabulation is discernable on some specimens, e.g. in Plate 1, figures 2 and 4 and Plate 2, figure 14, and seems to indicate typical Valvaeodinium paratabulation 4', 1a, 5''–6'', 6c, 5''', 1'''' according to Below (1987); however, the reticulate structure of the wall hinders full reconstruction.
The archaeopyle is a combination type tAtI formed by all (or only three?) apical plates plus the intercalary plate, leaving a characteristic zigzag pattern indicating 5''–6''. In many specimens these apical plates are still at least partially attached.
Dimensions:
Length: 23 (28) 35µm; width: 19 (23) 30µm (16 specimens, this paper). Length: 17 (23) 30µm (50 specimens, Morbey 1975).
Remarks:
Morbey (1975, pl. 19, figs 2–4 therein) originally described this species as Cymatiosphaera hymenosynypha, a prasinophyte, although he did remark that it displayed apical ruptures similar to those of some chorate dinoflagellate cysts with apical archaeopyles. Identical specimens to those described by Morbey (1975) were also reported from the Westbury Formation of the Bunny Hill borehole in Nottinghamshire by Morbey and Neves (1974, pl. II, figs 8 and 9 therein).
Affinities/Comparison:
Two other cavate Valvaeodinium species are known from the Early to Middle Jurassic, namely Valvaeodinium cavum and Valvaeodinium hanneae, from the Toarcian–Bajocian and latest Bathonian–earliest Callovian, respectively (Figure 1). Valvaeodinium cavum differs from Valvaeodinium hymenosy-nypha (Morbey) comb. nov. in that the ecto- and autophragm are separated by trabeculae, and in its larger size and more sphaeroidal shape (Davies 1983; Below 1987). Valvaeodinium hanneae, on the other hand, is more similar in shape and ornamentation to Valvaeodinium hymenosynypha; however, the former is larger in size and the two wall layers are separated by vermiculae forming an irregular and incomplete reticulum (Piasecki 2001) while in Valvaeodinium hymenosynypha the reticulum is more regular and well developed (Figure 1; Table 1).
Holotype: Morbey, 1975, in Palaeontographica Abteilung B. 152: pl. 19, figs 2–4
Type locality: United Kingdom: Rhaetian, Westbury Formation, Bunny Hill Borehole, Nottinghamshire (Morbey and Neves 1974; Morbey 1975).
Local stratigraphic range: United Kingdom: Rhaetian; Denmark: late Rhaetian to earliest Hettangian; Austria: latest Rhaetian
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Description: Lindström, S., 2023:
Diagnosis:
A proximate, holocavate dinoflagellate cyst with a small ellipsoidal to rounded body with a two-layered wall.
The autophragm appears to be slightly thicker than or of the same thickness as the ectophragm. The two wall layers are separated by membraneous structures forming a reticulate pattern with fine to medium-sized meshes.
Partial paratabulation is discernable on some specimens, e.g. in Plate 1, figures 2 and 4 and Plate 2, figure 14, and seems to indicate typical Valvaeodinium paratabulation 4', 1a, 5''–6'', 6c, 5''', 1'''' according to Below (1987); however, the reticulate structure of the wall hinders full reconstruction.
The archaeopyle is a combination type tAtI formed by all (or only three?) apical plates plus the intercalary plate, leaving a characteristic zigzag pattern indicating 5''–6''. In many specimens these apical plates are still at least partially attached.
Dimensions:
Length: 23 (28) 35µm; width: 19 (23) 30µm (16 specimens, this paper). Length: 17 (23) 30µm (50 specimens, Morbey 1975).
Remarks:
Morbey (1975, pl. 19, figs 2–4 therein) originally described this species as Cymatiosphaera hymenosynypha, a prasinophyte, although he did remark that it displayed apical ruptures similar to those of some chorate dinoflagellate cysts with apical archaeopyles. Identical specimens to those described by Morbey (1975) were also reported from the Westbury Formation of the Bunny Hill borehole in Nottinghamshire by Morbey and Neves (1974, pl. II, figs 8 and 9 therein).
Affinities/Comparison:
Two other cavate Valvaeodinium species are known from the Early to Middle Jurassic, namely Valvaeodinium cavum and Valvaeodinium hanneae, from the Toarcian–Bajocian and latest Bathonian–earliest Callovian, respectively (Figure 1). Valvaeodinium cavum differs from Valvaeodinium hymenosy-nypha (Morbey) comb. nov. in that the ecto- and autophragm are separated by trabeculae, and in its larger size and more sphaeroidal shape (Davies 1983; Below 1987). Valvaeodinium hanneae, on the other hand, is more similar in shape and ornamentation to Valvaeodinium hymenosynypha; however, the former is larger in size and the two wall layers are separated by vermiculae forming an irregular and incomplete reticulum (Piasecki 2001) while in Valvaeodinium hymenosynypha the reticulum is more regular and well developed (Figure 1; Table 1).