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Hystrichokolpoma pacificum
Hystrichokolpoma pacificum Matsuoka, 1979, p.51,53-54, pl.1, figs.1-5; text-figs.3,5A. Holotype: Matsuoka, 1979, pl.1, figs.1-3; Fauconnier and Masure, 2004, pl.39, fig.5. Age: Early Pleistocene.
Original description, Matsuoka, 1979.
Diagnosis: Cyst ellipsoidal with finely granulose surface. Processes composed of two types: large hollow, subconical to short cylindrical with rectangular or pentagonal base and entirely to slightly denticulate distal ends; in the paracingular region, small hollow processes with rectangular base expanded transversely.
Holotype: Slide no. OKD-3, position 4pIII, Plate I, 1--3. Kisembaru, KimSon, Kunigami-Gun, Okinawa Prefecture, Japan.
Paratype: Slide no. OKD-4, position 7GIII, Plate I, 4--5, Kisembaru, KimSon, Kunigami-Gun Okinawa Prefecture, Japan.
Description: The cyst is ellipsoidal in equatorial view and circular in polar view. Its wall is composed of two layers, the peri- and endophragms, and both are appressed between processes. The outer surface of the periphragm bears minute granules and indistinct striations. Processes formed from the periphragm reflect the paratabulation of 4'(?), 0a, 6", 6c, 5'", lp, 1as, lps, and 3s(?). The archeopyle is formed by loss of all apical series. Precingular, postcingular and antapical paraplates are represented by large hollow, subconical to short cylindrical processes with entirely to slightly denticulate distal extremities, which do not communicate with the endocoel. Processes 3" and 4" have five-sided bases, while others possess four-sided bases. Processes 3" and 6" are larger than other precingular processes, with the 1" process being the smallest. Each cingular paraplate has one small hollow process with a rectangular transversely expanded base and entirely to slightly
denticulate distal ends. The parasulcal region shows at least three small processes and two intermediate ones which may reflect original anterior and posterior sulcal plates. The paracingulum may be slightly displaced. The anterior sulcal process, intermediate in size and hollow with entirely or slightly denticulate distal ends, is situated between processes 1" and 6". An intermediate and hollow process with quadrate base is located between postcingular process 5'" and the posterior intercalary process. Owing to its size and position, this process probably represents the posterior sulcal, and not the sixth postcingular paraplate. Except for anterior and posterior sulcal process, three small processes with quadrate base and entirely to slightly denticulate distal extremities are observed in the parasulcal region. The postcingular process 1"' is the smallest among its series and all processes assigned to the postcingulum have quadrate bases. The antapical process with
pentagonal base is the largest, cylindrical in dorso-ventral view with the large triangular distal appendix observed on the dorsal side.
Discussion: As already pointed out, Hystrichokolpoma tumescens and H. mentitum described by McLean (1974), may have six postcingular paraplates. According to his figures of H. mentitum, McLean (1974) explains that if the left process of the pair in the parasulcal area is assigned to the
postcingular series, six postcingulars are identified, because many modern thecate dinoflagellates, especially the genus Gonyaulax, display a reduced 1"' plate where the intermediate process reflects the sixth postcingular paraplate. In the case of Hystrichokolpoma pacifica n. sp., the 1"' process is somewhat reduced and one intermediate hollow rectangular process is
recognized in the parasulcal area. But this process is not a postcingular member, because it occupies the position of the lower part of the parasulcal area and is not lying directly beneath the 6c process. This species, therefore, may originally have had five postcingular paraplates. The parasulcal region has three small processes, and each one may reflect right, intermediate (or
accessory) and left sulcal paraplatelets.
Comparison with similar species: Hystrichokolpoma pacifica n. sp. differs from H. poculum Maier 1959 in having quadrate bases of both large and small processes. It differs from H. salacina Eaton 1976 and H. mentitum McLean 1974 in lacking simple or branched slender, but characteristic
cingular processes with rectangular transversely expanded bases.
Dimensions:
Cyst, diameter: 51 (Holotype), 51-55 µm (Range)
Cyst, length: 55, 51-59 µm
Antapical process length: 30, 26-33 µm
Antapical process width: 20, 19-23 µm
Large processes, length: 21, 13-27 µm
Small processes, length: 15, 11-17 µm
Original description, Matsuoka, 1979.
Diagnosis: Cyst ellipsoidal with finely granulose surface. Processes composed of two types: large hollow, subconical to short cylindrical with rectangular or pentagonal base and entirely to slightly denticulate distal ends; in the paracingular region, small hollow processes with rectangular base expanded transversely.
Holotype: Slide no. OKD-3, position 4pIII, Plate I, 1--3. Kisembaru, KimSon, Kunigami-Gun, Okinawa Prefecture, Japan.
Paratype: Slide no. OKD-4, position 7GIII, Plate I, 4--5, Kisembaru, KimSon, Kunigami-Gun Okinawa Prefecture, Japan.
Description: The cyst is ellipsoidal in equatorial view and circular in polar view. Its wall is composed of two layers, the peri- and endophragms, and both are appressed between processes. The outer surface of the periphragm bears minute granules and indistinct striations. Processes formed from the periphragm reflect the paratabulation of 4'(?), 0a, 6", 6c, 5'", lp, 1as, lps, and 3s(?). The archeopyle is formed by loss of all apical series. Precingular, postcingular and antapical paraplates are represented by large hollow, subconical to short cylindrical processes with entirely to slightly denticulate distal extremities, which do not communicate with the endocoel. Processes 3" and 4" have five-sided bases, while others possess four-sided bases. Processes 3" and 6" are larger than other precingular processes, with the 1" process being the smallest. Each cingular paraplate has one small hollow process with a rectangular transversely expanded base and entirely to slightly
denticulate distal ends. The parasulcal region shows at least three small processes and two intermediate ones which may reflect original anterior and posterior sulcal plates. The paracingulum may be slightly displaced. The anterior sulcal process, intermediate in size and hollow with entirely or slightly denticulate distal ends, is situated between processes 1" and 6". An intermediate and hollow process with quadrate base is located between postcingular process 5'" and the posterior intercalary process. Owing to its size and position, this process probably represents the posterior sulcal, and not the sixth postcingular paraplate. Except for anterior and posterior sulcal process, three small processes with quadrate base and entirely to slightly denticulate distal extremities are observed in the parasulcal region. The postcingular process 1"' is the smallest among its series and all processes assigned to the postcingulum have quadrate bases. The antapical process with
pentagonal base is the largest, cylindrical in dorso-ventral view with the large triangular distal appendix observed on the dorsal side.
Discussion: As already pointed out, Hystrichokolpoma tumescens and H. mentitum described by McLean (1974), may have six postcingular paraplates. According to his figures of H. mentitum, McLean (1974) explains that if the left process of the pair in the parasulcal area is assigned to the
postcingular series, six postcingulars are identified, because many modern thecate dinoflagellates, especially the genus Gonyaulax, display a reduced 1"' plate where the intermediate process reflects the sixth postcingular paraplate. In the case of Hystrichokolpoma pacifica n. sp., the 1"' process is somewhat reduced and one intermediate hollow rectangular process is
recognized in the parasulcal area. But this process is not a postcingular member, because it occupies the position of the lower part of the parasulcal area and is not lying directly beneath the 6c process. This species, therefore, may originally have had five postcingular paraplates. The parasulcal region has three small processes, and each one may reflect right, intermediate (or
accessory) and left sulcal paraplatelets.
Comparison with similar species: Hystrichokolpoma pacifica n. sp. differs from H. poculum Maier 1959 in having quadrate bases of both large and small processes. It differs from H. salacina Eaton 1976 and H. mentitum McLean 1974 in lacking simple or branched slender, but characteristic
cingular processes with rectangular transversely expanded bases.
Dimensions:
Cyst, diameter: 51 (Holotype), 51-55 µm (Range)
Cyst, length: 55, 51-59 µm
Antapical process length: 30, 26-33 µm
Antapical process width: 20, 19-23 µm
Large processes, length: 21, 13-27 µm
Small processes, length: 15, 11-17 µm