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Phthanoperidinium amiculum
Phthanoperidinium amiculum Liengjarern et al., 1980
Holotype: Liengjarern et al., 1980, pl.53, fig.4
Locus typicus: Whitecliff Bay, Isle of Wight, England
Stratum typicum: Late Eocene
Original diagnosis: Liengjarern et al., 1980, p.487-488
Phthanoperidinium with ambitus rounded-pentagonal to suboval. Epicyst with convex sides, terminating in a short apical horn, hypocyst also rounded, produced into one, very occasionally two, antapical horns. Peri- and endophragm very closely appressed except beneath the horns, where restricted pericoels develop. Periphragm ornamented with intratabular spinules and penitabular to hyaline sutural ridges with smooth to slightly denticulate free edges. Laevigate to striate pandasutural lines may be distinct. Pericingulum and perisulcus laevigate, bordered by membranes.
Original discription: Liengjarern et al., 1980, p.488
The pericyst is fusiform in lateral view; the ambitus is rounded-peridinoid to subcircular or suboval. The apical horn is short, trangular and distally blunt. The left antapical horn is usually well developed. On some specimens, a right antapical horn, very much reduced, may occur; on most specimens, a projection of the sutural ridges takes the place of the right antapical horn. The intratabular spines are small and solid, distally short or somewhat capitate; those closer to the paraplate periphery may be arranged in a penitabular ring. The ridges are hyaline and imperforate, their free margins are entire or very slightly serrate to denticulate; the height of the ridges normally does not exceed 3 µm, except along the cingular sutures where they may be up to 5 µm in height. The ridges may be parasutural or penitabular in position. Narrow laevigate pandasutural zones are normally observable on parts of the pericyst and, on some specimens, very faint striations, perpendicular to the margin of the paraplate, may be observable. The paratabulation formula and shape of the paraplates are normal for the genus. The pericingulum is helicoid, its ends being offset about one pericingular width; its surface is laevigate. The perisulcus is relatively narrow, moderately excavated, extending anteriorly to nearly a half of the epicyst height. The archeopyle is
formed by the detachment of paraplate 2a, but it is only rarely observable. Occasionally, additional sutures occur along the margins of all three intercalary plates. Dimenisons. Holotype, pericyst length 63 µm, breadth 48 µm, apical horn 7 µm, left antapical horn 5.5 µm. Range. Pericyst length 47(55.5)63 µm, breadth 40(43)48 µm, apical horn 3(5.5)7 µm, left antapical horn 3(5.5)7 µm. Specimens measured 10.
Affinities:
Liengjarern et al., 1980, p.488: P. eocenicum (Cookson and Eisenack 1965) appears to have sutural ridges and intratabular granules, and thus resembles P. amiculum in the style of ornament; but the ambitus in P. eocenicum is fusiform to subpolygonal, less rounded than P. amiculum and the left antapical horn lies closer lo the median axis: in addition both intratabular granules and sutural ridges are much more reduced than on the present species.
P. alectrolophum Eaton 1976 resembles P. amiculum in possessing sutural-penitabular ridges, but these bear well-developed spines on their free margins and the intratabular paraplate surfaces are smooth.
Holotype: Liengjarern et al., 1980, pl.53, fig.4
Locus typicus: Whitecliff Bay, Isle of Wight, England
Stratum typicum: Late Eocene
Original diagnosis: Liengjarern et al., 1980, p.487-488
Phthanoperidinium with ambitus rounded-pentagonal to suboval. Epicyst with convex sides, terminating in a short apical horn, hypocyst also rounded, produced into one, very occasionally two, antapical horns. Peri- and endophragm very closely appressed except beneath the horns, where restricted pericoels develop. Periphragm ornamented with intratabular spinules and penitabular to hyaline sutural ridges with smooth to slightly denticulate free edges. Laevigate to striate pandasutural lines may be distinct. Pericingulum and perisulcus laevigate, bordered by membranes.
Original discription: Liengjarern et al., 1980, p.488
The pericyst is fusiform in lateral view; the ambitus is rounded-peridinoid to subcircular or suboval. The apical horn is short, trangular and distally blunt. The left antapical horn is usually well developed. On some specimens, a right antapical horn, very much reduced, may occur; on most specimens, a projection of the sutural ridges takes the place of the right antapical horn. The intratabular spines are small and solid, distally short or somewhat capitate; those closer to the paraplate periphery may be arranged in a penitabular ring. The ridges are hyaline and imperforate, their free margins are entire or very slightly serrate to denticulate; the height of the ridges normally does not exceed 3 µm, except along the cingular sutures where they may be up to 5 µm in height. The ridges may be parasutural or penitabular in position. Narrow laevigate pandasutural zones are normally observable on parts of the pericyst and, on some specimens, very faint striations, perpendicular to the margin of the paraplate, may be observable. The paratabulation formula and shape of the paraplates are normal for the genus. The pericingulum is helicoid, its ends being offset about one pericingular width; its surface is laevigate. The perisulcus is relatively narrow, moderately excavated, extending anteriorly to nearly a half of the epicyst height. The archeopyle is
formed by the detachment of paraplate 2a, but it is only rarely observable. Occasionally, additional sutures occur along the margins of all three intercalary plates. Dimenisons. Holotype, pericyst length 63 µm, breadth 48 µm, apical horn 7 µm, left antapical horn 5.5 µm. Range. Pericyst length 47(55.5)63 µm, breadth 40(43)48 µm, apical horn 3(5.5)7 µm, left antapical horn 3(5.5)7 µm. Specimens measured 10.
Affinities:
Liengjarern et al., 1980, p.488: P. eocenicum (Cookson and Eisenack 1965) appears to have sutural ridges and intratabular granules, and thus resembles P. amiculum in the style of ornament; but the ambitus in P. eocenicum is fusiform to subpolygonal, less rounded than P. amiculum and the left antapical horn lies closer lo the median axis: in addition both intratabular granules and sutural ridges are much more reduced than on the present species.
P. alectrolophum Eaton 1976 resembles P. amiculum in possessing sutural-penitabular ridges, but these bear well-developed spines on their free margins and the intratabular paraplate surfaces are smooth.