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Mendicodinium scabratum
Mendicodinium scabratum Riding and Helby, 2001a, p.7,9, figs.5A-I.
Holotype: Riding and Helby, 2001a, figs.5D-F.
Age: Toarcian-Bajocian.
Original description (Riding and Helby, 2001a):
Description. A proximate Mendicodinium of intermediate size and ellipsoidal dorsoventral outline. The hypocyst is frequently larger than the epicyst. Paraplate 1”” is normally slightly concave or flattened. The cyst is normally slightly wider than long. The autophragm is of moderate thickness and scabrate, microscabrate or granulate. The paracingulum may be faintly indicated on the hypocyst by a low parasutural ridge or a lineation of ornamentation. There may also be a slight inset or concavity at the paracingulum.
Dimensions (µm, n=30): Min. (Mean) Max.
Length: 41 (52) 67
Width: 45 (54) 62
The measured specimens are from sidewall core samples in Skua-5 (2646.00m) and Skua-6 (2385.00m and 2391.50m) wells.
Comments. Mendicodinium scabratum typically has a scabrate autophragm, but microscabrate or granulate individuals have been recorded. The type and density of ornamentation in this species is somewhat variable. Occasionally, the paracingulum is faintly indicated on the hypocyst by a low parasutural ridge or lineation of ornament and may also be marked by a slight indentation or concavity. The relatively high size range in the cyst body dimensions is due to the occurrence of ‘open-lid’ preservational style.
Comparison. Mendicodinium scabratum is similar to several members of the plexus of smalle Mendicodinium described from the Toarcian of central Italy by Bucefalo Palliani et al. (1997b). These are M. brunneum, M. microscabratum and M. umbriense, none of which exceeds 38 µm in width (Bucefalo Palliani et al., 1997b); they are all significantly smaller than M. scabratum. Mendicodinium brunneum has a thick autophragm and is granulate. The cyst wall of M. microscabratum Bucefalo Palliani et al. 1997 varies from smooth to microscabrate, and the autophragm of Mendicodinium umbriense is characterized by relatively large granules. Mendicodinium reticulatum Morgenroth 1980, the genotype, is also small but it differs from M. scabratum in having a coarsely reticulate autophragm. The seven remaining validly described species of Mendicodinium listed by Willams et al. (1998, p. 397-398) are all significantly larger in size and, incidentally, younger than M. scabratum. Mendicodinium caperatum Brideaux 1977 and M. granulatum Kumar 1986 are both scabrate/granulate. Two Mid to Late Jurassic species Mendicodinium groenlandicum (Pocock & Sarjeant 1970) Davey 1979 and M. quadratum Kumar 1987 have characteristically psilate autophragms. The autophragm of M. kemperi Heilmann-Clausen (in Heilmann-Clausen & Thomsen 1995) is ornamented by thin discontinuous ridges, rugulae and granules. Mendicodinium microreticulatum Kumar 1986 and Mendicodinium morgenrothum Butler 1995 have microreticulate and verrucate autophragms respectively.
Derivation of name. From the Latin scabra, meaning rough.
Holotype and type locality. Figs 5D-F, CPC 35131, Skua-5 well sidewall core sample at 2646.00m.
Stratigraphical distribution. See Appendix 1 and Fig. 12. Mendicodinium scabratum also ranges into Aalenian/Bajocian strata which are referable to the upper Callialasporites turbatus Oppel Zone equivalent of Helby et al. (1987) (Oliver-1 ell at 3057.00m, see Appendix 1).
Holotype: Riding and Helby, 2001a, figs.5D-F.
Age: Toarcian-Bajocian.
Original description (Riding and Helby, 2001a):
Description. A proximate Mendicodinium of intermediate size and ellipsoidal dorsoventral outline. The hypocyst is frequently larger than the epicyst. Paraplate 1”” is normally slightly concave or flattened. The cyst is normally slightly wider than long. The autophragm is of moderate thickness and scabrate, microscabrate or granulate. The paracingulum may be faintly indicated on the hypocyst by a low parasutural ridge or a lineation of ornamentation. There may also be a slight inset or concavity at the paracingulum.
Dimensions (µm, n=30): Min. (Mean) Max.
Length: 41 (52) 67
Width: 45 (54) 62
The measured specimens are from sidewall core samples in Skua-5 (2646.00m) and Skua-6 (2385.00m and 2391.50m) wells.
Comments. Mendicodinium scabratum typically has a scabrate autophragm, but microscabrate or granulate individuals have been recorded. The type and density of ornamentation in this species is somewhat variable. Occasionally, the paracingulum is faintly indicated on the hypocyst by a low parasutural ridge or lineation of ornament and may also be marked by a slight indentation or concavity. The relatively high size range in the cyst body dimensions is due to the occurrence of ‘open-lid’ preservational style.
Comparison. Mendicodinium scabratum is similar to several members of the plexus of smalle Mendicodinium described from the Toarcian of central Italy by Bucefalo Palliani et al. (1997b). These are M. brunneum, M. microscabratum and M. umbriense, none of which exceeds 38 µm in width (Bucefalo Palliani et al., 1997b); they are all significantly smaller than M. scabratum. Mendicodinium brunneum has a thick autophragm and is granulate. The cyst wall of M. microscabratum Bucefalo Palliani et al. 1997 varies from smooth to microscabrate, and the autophragm of Mendicodinium umbriense is characterized by relatively large granules. Mendicodinium reticulatum Morgenroth 1980, the genotype, is also small but it differs from M. scabratum in having a coarsely reticulate autophragm. The seven remaining validly described species of Mendicodinium listed by Willams et al. (1998, p. 397-398) are all significantly larger in size and, incidentally, younger than M. scabratum. Mendicodinium caperatum Brideaux 1977 and M. granulatum Kumar 1986 are both scabrate/granulate. Two Mid to Late Jurassic species Mendicodinium groenlandicum (Pocock & Sarjeant 1970) Davey 1979 and M. quadratum Kumar 1987 have characteristically psilate autophragms. The autophragm of M. kemperi Heilmann-Clausen (in Heilmann-Clausen & Thomsen 1995) is ornamented by thin discontinuous ridges, rugulae and granules. Mendicodinium microreticulatum Kumar 1986 and Mendicodinium morgenrothum Butler 1995 have microreticulate and verrucate autophragms respectively.
Derivation of name. From the Latin scabra, meaning rough.
Holotype and type locality. Figs 5D-F, CPC 35131, Skua-5 well sidewall core sample at 2646.00m.
Stratigraphical distribution. See Appendix 1 and Fig. 12. Mendicodinium scabratum also ranges into Aalenian/Bajocian strata which are referable to the upper Callialasporites turbatus Oppel Zone equivalent of Helby et al. (1987) (Oliver-1 ell at 3057.00m, see Appendix 1).