Back
Alterbia distincta
Alterbia? distincta, (Wilson, 1967), Lentin and Williams, 1976
Now Alterbidinium?. Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly Alterbia? (combination illegitimate), fourthly (and now) Alterbidinium?. Stover and Evitt (1978, p.93) considered this to be a provisionally accepted species of Alterbia.
Holotype: Wilson, 1967, fig.9
Locus typicus: Erratics near Minna Bluff, McMurdo Sound, Antarctica
Stratum typicum: Early Tertiary
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Deflandrea distincta: [Wilson, 1967, p. 63-64]:
Description:
Test bi- layered, dorso- ventrally flattened, elongate, bilaterally asymmetric. Inner layer radially contracted forming fairly thick- walled, dense, smooth, circular internal cyst. Outer layer conspicuously folded, especially on the ventral surface; the linear folds extend from the apex to each antapical horn; surface of outer cyst finely granulate and epithecal margin forms membranous shoulder- like flange. Prominent blunt- ended apical horn wide at base and narrow at top (l = 27-33 µm) and well developed pointed right antapical horn (l = 16-20 µm); left antapical horn small (l = 5-8 µm). Laevo- rotatory transverse girdle present. Depressed area between longitudinal folds o ventral hypotheca indicative of longitudinal furrow.
Archeopyle more or less trapezium- shaped, intercalary, dorsal; operculum fixed by posterior margin to shell. Atabulate.
Dimensions:
Holotype l = 118 µm, b = 61 µm, dimensions of inner cyst (58x63) µm.
Range l = 96(106)118 µm, b = 58(64)77 µm (7 specimens).
Affinities/Discussion:
Deflandrea distincta shares certain features with D. macmurdoensis and D. asymmetrica, especially the pronounced bilateral asymmetry, the blunt apical horn, and the unusual type of archeopyle. However, in Deflandrea macmurdoensis the surface of the outer cyst is adorned with spines or spiny ridges, whereas the only forms of ornamentation of the other two species are the conspicuous folds, especially prominent on the ventral surface. D. distincta differs from D. asymmetrica in having a much larger outer cyst, relatively narrower and more pointed horns, finely granulate sculpturing, more angular archeopyle and a relatively smaller and thicker-walled inner cyst. The species was recorded as Deflandrea aff. pirnaensis in the preliminary species list of McIntyre and Wilson, 1966. A somewhat similar type of archeopyle has been illustrated by Evitt in an unnamed species of Deflandrea (Evitt, 1961).
Now Alterbidinium?. Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly Alterbia? (combination illegitimate), fourthly (and now) Alterbidinium?. Stover and Evitt (1978, p.93) considered this to be a provisionally accepted species of Alterbia.
Holotype: Wilson, 1967, fig.9
Locus typicus: Erratics near Minna Bluff, McMurdo Sound, Antarctica
Stratum typicum: Early Tertiary
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Deflandrea distincta: [Wilson, 1967, p. 63-64]:
Description:
Test bi- layered, dorso- ventrally flattened, elongate, bilaterally asymmetric. Inner layer radially contracted forming fairly thick- walled, dense, smooth, circular internal cyst. Outer layer conspicuously folded, especially on the ventral surface; the linear folds extend from the apex to each antapical horn; surface of outer cyst finely granulate and epithecal margin forms membranous shoulder- like flange. Prominent blunt- ended apical horn wide at base and narrow at top (l = 27-33 µm) and well developed pointed right antapical horn (l = 16-20 µm); left antapical horn small (l = 5-8 µm). Laevo- rotatory transverse girdle present. Depressed area between longitudinal folds o ventral hypotheca indicative of longitudinal furrow.
Archeopyle more or less trapezium- shaped, intercalary, dorsal; operculum fixed by posterior margin to shell. Atabulate.
Dimensions:
Holotype l = 118 µm, b = 61 µm, dimensions of inner cyst (58x63) µm.
Range l = 96(106)118 µm, b = 58(64)77 µm (7 specimens).
Affinities/Discussion:
Deflandrea distincta shares certain features with D. macmurdoensis and D. asymmetrica, especially the pronounced bilateral asymmetry, the blunt apical horn, and the unusual type of archeopyle. However, in Deflandrea macmurdoensis the surface of the outer cyst is adorned with spines or spiny ridges, whereas the only forms of ornamentation of the other two species are the conspicuous folds, especially prominent on the ventral surface. D. distincta differs from D. asymmetrica in having a much larger outer cyst, relatively narrower and more pointed horns, finely granulate sculpturing, more angular archeopyle and a relatively smaller and thicker-walled inner cyst. The species was recorded as Deflandrea aff. pirnaensis in the preliminary species list of McIntyre and Wilson, 1966. A somewhat similar type of archeopyle has been illustrated by Evitt in an unnamed species of Deflandrea (Evitt, 1961).