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Limbodinium
From Williams et al., 2017:
[Limbodinium, Riding, 1987b, p. 56, 58, 60, 64
Type species: originally as Dinopterygium absidatum, Drugg, 1978 (pl.4, fig.7)] ; Limbodinium absidiatum, emend. Riding, 1987
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Original description: [Riding, 1987]:
Diagnosis:
Proximate, partially to fully suturocavate dinoflagellate cysts; hypocyst conical, epicyst nearly flat in equatorial view, subcircular in polar view; uncompressed to minimally dorsoventrally compressed. Paratabulation sexiform gonyaulacoid, indicated partially to completely by parasutural ornament that varies from low, smooth ridges to prominent crests which may be surmounted by low-relief ornamentation. Kofoidian paratabulation formula (Taylor/Evitt notation given in parentheses): Xpr 4` (lu, A-C), 6`` (li, 2-6), 6c (au-fi), 6``` (Iu-VI), lp (X), 1```` (Y), Xs.
Paracingulum bordered by a prominent, consistently cavate posterior flange and an anterior flange which may or may not be cavate. Five normally subtriangular claustra penetrate the anterior layer of the posterior paracingular flange at the positions of the paracingular parasutures. Archeopyle hemicystal (Bujak in Bujak et al., 1980, p.40).
Description:
Shape: Hypocyst a truncated cone. Epicyst a low cone, nearly flat. Both cyst portions subcircular in polar view.
Wall relationships: Endophragm and periphragm are normally closely appressed. However, these layers may separate at the parasutures, which are constructed of periphragm, giving rise to a suturocavate condition. The posterior paracingular flange is consistently cavate, whereas its anterior counterpart may be similarly cavate or acavate.
Wall features: Endophragm and periphragm smooth to ornamented with small, low-relief features. Periphragm forms continuous to discontinuous parasutural ridges or crests which may be smooth or surmounted by low-relief ornamentation (e.g. denticles). Normally the parasutural features are particularly well developed around the antapical paraplate.
Paratabulation: Sexiform gonyaulacoid, indicated partially to completely by parasutural ridges or crests. Kofoidian formula (Taylor/Evitt notation given in parentheses): Xpr, 4` (lu, A-C), 6" (li, 2-6), 6c (au-fi), 6"` (Iu-VI), lp (X), 1"" (Y), Xs. L-type ventral organization.
Archeopyle: Hemicystal, principal archeopyle suture straight, located within the paracingulum. Operculum attached ventrally, often folded into the
hypocyst.
Paracingulum: Laevorotatory, differing in lateral position by 1 to 1.5 paracingular widths; bordered by prominent flanges constructed of periphragm, which may be smooth or surmounted by low-relief ornamentation. The posterior flange is cavate, the layers being slightly separate. The anterior layer is penetrated by five subtriangular claustra situated at the positions of the paracingular parasutures, which are normally suppressed. The anterior flange may or may not be cavate.
Parasulcus: Longitudinal (L-type of Evitt, 1985), indicated by low parasulcal ridges, crests or a shallow concavity. Intraparasulcal parasutures normally suppressed.
Size: Intermediate to large (of Stover and Evitt, 1978, p.5).
Discussion:
The members of the Heteraulacacysta complex with hemicystal archeopyles (Dinopterygium, Heteraulacacysta and Tubidermodinium) are confined to the late Early Cretaceous to Neogene, with a diversity peak in the Paleogene (Evitt, 1985, p. 180). This small group previously included all genera with unequivocal hemicystal archeopyles. The recognition of this feature in Limbodinium means that it is no longer confined to the Heteraulacacysta complex. Limbodinium is also the oldest genus having the principal archeopyle suture located within the paracingulum and, perhaps more significantly, the only known sexiform genus with a hemicystal archeopyle.
However, Drugg (1978) implicitly interpreted the archeopyle type of Glossodinium dimorphum Ioannides et al. 1977 emend. Courtinat & Gaillard 1980 as being hemicystal. Drugg stated (p. 67) of G. dimorphum: "The epicystal archeopyle is formed by a separation through the paracingulum. As a result paracingular flanges are present on both epicyst and hypocyst." The species was transferred to Dinopterygium by Drugg (1978) on the basis of this and other observations. The interpretation of the hemicystal archeopyle is supported by a scanning electron photomicrograph of an isolated epicyst of "D." dimorphum with the anterior paracingular flange apparently adherent (Drugg, 1978, pl. 3, fig. 1). However, a similar photograph of an isolated hypocyst (Drugg, 1978, pl. 2, fig. 11) shows both paracingular flanges, presumably with the principal archeopyle suture immediately anterior to the paracingulum. There has been much debate as to the nature of the archeopyle in this distinctive Oxfordian to Portlandian species. The holotype (Ioannides et al., 1977, pl. 2, fig. 13) appears to exhibit a single paraplate precingular excystment aperture and was interpreted as such by the authors. Subsequent to the work of Drugg (1978), Courtinat and Gaillard ( 1980) rejected Drugg`s transfer to Dinopterygium and emended Glossodinium to give a paratabulation formula and reinterpret the archeopyle as combination type (tAa) + 3P. This confused situation strongly suggests that G. dimorphum exhibits archeopyle variability (see Stover and Evitt, 1978, Appendix E). It appears that it may exhibit a hemicystal archeopyle, but further work is needed to fully assess the nature of the excystment aperture in this form.
Affinities:
Limbodinium closely resembles in general morphology the three members of the Wanaea complex of Gs-Cysts of Evitt (1985, p. 222) Energlynia Sarjeant 1976, Isthmocystis Duxbury 1979, and Wanaea Cookson & Eisenack 1958. These three genera are characterized by a subconical hypocyst and a smaller, often nearly flat, epicyst which is rarely fully paratabulate. Limbodinium differs from Wanaea in being partially to fully paratabulate
and in lacking both the antapical horn and the complex, lacelike (acavate) posterior paracingular flange of that genus. Energlynia may be partially paratabulate, but lacks prominent paracingular flanges and, like Wanaea, has an antapical horn. Limbodinium most closely resembles Isthmocystis; both genera are paratabulate with wide, perforate posterior paracingular flanges. Isthmocystis, however, has an apical horn, lacks cavate paracingular flanges, and has a 6P archeopyle. Limbodinium, unlike the Wanaea complex, possesses a hemicystal, as opposed to an epicystal, archeopyle (the principal archeopyle suture in the latter type lying immediately anterior to the paracingulum). Limbodinium is similar to Dinopterygium (and other members of the Heteraulacacysta complex of Gq-quinqueform-cysts of Evitt, 1985) in that both open by means of a hemicystal archeopyle. However, Dinopterygium is quinqueform, has a hemispherical epicyst which equals (or closely approaches) the hypocyst in length, and is holocavate. It also exhibits groups of tubercles or cylindrical structures between the autophragm and ectophragm. Heteraulacacysta Drugg & Loeblich 1967 resembles Limbodinium in archeopyle type, but has thin peri- and endophragm and is clearly quinqueform. The monotypic genus Tubidermodinium Morgenroth 1966 also appears to have a hemicystal archeopyle. This form differs from Limbodinium in being quinqueform and holocavate, the ectophragm being extended into intratabular clusters of funnel-shaped structures which abut against the autophragm. In addition, Dinopterygium, Heteraulacacysta, and Tubidermodinium (all members of the Heteraulacacysta complex) lack the distinctive anteriorly perforate, consistently cavate posterior paracingular flange of Limbodinium.
[Limbodinium, Riding, 1987b, p. 56, 58, 60, 64
Type species: originally as Dinopterygium absidatum, Drugg, 1978 (pl.4, fig.7)] ; Limbodinium absidiatum, emend. Riding, 1987
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Riding, 1987]:
Diagnosis:
Proximate, partially to fully suturocavate dinoflagellate cysts; hypocyst conical, epicyst nearly flat in equatorial view, subcircular in polar view; uncompressed to minimally dorsoventrally compressed. Paratabulation sexiform gonyaulacoid, indicated partially to completely by parasutural ornament that varies from low, smooth ridges to prominent crests which may be surmounted by low-relief ornamentation. Kofoidian paratabulation formula (Taylor/Evitt notation given in parentheses): Xpr 4` (lu, A-C), 6`` (li, 2-6), 6c (au-fi), 6``` (Iu-VI), lp (X), 1```` (Y), Xs.
Paracingulum bordered by a prominent, consistently cavate posterior flange and an anterior flange which may or may not be cavate. Five normally subtriangular claustra penetrate the anterior layer of the posterior paracingular flange at the positions of the paracingular parasutures. Archeopyle hemicystal (Bujak in Bujak et al., 1980, p.40).
Description:
Shape: Hypocyst a truncated cone. Epicyst a low cone, nearly flat. Both cyst portions subcircular in polar view.
Wall relationships: Endophragm and periphragm are normally closely appressed. However, these layers may separate at the parasutures, which are constructed of periphragm, giving rise to a suturocavate condition. The posterior paracingular flange is consistently cavate, whereas its anterior counterpart may be similarly cavate or acavate.
Wall features: Endophragm and periphragm smooth to ornamented with small, low-relief features. Periphragm forms continuous to discontinuous parasutural ridges or crests which may be smooth or surmounted by low-relief ornamentation (e.g. denticles). Normally the parasutural features are particularly well developed around the antapical paraplate.
Paratabulation: Sexiform gonyaulacoid, indicated partially to completely by parasutural ridges or crests. Kofoidian formula (Taylor/Evitt notation given in parentheses): Xpr, 4` (lu, A-C), 6" (li, 2-6), 6c (au-fi), 6"` (Iu-VI), lp (X), 1"" (Y), Xs. L-type ventral organization.
Archeopyle: Hemicystal, principal archeopyle suture straight, located within the paracingulum. Operculum attached ventrally, often folded into the
hypocyst.
Paracingulum: Laevorotatory, differing in lateral position by 1 to 1.5 paracingular widths; bordered by prominent flanges constructed of periphragm, which may be smooth or surmounted by low-relief ornamentation. The posterior flange is cavate, the layers being slightly separate. The anterior layer is penetrated by five subtriangular claustra situated at the positions of the paracingular parasutures, which are normally suppressed. The anterior flange may or may not be cavate.
Parasulcus: Longitudinal (L-type of Evitt, 1985), indicated by low parasulcal ridges, crests or a shallow concavity. Intraparasulcal parasutures normally suppressed.
Size: Intermediate to large (of Stover and Evitt, 1978, p.5).
Discussion:
The members of the Heteraulacacysta complex with hemicystal archeopyles (Dinopterygium, Heteraulacacysta and Tubidermodinium) are confined to the late Early Cretaceous to Neogene, with a diversity peak in the Paleogene (Evitt, 1985, p. 180). This small group previously included all genera with unequivocal hemicystal archeopyles. The recognition of this feature in Limbodinium means that it is no longer confined to the Heteraulacacysta complex. Limbodinium is also the oldest genus having the principal archeopyle suture located within the paracingulum and, perhaps more significantly, the only known sexiform genus with a hemicystal archeopyle.
However, Drugg (1978) implicitly interpreted the archeopyle type of Glossodinium dimorphum Ioannides et al. 1977 emend. Courtinat & Gaillard 1980 as being hemicystal. Drugg stated (p. 67) of G. dimorphum: "The epicystal archeopyle is formed by a separation through the paracingulum. As a result paracingular flanges are present on both epicyst and hypocyst." The species was transferred to Dinopterygium by Drugg (1978) on the basis of this and other observations. The interpretation of the hemicystal archeopyle is supported by a scanning electron photomicrograph of an isolated epicyst of "D." dimorphum with the anterior paracingular flange apparently adherent (Drugg, 1978, pl. 3, fig. 1). However, a similar photograph of an isolated hypocyst (Drugg, 1978, pl. 2, fig. 11) shows both paracingular flanges, presumably with the principal archeopyle suture immediately anterior to the paracingulum. There has been much debate as to the nature of the archeopyle in this distinctive Oxfordian to Portlandian species. The holotype (Ioannides et al., 1977, pl. 2, fig. 13) appears to exhibit a single paraplate precingular excystment aperture and was interpreted as such by the authors. Subsequent to the work of Drugg (1978), Courtinat and Gaillard ( 1980) rejected Drugg`s transfer to Dinopterygium and emended Glossodinium to give a paratabulation formula and reinterpret the archeopyle as combination type (tAa) + 3P. This confused situation strongly suggests that G. dimorphum exhibits archeopyle variability (see Stover and Evitt, 1978, Appendix E). It appears that it may exhibit a hemicystal archeopyle, but further work is needed to fully assess the nature of the excystment aperture in this form.
Affinities:
Limbodinium closely resembles in general morphology the three members of the Wanaea complex of Gs-Cysts of Evitt (1985, p. 222) Energlynia Sarjeant 1976, Isthmocystis Duxbury 1979, and Wanaea Cookson & Eisenack 1958. These three genera are characterized by a subconical hypocyst and a smaller, often nearly flat, epicyst which is rarely fully paratabulate. Limbodinium differs from Wanaea in being partially to fully paratabulate
and in lacking both the antapical horn and the complex, lacelike (acavate) posterior paracingular flange of that genus. Energlynia may be partially paratabulate, but lacks prominent paracingular flanges and, like Wanaea, has an antapical horn. Limbodinium most closely resembles Isthmocystis; both genera are paratabulate with wide, perforate posterior paracingular flanges. Isthmocystis, however, has an apical horn, lacks cavate paracingular flanges, and has a 6P archeopyle. Limbodinium, unlike the Wanaea complex, possesses a hemicystal, as opposed to an epicystal, archeopyle (the principal archeopyle suture in the latter type lying immediately anterior to the paracingulum). Limbodinium is similar to Dinopterygium (and other members of the Heteraulacacysta complex of Gq-quinqueform-cysts of Evitt, 1985) in that both open by means of a hemicystal archeopyle. However, Dinopterygium is quinqueform, has a hemispherical epicyst which equals (or closely approaches) the hypocyst in length, and is holocavate. It also exhibits groups of tubercles or cylindrical structures between the autophragm and ectophragm. Heteraulacacysta Drugg & Loeblich 1967 resembles Limbodinium in archeopyle type, but has thin peri- and endophragm and is clearly quinqueform. The monotypic genus Tubidermodinium Morgenroth 1966 also appears to have a hemicystal archeopyle. This form differs from Limbodinium in being quinqueform and holocavate, the ectophragm being extended into intratabular clusters of funnel-shaped structures which abut against the autophragm. In addition, Dinopterygium, Heteraulacacysta, and Tubidermodinium (all members of the Heteraulacacysta complex) lack the distinctive anteriorly perforate, consistently cavate posterior paracingular flange of Limbodinium.