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Operculodinium vacuolatum
Operculodinium vacuolatum Head et al., 1989
Holotype: Head et al., 1989, pl.9, figs.8-9
Age: Middle or early Late? Miocene
Original description (Head et al., 1989):
Operculodinium vacuolatum n. sp. (Pl. 9, Figs. 8,9)
?Operculodinium centrocarpum (Deflandre and Cookson, 1955) Wall, 1967; (in part) Turon and Londeix, 1988, Pl. 4, Figs. 6 through 8 only.
Holotype (Pl. 9, Figs. 8,9). Sample 105-645E-40R-4, 28-33 cm, (5) W5/0; middle or early late? Miocene.
Derivation of name. From French, vacuole, little vacuum; from Latin, vacuum, an empty space; named with reference to the vacuolate nature of the periphragm and processes.
Diagnosis. Cysts closely appressed biphragmal, proximochorate, spherical to broadly elipsoidal. Endophragm very thin. Periphragm thicker than endophragm and vacuolate, appearing microreticulate, or occasionally microvermiculate in surface view. Periphragm bears low verrucae or bacculae that are vacuolate and have a nontabular distribution. Archeopyle precingular Type P. Operculum free.
Dimensions. Holotype: maximum diameter (excluding processes), 34 µm, process length, 1.5 µm. Range in maximum diameter, 33 (38.4) 50 µm. Wall is 1.0 to 1.5 µm thick. Processes range from 1.0 to 2.5 µm long. Fourteen specimens were measured.
Description. The endophragm is thinner than the periphragm and is often barely discernible. The periphragm usually appears microreticulate in plain view, with lacunae of 0.5 to 1.0 µm in diameter and muri 0.2 /tm wide, although it may appear microvermiculate in some specimens. This pattern is apparently a subsurface feature, reflecting the vacuolate nature of the periphragm, which is just discernible in optical section under bright field microscopy. Processes take the form of verrucae or bacculae and have a diameter of about 2.0 µm and are 1.0 to 2.5 µm long. These processes are rounded distally, although they may be roundly truncated, and are vacuolate. They have a regular distribution over the entire surface of the cyst and are spaced approximately 1 to 4 µm apart. The archeopyle is precingular, apparently Type P3" . There is no other expression of paratabulation. O. vacuolatum n. sp. was recovered from a single sample, where it occurs abundantly. Critical observations of the wall structure could be made only for a small proportion of the cyst population, since in many specimens the cellosize mounting medium used in this study had not penetrated the small cavities occurring within the periphragm and processes.
Remarks. This species is distinguished from other species of Operculodinium by its short processes and the vacuolate nature of its periphragm and processes. An apparently similar specimen was recorded by Turon and Londeix (1988) as "Operculodinium centrocarpum (Deflandre and Cookson, 1955) Wall, 1967; Pl. 4, Figs. 6-8—specimen with reduced processes" from the late Holocene of the western Mediterranean Sea.
Holotype: Head et al., 1989, pl.9, figs.8-9
Age: Middle or early Late? Miocene
Original description (Head et al., 1989):
Operculodinium vacuolatum n. sp. (Pl. 9, Figs. 8,9)
?Operculodinium centrocarpum (Deflandre and Cookson, 1955) Wall, 1967; (in part) Turon and Londeix, 1988, Pl. 4, Figs. 6 through 8 only.
Holotype (Pl. 9, Figs. 8,9). Sample 105-645E-40R-4, 28-33 cm, (5) W5/0; middle or early late? Miocene.
Derivation of name. From French, vacuole, little vacuum; from Latin, vacuum, an empty space; named with reference to the vacuolate nature of the periphragm and processes.
Diagnosis. Cysts closely appressed biphragmal, proximochorate, spherical to broadly elipsoidal. Endophragm very thin. Periphragm thicker than endophragm and vacuolate, appearing microreticulate, or occasionally microvermiculate in surface view. Periphragm bears low verrucae or bacculae that are vacuolate and have a nontabular distribution. Archeopyle precingular Type P. Operculum free.
Dimensions. Holotype: maximum diameter (excluding processes), 34 µm, process length, 1.5 µm. Range in maximum diameter, 33 (38.4) 50 µm. Wall is 1.0 to 1.5 µm thick. Processes range from 1.0 to 2.5 µm long. Fourteen specimens were measured.
Description. The endophragm is thinner than the periphragm and is often barely discernible. The periphragm usually appears microreticulate in plain view, with lacunae of 0.5 to 1.0 µm in diameter and muri 0.2 /tm wide, although it may appear microvermiculate in some specimens. This pattern is apparently a subsurface feature, reflecting the vacuolate nature of the periphragm, which is just discernible in optical section under bright field microscopy. Processes take the form of verrucae or bacculae and have a diameter of about 2.0 µm and are 1.0 to 2.5 µm long. These processes are rounded distally, although they may be roundly truncated, and are vacuolate. They have a regular distribution over the entire surface of the cyst and are spaced approximately 1 to 4 µm apart. The archeopyle is precingular, apparently Type P3" . There is no other expression of paratabulation. O. vacuolatum n. sp. was recovered from a single sample, where it occurs abundantly. Critical observations of the wall structure could be made only for a small proportion of the cyst population, since in many specimens the cellosize mounting medium used in this study had not penetrated the small cavities occurring within the periphragm and processes.
Remarks. This species is distinguished from other species of Operculodinium by its short processes and the vacuolate nature of its periphragm and processes. An apparently similar specimen was recorded by Turon and Londeix (1988) as "Operculodinium centrocarpum (Deflandre and Cookson, 1955) Wall, 1967; Pl. 4, Figs. 6-8—specimen with reduced processes" from the late Holocene of the western Mediterranean Sea.