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Meiourogonyaulax viriosa
Meiourogonyaulax viriosa Riding and Helby, 2001d, p.87,89, figs.13A-L.
Holotype: Riding and Helby, 2001d, figs.13K.
Age: late Callovian.
Original description (Riding & Helby, 2001d):
Meiourogonyaulax viriosa sp. nov.
Previous Australian usage
M.P. 70 – Helby.
Meiourogonyaulax sp. 70 – Helby.
Meiourogonyaulax bulloidea (pars.) – Morgan.
Description: A species of Meiourogonyaulax ellipsoidal to subcircular in dorsoventral outline. A small, rounded, solid apical boss-like protuberance may be present on the operculum. Paratabulation fully indicated by low parasutural crests which are normally distally smooth. The parasutural crests are slender to relatively wide. They are continuous and generally entire, however, slim, fenestrate crests are present and rarely these may be irregularly denticulate distally. The crests are highest at gonal points where they may be thickened into short projections. The paracingulum is not subdivided into paraplates, however, the antapical end of the strongly indented parasulus may occasionally exhibit internal parasutural crests. Autophragm thick, robust, microreticulate; occasionally partially microgranulate and/or microscabrate. One or more dark, subcircular accumulation bodies are normally present inside the cyst body.
Dimensions (µm, n=37) including crests where appropriate; Min.(Mean)Max.
Length of cyst incl. operculum: 62(74)99
Length of cyst excl. operculum: 46(64)79
Width of cyst: 47(67)93
Height of parasutural crests: 1(2.5)5
The measured specimemens are from sidewall core samples in Challs-11 ST2 we;; (1842.00m), Rowan-1 ST well (3181.00m and 3183.00m), Tern-1 well (1528.28m and 1529.50m) and Tern-2 well (1459.20m), a conventional core sample at 1642.50m from Jabiru-1 well and ditch cuttings between 1530.11m and 1536.21m in Tern-2 well.
Comments: Meiourogonyaulax viriosa is variable in outline; it may be elongate, however, many specimens are wide and squat. Furthermore, the apical protuberance, when developed, helps to impart a flat cone shape to the operculum. The apical boss or protuberance is solid and typically low in height (1 µm – 3 µm) and broad (up to 6 µm). A characteristic feature of this taxon is the thick Autophragm, which is consistently microreticulate and occasionally partially microgranulate and/or microscabrate. The fenestrae are normally less than 1 µm in diameter, however, occasionally some attain 1 µm in width. The autophragm does not bear intratabular ornamentation, apart from the small fenestrae and microgranules/microscabrae, and varies between 1 and 2 µm in thickness. Because of the robust nature of the autophragm, the species does not tend to fold. However, mechanical damage may cause the autophragm to break, normally along parasutures, and damaged (crushed) specimens may be anomalously wide because of this. The parasutural ornamentation is also somewhat variable, but typically comprises slender (1 < µm) to relatively broad (up to 3 µm), continuous crests, which are normally smooth distally. The rare, thin, fenestrate and occasionally distally irregularly denticulate parasutural crests suggests that the parasutural ornamentation may be formed from a dense network of coalescing processes. The parasutural crests are highest at gonal points and around the antapical (1’’’’) paraplate and lowest in the apical region. As indicated in Dimensions above, there is considerable variation in size.
Comparison: Meiourogonyaulax viriosa closely resembles M. bulloidea but differs in not being granulate and in lacking the intratabular ridges and the distinctive intratabular bosses that characterize the type material of the latter (Riding & Helby, this volume). Meiourogonyaulax viriosa also shows similarities to M. penitabulata and Lithodinia protothymosa, with which it co-occurs and is presumably closely related. However, M. viriosa lacks penitabular ornamentation and major intratabular elements. This new form is also similar to several previously described species with distally smooth parasutural crests or ridges. These include M. bulloidea, M. pertusa, M. planoseptata and M. stoveri. However, these taxa all lack the variable parasutural crests which are characteristic of M. viriosa.
Derivation of name: From the Latin viriosus, meaning robust or strong, and referring to the thick autophragm of this species.
Holotype and type locality: Fig. 13K, CPC 35439, Tern-1 well, sidewall core sample at 1528.28m.
Stratigraphical distribution: Meiourogonyaulax viriosa has been recorded from the late Callovian strata of the Timor Sea region, occurring sporadically in the Wanaea digitate Zone (7bi) and consistently throughout the Rigaudella aemula Zone (7a) (Foster, this volume; Helby and partridge, in prep.)
Holotype: Riding and Helby, 2001d, figs.13K.
Age: late Callovian.
Original description (Riding & Helby, 2001d):
Meiourogonyaulax viriosa sp. nov.
Previous Australian usage
M.P. 70 – Helby.
Meiourogonyaulax sp. 70 – Helby.
Meiourogonyaulax bulloidea (pars.) – Morgan.
Description: A species of Meiourogonyaulax ellipsoidal to subcircular in dorsoventral outline. A small, rounded, solid apical boss-like protuberance may be present on the operculum. Paratabulation fully indicated by low parasutural crests which are normally distally smooth. The parasutural crests are slender to relatively wide. They are continuous and generally entire, however, slim, fenestrate crests are present and rarely these may be irregularly denticulate distally. The crests are highest at gonal points where they may be thickened into short projections. The paracingulum is not subdivided into paraplates, however, the antapical end of the strongly indented parasulus may occasionally exhibit internal parasutural crests. Autophragm thick, robust, microreticulate; occasionally partially microgranulate and/or microscabrate. One or more dark, subcircular accumulation bodies are normally present inside the cyst body.
Dimensions (µm, n=37) including crests where appropriate; Min.(Mean)Max.
Length of cyst incl. operculum: 62(74)99
Length of cyst excl. operculum: 46(64)79
Width of cyst: 47(67)93
Height of parasutural crests: 1(2.5)5
The measured specimemens are from sidewall core samples in Challs-11 ST2 we;; (1842.00m), Rowan-1 ST well (3181.00m and 3183.00m), Tern-1 well (1528.28m and 1529.50m) and Tern-2 well (1459.20m), a conventional core sample at 1642.50m from Jabiru-1 well and ditch cuttings between 1530.11m and 1536.21m in Tern-2 well.
Comments: Meiourogonyaulax viriosa is variable in outline; it may be elongate, however, many specimens are wide and squat. Furthermore, the apical protuberance, when developed, helps to impart a flat cone shape to the operculum. The apical boss or protuberance is solid and typically low in height (1 µm – 3 µm) and broad (up to 6 µm). A characteristic feature of this taxon is the thick Autophragm, which is consistently microreticulate and occasionally partially microgranulate and/or microscabrate. The fenestrae are normally less than 1 µm in diameter, however, occasionally some attain 1 µm in width. The autophragm does not bear intratabular ornamentation, apart from the small fenestrae and microgranules/microscabrae, and varies between 1 and 2 µm in thickness. Because of the robust nature of the autophragm, the species does not tend to fold. However, mechanical damage may cause the autophragm to break, normally along parasutures, and damaged (crushed) specimens may be anomalously wide because of this. The parasutural ornamentation is also somewhat variable, but typically comprises slender (1 < µm) to relatively broad (up to 3 µm), continuous crests, which are normally smooth distally. The rare, thin, fenestrate and occasionally distally irregularly denticulate parasutural crests suggests that the parasutural ornamentation may be formed from a dense network of coalescing processes. The parasutural crests are highest at gonal points and around the antapical (1’’’’) paraplate and lowest in the apical region. As indicated in Dimensions above, there is considerable variation in size.
Comparison: Meiourogonyaulax viriosa closely resembles M. bulloidea but differs in not being granulate and in lacking the intratabular ridges and the distinctive intratabular bosses that characterize the type material of the latter (Riding & Helby, this volume). Meiourogonyaulax viriosa also shows similarities to M. penitabulata and Lithodinia protothymosa, with which it co-occurs and is presumably closely related. However, M. viriosa lacks penitabular ornamentation and major intratabular elements. This new form is also similar to several previously described species with distally smooth parasutural crests or ridges. These include M. bulloidea, M. pertusa, M. planoseptata and M. stoveri. However, these taxa all lack the variable parasutural crests which are characteristic of M. viriosa.
Derivation of name: From the Latin viriosus, meaning robust or strong, and referring to the thick autophragm of this species.
Holotype and type locality: Fig. 13K, CPC 35439, Tern-1 well, sidewall core sample at 1528.28m.
Stratigraphical distribution: Meiourogonyaulax viriosa has been recorded from the late Callovian strata of the Timor Sea region, occurring sporadically in the Wanaea digitate Zone (7bi) and consistently throughout the Rigaudella aemula Zone (7a) (Foster, this volume; Helby and partridge, in prep.)