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Operculodinium echigoense
Operculodinium? echigoense Matsuoka, 1983
Originally Operculodinium, subsequently (and now) Operculodinium?. Mudie, 1987, questionably included this species in Operculodinium.
Taxonomic senior synonym: Operculodinium centrocarpum, according to Matsuoka et al. (1997, p.22).
Holotype: Matsuoka 1983, pl. 7, fig. 5.
Locus typicus: Minami-imogawa, Shitada-mura, Niigata Prefecture, Central Japan.
Stratum typicum: Nanatani Formation - early Middle Miocene.
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Original diagnosis: Matsuoka 1983, p. 126: Operculodinium echigoense
Intermediate cyst with reticulate or granular surface and spherical to ellipsoidal in shape Processes relatively long, slender and basically intratabular but apparently nontabular. Distal extremities small capitate or bifid. Precingular archeopyle simple. Operculum completely detached.
Original description: Matsuoka 1983, p. 126: Operculodinium echigoense
The subspherical to ellipsoidal chorate cysts consist of two layers, periphragm and endophragm adpressed between processes. The periphragm is not fibrous, but minutely reticulate or apparently granular. Processes with small bifid distal extremities are numerous, apparenty nontabular, hollow and slender. Except for the archeopyle, there is no ornamentation marking the paratabulation. The archeopyle is a simple precingular type judging from its trapezoidal shape and without any archeopyle suture.
Dimensions: Holotype: Cyst diameter 72 Ám, length of processes 12 Ám. Other specimens: Cyst diameter 67-86 Ám, length of processes 12-21 Ám. Number of specimens measured: 8.
Occurrence: Rare to abundant in the Nanatani Formation and its equivalent formations, Teradomari Formation and its equivalent formation and Shiiya Formation (late Early-to-early Middle Miocene to Late Miocene or younger).
Remarks: Matsuoka 1983, p. 126
This species can belong to the genus Operculodinium on the basis of the following characteristics; the periphragm is not fibrous but finely reticulate and processes are numerous, apparently nontabular and slender Operculodinium echigoense sp. nov. differs from other species in having larger cyst body, and relatively long, hollow and slender processes with small capitate or bifid distal extremities. Achomosphaera microtriaina (KLUMPP) SARJEANT, previously assigned to the genus Cordosphaeridium, is closely similar to the present species, but differs from the latter in possessing gonal and intergonal processes. Cordosphaeridium uncinispinosum described by DE CONINCK ( 1968, p. 32-33, pl. IX, figs. 6-8) may be assigned to this species on the basis of its large cyst body and process feature.
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Remark: Mudie 1987, p. 804, 805: ?Operculodinium echigoense
As described by Matsuoka (1983), this species is distinguished from O. centrocarpum by a finely reticulate or granular wall surface and relatively long, slender, hollow processes; illustrations of the paratypes (Matsuoka 1983, pl. 7, figs. 1-5) show, however, that the processes are relatively short compared with the main body diameter, and they appear to be structurally weak, hence aften vermiculate in appearance and frequently folded. All cysts from Sites 611 and 607 that were assigned to this taxon have apparently weak spines (see Plate 2, fig. 7), and are easily distinguished from O. centrocarpum, which normally has erect straight spines (see Plate 2, fig. 4). Matsuoka (1983) gives the range of E.echigoense as late early Miocene to late Miocene or younger.
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Supplemental description: McMinn, 1992, p.435
Large, ovoid cyst composed of a 2-3 Ám thick endophragm and a 1 Ám thick periphragm. Endophragm is smooth; periphragm is microreticulate and formed into nontabular processes. Process morphology is variable, most specimens have long, slender, acuminate to bifid processes, but other specimens have shorter processes with ragged distal terminations; intermediate forms are also present. Archeopyle is precingular, predominantly 1P, although a few specimens having 2P archaeopyle also have been observed; no other tabulation is indicated.
Originally Operculodinium, subsequently (and now) Operculodinium?. Mudie, 1987, questionably included this species in Operculodinium.
Taxonomic senior synonym: Operculodinium centrocarpum, according to Matsuoka et al. (1997, p.22).
Holotype: Matsuoka 1983, pl. 7, fig. 5.
Locus typicus: Minami-imogawa, Shitada-mura, Niigata Prefecture, Central Japan.
Stratum typicum: Nanatani Formation - early Middle Miocene.
---------------------------------------------------------
Original diagnosis: Matsuoka 1983, p. 126: Operculodinium echigoense
Intermediate cyst with reticulate or granular surface and spherical to ellipsoidal in shape Processes relatively long, slender and basically intratabular but apparently nontabular. Distal extremities small capitate or bifid. Precingular archeopyle simple. Operculum completely detached.
Original description: Matsuoka 1983, p. 126: Operculodinium echigoense
The subspherical to ellipsoidal chorate cysts consist of two layers, periphragm and endophragm adpressed between processes. The periphragm is not fibrous, but minutely reticulate or apparently granular. Processes with small bifid distal extremities are numerous, apparenty nontabular, hollow and slender. Except for the archeopyle, there is no ornamentation marking the paratabulation. The archeopyle is a simple precingular type judging from its trapezoidal shape and without any archeopyle suture.
Dimensions: Holotype: Cyst diameter 72 Ám, length of processes 12 Ám. Other specimens: Cyst diameter 67-86 Ám, length of processes 12-21 Ám. Number of specimens measured: 8.
Occurrence: Rare to abundant in the Nanatani Formation and its equivalent formations, Teradomari Formation and its equivalent formation and Shiiya Formation (late Early-to-early Middle Miocene to Late Miocene or younger).
Remarks: Matsuoka 1983, p. 126
This species can belong to the genus Operculodinium on the basis of the following characteristics; the periphragm is not fibrous but finely reticulate and processes are numerous, apparently nontabular and slender Operculodinium echigoense sp. nov. differs from other species in having larger cyst body, and relatively long, hollow and slender processes with small capitate or bifid distal extremities. Achomosphaera microtriaina (KLUMPP) SARJEANT, previously assigned to the genus Cordosphaeridium, is closely similar to the present species, but differs from the latter in possessing gonal and intergonal processes. Cordosphaeridium uncinispinosum described by DE CONINCK ( 1968, p. 32-33, pl. IX, figs. 6-8) may be assigned to this species on the basis of its large cyst body and process feature.
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Remark: Mudie 1987, p. 804, 805: ?Operculodinium echigoense
As described by Matsuoka (1983), this species is distinguished from O. centrocarpum by a finely reticulate or granular wall surface and relatively long, slender, hollow processes; illustrations of the paratypes (Matsuoka 1983, pl. 7, figs. 1-5) show, however, that the processes are relatively short compared with the main body diameter, and they appear to be structurally weak, hence aften vermiculate in appearance and frequently folded. All cysts from Sites 611 and 607 that were assigned to this taxon have apparently weak spines (see Plate 2, fig. 7), and are easily distinguished from O. centrocarpum, which normally has erect straight spines (see Plate 2, fig. 4). Matsuoka (1983) gives the range of E.echigoense as late early Miocene to late Miocene or younger.
-------------------------------------------------------------
Supplemental description: McMinn, 1992, p.435
Large, ovoid cyst composed of a 2-3 Ám thick endophragm and a 1 Ám thick periphragm. Endophragm is smooth; periphragm is microreticulate and formed into nontabular processes. Process morphology is variable, most specimens have long, slender, acuminate to bifid processes, but other specimens have shorter processes with ragged distal terminations; intermediate forms are also present. Archeopyle is precingular, predominantly 1P, although a few specimens having 2P archaeopyle also have been observed; no other tabulation is indicated.