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Achomosphaera callosa
Williams, Lentin and Fensome 1998 - Lentin and Williams Index of Fossil Dinoflagellates
Achomosphaera callosa, Matsuoka, 1983b, p. 128-129, pl.11, figs.6a–c,7a–b,8; text-figs.15A–B
Holotype: Matsuoka, 1983b, pl.11, figs.6a-c.
Locus typicus: Ota, Tsugawa-cho, Niigata Prefecture, Central Japan.
Stratum typicum: Tokonami Formation equivalent to the Nishiyama Formation - Pliocene.
Age: Pliocene
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Original description: [Matsuoka 1983, p. 128]:
Diagnosis:
Proximochorate cyst spherical to ovoidal and having thick wall. Surface of cyst coarsely granular Processes solid, hollow, bi- or trifurcate with bifid tips, and gonal only. Parasutural septa incomplete and occasionally visible. Archeopyle precingular and formed by displacement of the 3" paraplate.
Description:
The proximochorate intermediate to small cyst has thick wall and is spherical to ovoidal in shape. It consists of two layers, periphragm and endophragm adpressed between processes. The surface of the periphragm is coarsely granular.
Processes comprise gonal, solid, steady and bi- or trifurcate types sometimes with membraneous basal part. Their distal extremities are bifid. The surface of processes is smooth without any ornamentation. parasutural septa are hardly visible and are developed incompletely as Achomosphaera crassipellis (DEFLANDRE & COOKSON).
The archeopyle is a somewhat reduced precingular type made by loss of the 3'' paraplate and marks a pentagonal shape.
Dimensions:
Holotype; Length of cyst 44 µm, width of cyst 36 µm, thickness of wall ca. 2 µm, length of processes up to 13 µm.
Other specimens: Length of cyst 36-53 µm, width of cyst 36-45 µm, thickness of wall up to 3 µm, length of processes up to 15 µm. Number of specimens measured: 20.
Occurrence:
Rare to common in the Shiiya Formation, Nishiyama Formation and its equivalent formations, and Haizume Formation (Pliocene to Early Pleistocene).
Remarks:
Achomosphaera callosa sp. nov. closely resembles A. crassipellis (DEFLANDRE & COOKSON) and Spiniferites sp. cf. sagena shown by GOCHT (1969, P. 36, pl. 7, figs. 1, 2). The present species, however, differs from the latter two in possessing a coarsely granular periphragm, relatively elongate cyst body and only gonal processes. A. callosa can belong to the genus Achomosphaera on the basis of possession of incomplete parasutural septa as observed in A. crassipellis (DEFLANDRE & COOKSON).
Achomosphaera callosa, Matsuoka, 1983b, p. 128-129, pl.11, figs.6a–c,7a–b,8; text-figs.15A–B
Holotype: Matsuoka, 1983b, pl.11, figs.6a-c.
Locus typicus: Ota, Tsugawa-cho, Niigata Prefecture, Central Japan.
Stratum typicum: Tokonami Formation equivalent to the Nishiyama Formation - Pliocene.
Age: Pliocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Matsuoka 1983, p. 128]:
Diagnosis:
Proximochorate cyst spherical to ovoidal and having thick wall. Surface of cyst coarsely granular Processes solid, hollow, bi- or trifurcate with bifid tips, and gonal only. Parasutural septa incomplete and occasionally visible. Archeopyle precingular and formed by displacement of the 3" paraplate.
Description:
The proximochorate intermediate to small cyst has thick wall and is spherical to ovoidal in shape. It consists of two layers, periphragm and endophragm adpressed between processes. The surface of the periphragm is coarsely granular.
Processes comprise gonal, solid, steady and bi- or trifurcate types sometimes with membraneous basal part. Their distal extremities are bifid. The surface of processes is smooth without any ornamentation. parasutural septa are hardly visible and are developed incompletely as Achomosphaera crassipellis (DEFLANDRE & COOKSON).
The archeopyle is a somewhat reduced precingular type made by loss of the 3'' paraplate and marks a pentagonal shape.
Dimensions:
Holotype; Length of cyst 44 µm, width of cyst 36 µm, thickness of wall ca. 2 µm, length of processes up to 13 µm.
Other specimens: Length of cyst 36-53 µm, width of cyst 36-45 µm, thickness of wall up to 3 µm, length of processes up to 15 µm. Number of specimens measured: 20.
Occurrence:
Rare to common in the Shiiya Formation, Nishiyama Formation and its equivalent formations, and Haizume Formation (Pliocene to Early Pleistocene).
Remarks:
Achomosphaera callosa sp. nov. closely resembles A. crassipellis (DEFLANDRE & COOKSON) and Spiniferites sp. cf. sagena shown by GOCHT (1969, P. 36, pl. 7, figs. 1, 2). The present species, however, differs from the latter two in possessing a coarsely granular periphragm, relatively elongate cyst body and only gonal processes. A. callosa can belong to the genus Achomosphaera on the basis of possession of incomplete parasutural septa as observed in A. crassipellis (DEFLANDRE & COOKSON).