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Frigatadinium
Frigatadinium Riding, 2004, p.237–238.
Type: Riding, 2004, figs.3G–H, as Frigatadinium frigatense.
Original description (Riding, 2004):
Diagnosis. Subangular to ellipsoidal proximate acavate dinoflagella.te cysts intermediate to large in size and dorsoventrally flattened. A small apical horn may be present. The parasutures indicate a sexiform gonyaulacalean paratabulation pattern with clear dextral torsion· the ventral organisation is L-type. The paratabulation formula is ?pr, 4' 6 6c, 6 ' lp I' , ?6s. The paratabula ion is marked by relatively low relief parasutural ornamentation that is best developed in the lateral and dorsal areas. The parasutures on the entral surface are of markedly low relief and may be partially to entirely suppressed. The parasutural ornament where developed is longest in the antapical area and becomes shorter in an apical direction. The paracingulum is lae orotatory and is located equatorially. The parasulcus is relatively wide and i not subdivided. The archaeopyle is single paraplate precingular (type P) and the operculum comprise the rniddorsal paraplate, 3 '' and is free.
Comment. Frigatadinium is a distinctive cribroperidinioid genus that normally has a small apical horn and is fully paratabulate except in the ventral area where the parasutures surrounding the parasulcus are markedly suppressed. Despite the similarities of Frigatadinium to Cribroperidinium Neale & Sarjeant 1962 emend. Helenes 1984, it is this distincti e ventral parasutural suppression and the wide parasulcus which require the erection of a new genus.
Comparison. As stated above Frigatadinium most closely resembles Cribroperidinium. Frigatadinium clearly exhibits dextral torsion i.e. in the postcingular series he 4' /5''' paraplate boundary is close to the centre of the 3'' precingular paraplate (Fig 2, Fensome et al., 1993, fig. 91 ). Dextral torsion is a key feature of the Subfamily Cribroperidinioideae (Fensome et al.1993, Riding & Fensome 2002). Frigatadinium is more elongate and angular in outline than most species of Cribroperidinium whjch is typically ovoidal (Helenes 1984 ). Frigatadinium also normally has a short apical horn that may be composed of ornamentational features. Representatives of Cribroperidinium normally have a prominent apical horn that is consistently formed by autophragm. Frigatadinium also lacks the prominent intratabular ridges/ ornamentation al lineations that are common in Cribroperidinium. However the most characteristic feature of Frigatadinium is the marked suppres ion of the parasutures in the ventral area (Fig. 2). Note that the elongate 1 p paraplate is not defined and the parasutures defining the 1' and 2 paraplates are much reduced. Some species of Cribroperidinium do not exhibit any parasutures within the parasulcus for example Cribroperidinium diaphane (Cookson & Eisenack 195 8 Sto er & Evitt 1978. These forms, bowe er all have clear ''' 2 and 1 p paraplates (Helenes, 1984 pl. 2, fig. 2). A similar phenomenon is present in certain other unrelated genera such as Gonyaulacysta Deflandre 1964 (see Jan du Chene eta!. 1986, pl. 37 figs 9, 14) and Impagidinium Stover & Evitt 1978 (see Jan du Chene et al. 1986 pl. 53 figs 3. 11) however as in Cribroperidinium diaphane, the suppression is not normally as prof ot1nd as in Frigatadinium. Ventral paratabulation is also poorly defined in Cyclonephelium Deflandre & Cookson 1955 and Glaphyrocysta Stover & Evitt 1978. The ventral suppression of parasuture is nevertheless relatively unusual among gonyaulacacean dinoflagellate cysts and the type species Frigatadinium frigatense cannot be readily accommodated in Cribroperidinium, therefore a new genus is required. The relatively wide parasulcus also distinguishes this genus from Cribroperidinium.
Derivation of name. From the Frigate-I well.
Type: Riding, 2004, figs.3G–H, as Frigatadinium frigatense.
Original description (Riding, 2004):
Diagnosis. Subangular to ellipsoidal proximate acavate dinoflagella.te cysts intermediate to large in size and dorsoventrally flattened. A small apical horn may be present. The parasutures indicate a sexiform gonyaulacalean paratabulation pattern with clear dextral torsion· the ventral organisation is L-type. The paratabulation formula is ?pr, 4' 6 6c, 6 ' lp I' , ?6s. The paratabula ion is marked by relatively low relief parasutural ornamentation that is best developed in the lateral and dorsal areas. The parasutures on the entral surface are of markedly low relief and may be partially to entirely suppressed. The parasutural ornament where developed is longest in the antapical area and becomes shorter in an apical direction. The paracingulum is lae orotatory and is located equatorially. The parasulcus is relatively wide and i not subdivided. The archaeopyle is single paraplate precingular (type P) and the operculum comprise the rniddorsal paraplate, 3 '' and is free.
Comment. Frigatadinium is a distinctive cribroperidinioid genus that normally has a small apical horn and is fully paratabulate except in the ventral area where the parasutures surrounding the parasulcus are markedly suppressed. Despite the similarities of Frigatadinium to Cribroperidinium Neale & Sarjeant 1962 emend. Helenes 1984, it is this distincti e ventral parasutural suppression and the wide parasulcus which require the erection of a new genus.
Comparison. As stated above Frigatadinium most closely resembles Cribroperidinium. Frigatadinium clearly exhibits dextral torsion i.e. in the postcingular series he 4' /5''' paraplate boundary is close to the centre of the 3'' precingular paraplate (Fig 2, Fensome et al., 1993, fig. 91 ). Dextral torsion is a key feature of the Subfamily Cribroperidinioideae (Fensome et al.1993, Riding & Fensome 2002). Frigatadinium is more elongate and angular in outline than most species of Cribroperidinium whjch is typically ovoidal (Helenes 1984 ). Frigatadinium also normally has a short apical horn that may be composed of ornamentational features. Representatives of Cribroperidinium normally have a prominent apical horn that is consistently formed by autophragm. Frigatadinium also lacks the prominent intratabular ridges/ ornamentation al lineations that are common in Cribroperidinium. However the most characteristic feature of Frigatadinium is the marked suppres ion of the parasutures in the ventral area (Fig. 2). Note that the elongate 1 p paraplate is not defined and the parasutures defining the 1' and 2 paraplates are much reduced. Some species of Cribroperidinium do not exhibit any parasutures within the parasulcus for example Cribroperidinium diaphane (Cookson & Eisenack 195 8 Sto er & Evitt 1978. These forms, bowe er all have clear ''' 2 and 1 p paraplates (Helenes, 1984 pl. 2, fig. 2). A similar phenomenon is present in certain other unrelated genera such as Gonyaulacysta Deflandre 1964 (see Jan du Chene eta!. 1986, pl. 37 figs 9, 14) and Impagidinium Stover & Evitt 1978 (see Jan du Chene et al. 1986 pl. 53 figs 3. 11) however as in Cribroperidinium diaphane, the suppression is not normally as prof ot1nd as in Frigatadinium. Ventral paratabulation is also poorly defined in Cyclonephelium Deflandre & Cookson 1955 and Glaphyrocysta Stover & Evitt 1978. The ventral suppression of parasuture is nevertheless relatively unusual among gonyaulacacean dinoflagellate cysts and the type species Frigatadinium frigatense cannot be readily accommodated in Cribroperidinium, therefore a new genus is required. The relatively wide parasulcus also distinguishes this genus from Cribroperidinium.
Derivation of name. From the Frigate-I well.