Back
Hystrichostrogylon sulcatum
Hystrichostrogylon sulcatum Guerstein et al., 2004, p.332,336, figs.4a–f,5a–l,6a–c.
Holotype: Guerstein et al., 2004, figs.4a–b,5a–c.
Age: late Oligocene to early Miocene.
Original description (Guerstein et al., 2004):
Hystrichostrogylon sulcatum sp. nov. Fig. 4a-f, Fig. 5a-l, Fig. 6a-c
Holotype: Laboratory of Palynology Universidad Nacional del Sur (UNSLP) slide no. LA-26 45 • 102. England Finder L31/3, Fig. 4 a & b, Fig. 5 a-c.
Type locality." Centinela Formation, Bandurrias River, southern Calafate, Santa Cruz, Argentina.
Stratigraphic horizon: Centinela Formation, at 140 m above the base of the section (Fig. 2).
Stratigraphic occurrence." Upper Oligocene to Lower Miocene.
Etymology." Adjective derived from the Latin sulcus: ventral furrow or groove in reference to the mid-ventral position of the cavation.
Diagnosis: A species of Hystrichostrogylon characterized by a narrow mid-ventral cavation and an antapical structure composed of two large gonal processes joined by a suturocavate membrane. All the processes are hollow, tapering, trifurcate with solid distal ends.
Description." Cysts camocavate with spherical to subspherical central body. Endophragm smooth, periphragm finely granulate, always appressed except on the sulcal area, where endophragm and periphragm are narrowly separated. The pericoel communicates with the exterior through a small hole or claustrum in the mid-ventral part of the periphragm. The processes are variable in size and shape. Most of the processes are gonal, triangular in cross-section, broad, tapering, hollow, joined proximally by very faint sutural ridges. Distally the processes are trifurcate with solid ends. The apex of the cyst is consistently indicated by a single, thin, distally bifid process. Processes on opposite margins of the cingulum may be connected in pairs by relatively high membranes. Two large antapical processes are joined at their bases by a common suturocavate membrane developing an antapical structure. The height of the processes varies depending on the degree of cavation, resulting in shorter processes at the sulcus than elsewhere. Archeopyle precingular, formed by the loss of plate 3".
Dimensions: Central body length: 32 (49) 65 µm (40 specimens measured); central body width: 32 (45) 55 µm (20 specimens measured); processes length: 8-18 µm; antapical process structure: length 13 (15) 17 µm; width 19 (24) 34 µm (16 specimens measured).
Comparisons." This species of Hystriehostrogylon is characterized by a pericoel confined to the sulcal area with a small claustrum at the midventral part of the periphragm. In both Hystrichostrogylon borisii Schioler 1993 and H. coninckii Heilmann-Clausen in Thompsen and Heilmann-Clausen (1985) the endophragm and periphragm are appressed dorsally, but with relatively large ventral pericoels, and a large rounded mid-ventral claustrum, in the periphragm. In H. membraniphorum Agelopoulos 1964 the pericoel is only developed antapically, although according to Eaton (1976), this species (as Achomosphaera membraniphora) forms a distinctive pericoel in the antapical and ventral areas. In H. holohymenium Islam 1983 the pericoel almost completely surrounds the endocyst, whereas in H. clausenii Bujak 1994 the periphragm and endophragm are in contact in the mid-dorsal and mid-ventral regions with a pericoel surounding the ambital periphery of the cyst; the claustrum is typically developed on the left cingular-postcingular side of the periphragm. The new species described here differs from all other species of Hystrichostrogylon in having a characteristic antapical process structure. The features of H. sulcatum strongly resemble those described for Spiniferitesfalcipedius Warny & Wrenn 1997. These two species also have in common a consistent, thin preapical process and with the cingular area defined by pairs of processes transversally joined by high membranes. In dorso-ventral view H. sulcatum is therefore remarkably similar to Spiniferites falcipedius (Fig. 6e & f). However, most of the specimens recovered from the Centinela Formation show the sulcal pericoel, a feature obviously absent in S. falcipedius. The morphological features shared by these two species suggest a close relationship.
Remarks. The antapical process structure and the distal process morphology show a gradational variation within the dinoflagellate cyst assemblages recovered from the Centinela Formation. Warny & Wrenn (1997) have already noted a gradation between specimens sharing characteristics of Spiniferites mirabilis (Rossignol) Sarjeant 1979 and S. falcipedius, from the upper Neogene succession of the Atlantic Coast of Morocco. These authors suggested an evolutionary relationship between the two species. Similarly, some Argentinian specimens of H. sulcatum and Spiniferites falcipedius (Fig. 6e-f) possess broad, gonal and distally solid processes with an antapical process structure giving rise to three short bifurcate and trifurcate processes, typical of S. mirabilis (Fig. 6e & f). Other specimens bear thin, trifurcate gonal and bifurcate intergonal processes with an antapical structure as in S. mirabilis, but possess the sulcal cavation (Fig. 6d). The last case was only observed in the assemblages from the lower part of the section.
Holotype: Guerstein et al., 2004, figs.4a–b,5a–c.
Age: late Oligocene to early Miocene.
Original description (Guerstein et al., 2004):
Hystrichostrogylon sulcatum sp. nov. Fig. 4a-f, Fig. 5a-l, Fig. 6a-c
Holotype: Laboratory of Palynology Universidad Nacional del Sur (UNSLP) slide no. LA-26 45 • 102. England Finder L31/3, Fig. 4 a & b, Fig. 5 a-c.
Type locality." Centinela Formation, Bandurrias River, southern Calafate, Santa Cruz, Argentina.
Stratigraphic horizon: Centinela Formation, at 140 m above the base of the section (Fig. 2).
Stratigraphic occurrence." Upper Oligocene to Lower Miocene.
Etymology." Adjective derived from the Latin sulcus: ventral furrow or groove in reference to the mid-ventral position of the cavation.
Diagnosis: A species of Hystrichostrogylon characterized by a narrow mid-ventral cavation and an antapical structure composed of two large gonal processes joined by a suturocavate membrane. All the processes are hollow, tapering, trifurcate with solid distal ends.
Description." Cysts camocavate with spherical to subspherical central body. Endophragm smooth, periphragm finely granulate, always appressed except on the sulcal area, where endophragm and periphragm are narrowly separated. The pericoel communicates with the exterior through a small hole or claustrum in the mid-ventral part of the periphragm. The processes are variable in size and shape. Most of the processes are gonal, triangular in cross-section, broad, tapering, hollow, joined proximally by very faint sutural ridges. Distally the processes are trifurcate with solid ends. The apex of the cyst is consistently indicated by a single, thin, distally bifid process. Processes on opposite margins of the cingulum may be connected in pairs by relatively high membranes. Two large antapical processes are joined at their bases by a common suturocavate membrane developing an antapical structure. The height of the processes varies depending on the degree of cavation, resulting in shorter processes at the sulcus than elsewhere. Archeopyle precingular, formed by the loss of plate 3".
Dimensions: Central body length: 32 (49) 65 µm (40 specimens measured); central body width: 32 (45) 55 µm (20 specimens measured); processes length: 8-18 µm; antapical process structure: length 13 (15) 17 µm; width 19 (24) 34 µm (16 specimens measured).
Comparisons." This species of Hystriehostrogylon is characterized by a pericoel confined to the sulcal area with a small claustrum at the midventral part of the periphragm. In both Hystrichostrogylon borisii Schioler 1993 and H. coninckii Heilmann-Clausen in Thompsen and Heilmann-Clausen (1985) the endophragm and periphragm are appressed dorsally, but with relatively large ventral pericoels, and a large rounded mid-ventral claustrum, in the periphragm. In H. membraniphorum Agelopoulos 1964 the pericoel is only developed antapically, although according to Eaton (1976), this species (as Achomosphaera membraniphora) forms a distinctive pericoel in the antapical and ventral areas. In H. holohymenium Islam 1983 the pericoel almost completely surrounds the endocyst, whereas in H. clausenii Bujak 1994 the periphragm and endophragm are in contact in the mid-dorsal and mid-ventral regions with a pericoel surounding the ambital periphery of the cyst; the claustrum is typically developed on the left cingular-postcingular side of the periphragm. The new species described here differs from all other species of Hystrichostrogylon in having a characteristic antapical process structure. The features of H. sulcatum strongly resemble those described for Spiniferitesfalcipedius Warny & Wrenn 1997. These two species also have in common a consistent, thin preapical process and with the cingular area defined by pairs of processes transversally joined by high membranes. In dorso-ventral view H. sulcatum is therefore remarkably similar to Spiniferites falcipedius (Fig. 6e & f). However, most of the specimens recovered from the Centinela Formation show the sulcal pericoel, a feature obviously absent in S. falcipedius. The morphological features shared by these two species suggest a close relationship.
Remarks. The antapical process structure and the distal process morphology show a gradational variation within the dinoflagellate cyst assemblages recovered from the Centinela Formation. Warny & Wrenn (1997) have already noted a gradation between specimens sharing characteristics of Spiniferites mirabilis (Rossignol) Sarjeant 1979 and S. falcipedius, from the upper Neogene succession of the Atlantic Coast of Morocco. These authors suggested an evolutionary relationship between the two species. Similarly, some Argentinian specimens of H. sulcatum and Spiniferites falcipedius (Fig. 6e-f) possess broad, gonal and distally solid processes with an antapical process structure giving rise to three short bifurcate and trifurcate processes, typical of S. mirabilis (Fig. 6e & f). Other specimens bear thin, trifurcate gonal and bifurcate intergonal processes with an antapical structure as in S. mirabilis, but possess the sulcal cavation (Fig. 6d). The last case was only observed in the assemblages from the lower part of the section.