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Cribroperidinium volkovae
Cribroperidinium volkovae Iosifova 1996
Holotype: Iosifova 1996: Plate II, 6a,b; Fig. 6
Isotype: Iosifova 1996: Plate II, 4
Locus typicus: Tchernaya Retchka outcrop, the Ryazan district, Russia.
Stratum typicum: deposits of probable Hauterivian age.
Diagnosis: Iosifova 1996, p. 215, 217, 219
A species of Cribroperidinium with short apical horn, acavate. Wall two-layered, endophragm thin, periphragm thick, spongious. Tubercles and any other positive sculptural elements are absent.
Dimensions: Length: holotype: 81Ám, range: 81-85Ám; width: holotype: 75Ám, range: 75-81Ám. Four specimens measured.
Description: Iosifova 1996, p. 215, 217, 219
Cysts proximate, subspherical, acavate, with a small truncated horn (length 5-6Ám). Wall thick (thickness about 5 llm), consists of thin endophragm and thick spongious (in optical section) periphragm. Endophragm and periphragm closely adpressed over the whole surface. Surface of the cyst strongly perforated. Tubercles and any other positive sculptural elements are absent on the bodies of paraplates. Apical horn is formed by periphragm only. Paratabulation cribroperidinioid, 4", 6", 6c, 6"", lp, lpp, 1"". Ventral paratabulation L-type: 6" contacts with 4" and 1". 1" and 4" narrow, elongate, 6" small, pentagonal. 1"" and 6"" elongate, quadrangular. Suture 4""/5"" situated mid-dorsally. 1"" small, asymmetric. Additional ridges present on the bodies of paraplates 5"-6", 2""-5"". Paracingulum narrow (width 1.5Ám), helicoidal, laevorotatory, the ends being displaced at the parasulcus by approximately three paracingulum width. Parasulcus distinct. Paraplates lp and lpp narrow, curved. Ridges are low, but distinct, with entire margins, perforated. Archeopyle precingular, Type 3".
Comparison: It differs from all other species of the genus by the combination of short apical horn and perforated periphragm without any positive sculptural elements on the bodies of paraplates. C. tensiftense Below, 1981 has also a small apical horn and perforated periphragm, but differs from the new species by the presence of pilae, baculae and tubercles on the bodies of paraplates. In addition, paraplate 1"" of C. tensiftense is triangular. Other species of Cribroperidinium with perforated periphragm have much longer apical horn. The new species resembles C. sepimentum Neale and Sarjeant, 1962 by both perforated periphragm and ridges, but differs from it by much smaller apical horn. In addition, C. volkovae Iosifova, sp. nov. has narrow paraplate 6", its wall is much thicker and ridges are much lower. C. volkovae Iosifova, sp. nov. resembles C. janinae Gorka, 1982 by its short apical horn, but differs from it by its perforated periphragm.
Occurrence: Tchernaya Retchka outcrop, the Ryazanian, R. riasanensis ammonite zone and deposits of probable Hauterivian age.
Holotype: Iosifova 1996: Plate II, 6a,b; Fig. 6
Isotype: Iosifova 1996: Plate II, 4
Locus typicus: Tchernaya Retchka outcrop, the Ryazan district, Russia.
Stratum typicum: deposits of probable Hauterivian age.
Diagnosis: Iosifova 1996, p. 215, 217, 219
A species of Cribroperidinium with short apical horn, acavate. Wall two-layered, endophragm thin, periphragm thick, spongious. Tubercles and any other positive sculptural elements are absent.
Dimensions: Length: holotype: 81Ám, range: 81-85Ám; width: holotype: 75Ám, range: 75-81Ám. Four specimens measured.
Description: Iosifova 1996, p. 215, 217, 219
Cysts proximate, subspherical, acavate, with a small truncated horn (length 5-6Ám). Wall thick (thickness about 5 llm), consists of thin endophragm and thick spongious (in optical section) periphragm. Endophragm and periphragm closely adpressed over the whole surface. Surface of the cyst strongly perforated. Tubercles and any other positive sculptural elements are absent on the bodies of paraplates. Apical horn is formed by periphragm only. Paratabulation cribroperidinioid, 4", 6", 6c, 6"", lp, lpp, 1"". Ventral paratabulation L-type: 6" contacts with 4" and 1". 1" and 4" narrow, elongate, 6" small, pentagonal. 1"" and 6"" elongate, quadrangular. Suture 4""/5"" situated mid-dorsally. 1"" small, asymmetric. Additional ridges present on the bodies of paraplates 5"-6", 2""-5"". Paracingulum narrow (width 1.5Ám), helicoidal, laevorotatory, the ends being displaced at the parasulcus by approximately three paracingulum width. Parasulcus distinct. Paraplates lp and lpp narrow, curved. Ridges are low, but distinct, with entire margins, perforated. Archeopyle precingular, Type 3".
Comparison: It differs from all other species of the genus by the combination of short apical horn and perforated periphragm without any positive sculptural elements on the bodies of paraplates. C. tensiftense Below, 1981 has also a small apical horn and perforated periphragm, but differs from the new species by the presence of pilae, baculae and tubercles on the bodies of paraplates. In addition, paraplate 1"" of C. tensiftense is triangular. Other species of Cribroperidinium with perforated periphragm have much longer apical horn. The new species resembles C. sepimentum Neale and Sarjeant, 1962 by both perforated periphragm and ridges, but differs from it by much smaller apical horn. In addition, C. volkovae Iosifova, sp. nov. has narrow paraplate 6", its wall is much thicker and ridges are much lower. C. volkovae Iosifova, sp. nov. resembles C. janinae Gorka, 1982 by its short apical horn, but differs from it by its perforated periphragm.
Occurrence: Tchernaya Retchka outcrop, the Ryazanian, R. riasanensis ammonite zone and deposits of probable Hauterivian age.