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Capisocysta lyellii
Capisocysta lyellii Head, 1998b, p.807-808, fig.1, nos.2,4,6; fig.5, nos.1-6.
Holotype: Head, 1998b, fig.1, no.2; fig.5, nos.3-4.
Type stratum and locality: Ramsholt Member, about 6.4 m above the base of the Coralline Crag Formation, Rockhall Wood, Suffolk, eastern England (see Head, 1997).
Occurrence: Recorded only from eastern England (this study) where it occurs rarely in samples NQI and NQ4 of Head (1997) from the Ramsholt Member (ca. 3.8-3.6 Ma; late early Pliocene), Coralline Crag Formation.
Stratigraphic range: Upper lower Pliocene of eastern England.
Age: Early Pliocene.
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Original description: [Head, 1998b]:
Diagnosis:
Spherical cysts with granulate to irregularly microreticulate outer surface.
Tabulation expressed extensively on hypocyst, with individual loss of plates 2-6’’’, lp, ps, and a plate pair representing 1’’’’. Sulcal plates ls and rs and first postcingular plate usually remain attached to epicyst forming a hyposulcal tab. Posterior sulcal plate (ps) widens posteriorly from its contact with left and right sulcal plates. Plate 4’’’ has a dithigmate geniculate posterior margin and the antapical region has a plate pair whose left plate (*1’’’’l) is pentagonal and right plate (*1’’’’r) is stenoplanate.
Description:
Cysts are spherical and proximate, and have a thin (less than 0.5 μm) wall whose outer surface varies from irregularly microreticulate (as on the holotype) to granulate. Preformed lines of weakness are absent from the epicyst, weakly and incompletely developed on the sulcus, and fully developed elsewhere on the hypocyst, causing complete dissociation into constituent plates as follows: five postcingular (2-6’’’), one posterior sulcal (ps), one posterior intercalary (Ip), and a pair of antapical homologues (*1’’’’l and *1’’’’r). Together these plates form a hypotractal compound archeopyle, with no apparent preferential order of plate loss. The right and left sulcal plates (rs and ls) and first postcingular plate (1’’’) always remain attached to the epicyst as a hyposulcal tab. Plates of the hyposulcal tab are usually completely fused, but an angular notch on the posterior margin of the hyposulcal tab, always to the right of center, delimits the shared contact of left and right sulcal plates and corresponds to a projection on the contacting margin of the posterior sulcal plate (which fully detaches). The right and left sulcal plates are occasionally partly delimited by lines of weakness. The sulcus is quite strongly inclined to the right on the hypocyst. The posterior sulcal plate (ps), which anteriorly abuts the hyposulcal tab, widens away from the tab and posteriorly contacts 5’’’ (on the shortest side), *1’’’’l, and *1’’’’r. There are five postcingular plates of which 5’’’ is wider than 3’’’, resulting in 4’’’ being offset to the left. Plate 4’’’ is large and has a dithigmate geniculate posterior margin. Plates 3’’’ and 5’’’ are both camerate, having characteristic arcuate indentations at their posterioventral corners where they contact plates lp and ps respectively. Plate 5’’’ always has a smaller indentation than 3’’’. The posterior intercalary (lp) is relatively small and comparable in size to 6’’’. Two plates, here labelled left and right first antapical homologues (*1’’’’l and *1’’’’r), occur at the antapex. Plate *1’’’’l is pentagonal, its narrowest margin contacting ps. Plate *1’’’’r is stenoplanate whose convex narrower margins contact ps and 4’’’. The dorsal margins of these antapical plates contact the geniculate, dithigmate posterior margin of 4' ''. These two plates can be viewed as a single, broadly quinqueform (fivesided) first antapical plate surrounded by five other plates. Specimens otherwise closely resemble C. lata including the position of minute acute projections on the anterior margins of the postcingular series. No undehisced specimens were observed, and it was not possible to determine if specimens originally bore a loose, diaphanous outer layer as in C. lata.
Dimensions:
Holotype: maximum diameter of epicyst (excluding hypocystal tab) 55 μm.
Range: maximum diameter of epicyst (excluding hypocystal tab) in dehisced cysts, 49(54.5)66 μm. Six specimens were measured.
Affinities:
C. lata has a single antapical plate (I"") whereas C. lyellii has an antapical plate pair (*1’’’’l and *1’’’’r). Both of the antapicals in C. lyellii contact 4’’’, which is slightly offset to the left and has a posterior margin that is geniculate and dithigmate, in contrast to the mid-dorsal position and rectilinear monothigmate posterior margin of 4"' in C. lata. The ps in C. lyellii is somewhat larger than in C. lata and widens posteriorly. Ornament varies from smooth to granulate in C. lata and is nearly smooth to granulate or irregularly microreticulate in C. lye llii.
Discussion: C. lyellii is regarded as a species distinct from C. lata because 1) it differs in the presence of two antapical plates in place of one; 2) this difference has a subtle but pervasive effect on the geometry and topology of other hypocystal plates; and 3) C. lyellii was not seen in the Pliocene of the Clino borehole, Bahamas, despite the identification of numerous specimens of C. lata.
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Autecology:
This species lived in the warm-temperate, neritic waters of the southern North Sea during the late early Pliocene. The Ramsholt Member of the Coralline Crag Formation is a carbonate silty sand deposited at a water depth of at least 50 m (Hodgson and Funnell, 1987). It is not known whether the dinoflagellates lived in waters this deep or if the cysts were transported from shallower areas.
Holotype: Head, 1998b, fig.1, no.2; fig.5, nos.3-4.
Type stratum and locality: Ramsholt Member, about 6.4 m above the base of the Coralline Crag Formation, Rockhall Wood, Suffolk, eastern England (see Head, 1997).
Occurrence: Recorded only from eastern England (this study) where it occurs rarely in samples NQI and NQ4 of Head (1997) from the Ramsholt Member (ca. 3.8-3.6 Ma; late early Pliocene), Coralline Crag Formation.
Stratigraphic range: Upper lower Pliocene of eastern England.
Age: Early Pliocene.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Head, 1998b]:
Diagnosis:
Spherical cysts with granulate to irregularly microreticulate outer surface.
Tabulation expressed extensively on hypocyst, with individual loss of plates 2-6’’’, lp, ps, and a plate pair representing 1’’’’. Sulcal plates ls and rs and first postcingular plate usually remain attached to epicyst forming a hyposulcal tab. Posterior sulcal plate (ps) widens posteriorly from its contact with left and right sulcal plates. Plate 4’’’ has a dithigmate geniculate posterior margin and the antapical region has a plate pair whose left plate (*1’’’’l) is pentagonal and right plate (*1’’’’r) is stenoplanate.
Description:
Cysts are spherical and proximate, and have a thin (less than 0.5 μm) wall whose outer surface varies from irregularly microreticulate (as on the holotype) to granulate. Preformed lines of weakness are absent from the epicyst, weakly and incompletely developed on the sulcus, and fully developed elsewhere on the hypocyst, causing complete dissociation into constituent plates as follows: five postcingular (2-6’’’), one posterior sulcal (ps), one posterior intercalary (Ip), and a pair of antapical homologues (*1’’’’l and *1’’’’r). Together these plates form a hypotractal compound archeopyle, with no apparent preferential order of plate loss. The right and left sulcal plates (rs and ls) and first postcingular plate (1’’’) always remain attached to the epicyst as a hyposulcal tab. Plates of the hyposulcal tab are usually completely fused, but an angular notch on the posterior margin of the hyposulcal tab, always to the right of center, delimits the shared contact of left and right sulcal plates and corresponds to a projection on the contacting margin of the posterior sulcal plate (which fully detaches). The right and left sulcal plates are occasionally partly delimited by lines of weakness. The sulcus is quite strongly inclined to the right on the hypocyst. The posterior sulcal plate (ps), which anteriorly abuts the hyposulcal tab, widens away from the tab and posteriorly contacts 5’’’ (on the shortest side), *1’’’’l, and *1’’’’r. There are five postcingular plates of which 5’’’ is wider than 3’’’, resulting in 4’’’ being offset to the left. Plate 4’’’ is large and has a dithigmate geniculate posterior margin. Plates 3’’’ and 5’’’ are both camerate, having characteristic arcuate indentations at their posterioventral corners where they contact plates lp and ps respectively. Plate 5’’’ always has a smaller indentation than 3’’’. The posterior intercalary (lp) is relatively small and comparable in size to 6’’’. Two plates, here labelled left and right first antapical homologues (*1’’’’l and *1’’’’r), occur at the antapex. Plate *1’’’’l is pentagonal, its narrowest margin contacting ps. Plate *1’’’’r is stenoplanate whose convex narrower margins contact ps and 4’’’. The dorsal margins of these antapical plates contact the geniculate, dithigmate posterior margin of 4' ''. These two plates can be viewed as a single, broadly quinqueform (fivesided) first antapical plate surrounded by five other plates. Specimens otherwise closely resemble C. lata including the position of minute acute projections on the anterior margins of the postcingular series. No undehisced specimens were observed, and it was not possible to determine if specimens originally bore a loose, diaphanous outer layer as in C. lata.
Dimensions:
Holotype: maximum diameter of epicyst (excluding hypocystal tab) 55 μm.
Range: maximum diameter of epicyst (excluding hypocystal tab) in dehisced cysts, 49(54.5)66 μm. Six specimens were measured.
Affinities:
C. lata has a single antapical plate (I"") whereas C. lyellii has an antapical plate pair (*1’’’’l and *1’’’’r). Both of the antapicals in C. lyellii contact 4’’’, which is slightly offset to the left and has a posterior margin that is geniculate and dithigmate, in contrast to the mid-dorsal position and rectilinear monothigmate posterior margin of 4"' in C. lata. The ps in C. lyellii is somewhat larger than in C. lata and widens posteriorly. Ornament varies from smooth to granulate in C. lata and is nearly smooth to granulate or irregularly microreticulate in C. lye llii.
Discussion: C. lyellii is regarded as a species distinct from C. lata because 1) it differs in the presence of two antapical plates in place of one; 2) this difference has a subtle but pervasive effect on the geometry and topology of other hypocystal plates; and 3) C. lyellii was not seen in the Pliocene of the Clino borehole, Bahamas, despite the identification of numerous specimens of C. lata.
---------------------------------------
Autecology:
This species lived in the warm-temperate, neritic waters of the southern North Sea during the late early Pliocene. The Ramsholt Member of the Coralline Crag Formation is a carbonate silty sand deposited at a water depth of at least 50 m (Hodgson and Funnell, 1987). It is not known whether the dinoflagellates lived in waters this deep or if the cysts were transported from shallower areas.