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Lophocysta sulcolimbata
Lophocysta sulcolimbata Manum, 1979
Holotype: Manum, 1979, pl.1, figs.4-6, text-figs.1A-B
Age: Early Miocene
Original description: Manum, 1979, p.238
Dinoflagellate cysts with pentagonal, precingular archeopyle. Central body ovoid, with a prominent ventral crest formed by an expanded periphragm along the entire midventral zone, extending from anterior end of archeopyle to posterior end of parasulcus; maximum crest height about 2/3 equatorial diameter of central body. The crest has a finely reticulate to striate texture and more prominent parasutural ribs. The entire parasulcus plus paraplates 1" and 4", 6", 6c, 1""" and 6""", and 1p are represented in the crest. Three conspicuous openings are in constant positions at the base of the periphragm crest: one in either side at the intersections between crest and paracingulum, the third--and largest--opening immediately below the paracingular opening in the left hand side. Two further openings--inconspicuous and sometimes fused--occur in a position interpreted as the left accessory sulcal paraplate.
Inconspicuous processes, 1--3 Ám high, occur in some--but not all--gonal positions of dorsal paraplates. Most consistent are two in posterior end of paraplate 4" and eight occupying gonal positions of cingular paraplates.
Dorsal cyst wall apparently unstratified and slightly under 2 µm thick, surface entirely smooth.
Dimensions: Central body of holotype 46 X 40µm, of paratypes 46 X 36 µm and 51 X 39 µm.
Affinities: Manum, 1979, p. 240-243
The most distinctive feature of this species is its ventral crest running halfway round the cyst from the top of the archeopyle to the antapex, giving it an over-all appearance of a Roman helmet turned upside down. The cysts will almost invariably rest on the side in strew mounts because of the projecting crest. This, together with the scanty features to indicate orientation and paratabulation, led to misinterpretation of the few specimens observed during the first survey of the material. They were provisionally referred to Cyclor~ephelium since they mimic certain features in that genus. The true morphology of the species was realized when subsequently enough specimens were found to allow picking and manipulation. A double wall structure is evident in the region of the crest: a fibrous periphragm forms the crest, while the apparently structureless central body represents the endophragm. Outside the region occupied by the crest, there is no double wall structure to be seen.
The shape of the archeopyle and the arrangement of ornamental features (dorsal processes, ribs on the crest) are consistent with a gonyaulacacean paratabulation, as shown in the interpretation presented in Fig.1. Some of the paraplate boundaries and identifications are still tentative, particularly in the ventral zone of the hypocyst, where rib structures are quite crowded and difficult to resolve. The ribs in the epicyst, on the other hand, are more easy to interpret (cf. Fig.1E). On the whole, the rib structures are difficult to observe without the aid of interference phase contrast miscroscopy. Crest attachment to the central body appears in general to cut across paraplates, only in a few places does it seem to follow parasutures.
The two small openings observed in sulcal positions are strongly suggestive of reflecting flagellar pores. Like other thecal features reflected in the cyst (e.g., the cingulum) they are not considered to have been functional in the cyst stage, but merely genetically determined replications of motile stage structures.
The exclusively ventral pericoel places Lophocysta in a position of its own among known cysts. The over-all construction, however, has certain elements in common with Thalassiphora, and particularly with T. delicata Williams et Downie as illustrated and interpreted by Eaton (1976, p.285). In that species, too, a dorsal area is devoid of periphragm expansion, but the area is very much smaller than in L. sulcolimbata. Furthermore, paratabulation is reflected by ribs in the periphragm in a similar way, On the other hand, paratabulation in T. delicata as interpreted by Eaton (l.c.) differs significantly from L. sulcolimbata and from gonyaulacacean tabulations. In Fig.2 an alternative interpretation is presented for T. delicata which brings it more in line with known tabulations and also closer to L. sulcolimbata, however still not close enough to assume close relationship between them. The interpretation of T. delicata presented here also leaves areas of doubt, particularly with regard to the hypocyst, where relationships between paraplate 6"" (1p in Eaton"s interpretation) and adjacent paraplates become quite unusual; also, the 1p area (1"" in Eaton) would seem to require further exploration.
Holotype: Manum, 1979, pl.1, figs.4-6, text-figs.1A-B
Age: Early Miocene
Original description: Manum, 1979, p.238
Dinoflagellate cysts with pentagonal, precingular archeopyle. Central body ovoid, with a prominent ventral crest formed by an expanded periphragm along the entire midventral zone, extending from anterior end of archeopyle to posterior end of parasulcus; maximum crest height about 2/3 equatorial diameter of central body. The crest has a finely reticulate to striate texture and more prominent parasutural ribs. The entire parasulcus plus paraplates 1" and 4", 6", 6c, 1""" and 6""", and 1p are represented in the crest. Three conspicuous openings are in constant positions at the base of the periphragm crest: one in either side at the intersections between crest and paracingulum, the third--and largest--opening immediately below the paracingular opening in the left hand side. Two further openings--inconspicuous and sometimes fused--occur in a position interpreted as the left accessory sulcal paraplate.
Inconspicuous processes, 1--3 Ám high, occur in some--but not all--gonal positions of dorsal paraplates. Most consistent are two in posterior end of paraplate 4" and eight occupying gonal positions of cingular paraplates.
Dorsal cyst wall apparently unstratified and slightly under 2 µm thick, surface entirely smooth.
Dimensions: Central body of holotype 46 X 40µm, of paratypes 46 X 36 µm and 51 X 39 µm.
Affinities: Manum, 1979, p. 240-243
The most distinctive feature of this species is its ventral crest running halfway round the cyst from the top of the archeopyle to the antapex, giving it an over-all appearance of a Roman helmet turned upside down. The cysts will almost invariably rest on the side in strew mounts because of the projecting crest. This, together with the scanty features to indicate orientation and paratabulation, led to misinterpretation of the few specimens observed during the first survey of the material. They were provisionally referred to Cyclor~ephelium since they mimic certain features in that genus. The true morphology of the species was realized when subsequently enough specimens were found to allow picking and manipulation. A double wall structure is evident in the region of the crest: a fibrous periphragm forms the crest, while the apparently structureless central body represents the endophragm. Outside the region occupied by the crest, there is no double wall structure to be seen.
The shape of the archeopyle and the arrangement of ornamental features (dorsal processes, ribs on the crest) are consistent with a gonyaulacacean paratabulation, as shown in the interpretation presented in Fig.1. Some of the paraplate boundaries and identifications are still tentative, particularly in the ventral zone of the hypocyst, where rib structures are quite crowded and difficult to resolve. The ribs in the epicyst, on the other hand, are more easy to interpret (cf. Fig.1E). On the whole, the rib structures are difficult to observe without the aid of interference phase contrast miscroscopy. Crest attachment to the central body appears in general to cut across paraplates, only in a few places does it seem to follow parasutures.
The two small openings observed in sulcal positions are strongly suggestive of reflecting flagellar pores. Like other thecal features reflected in the cyst (e.g., the cingulum) they are not considered to have been functional in the cyst stage, but merely genetically determined replications of motile stage structures.
The exclusively ventral pericoel places Lophocysta in a position of its own among known cysts. The over-all construction, however, has certain elements in common with Thalassiphora, and particularly with T. delicata Williams et Downie as illustrated and interpreted by Eaton (1976, p.285). In that species, too, a dorsal area is devoid of periphragm expansion, but the area is very much smaller than in L. sulcolimbata. Furthermore, paratabulation is reflected by ribs in the periphragm in a similar way, On the other hand, paratabulation in T. delicata as interpreted by Eaton (l.c.) differs significantly from L. sulcolimbata and from gonyaulacacean tabulations. In Fig.2 an alternative interpretation is presented for T. delicata which brings it more in line with known tabulations and also closer to L. sulcolimbata, however still not close enough to assume close relationship between them. The interpretation of T. delicata presented here also leaves areas of doubt, particularly with regard to the hypocyst, where relationships between paraplate 6"" (1p in Eaton"s interpretation) and adjacent paraplates become quite unusual; also, the 1p area (1"" in Eaton) would seem to require further exploration.