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Alterbidinium acutulum
Alterbidinium acutulum, (Wilson, 1967), Lentin and Williams, 1985; Emendation as Alterbidinium acutulum: Khowaja-Ateequzzaman et al., 1991, p. 41-42
Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly (and now) Alterbidinium. Taxonomic junior synonyms: Albertia recticornis, according to Whitney (1979, p.125) and Lentin and Williams (1993, p.14); Albertia curvicornis, according to Whitney (1979, p.125). The nomenclatural type of the genus Alterbidinium remains the holotype of Alterbidinium recticorne.
Tax. sr. synonym of Alterbia curvicornis (Vozzhennikova, 1967) Lentin and Williams, 1976, according to Whitney, 1979.
Holotype: Wilson, 1967, fig.12
Locus typicus: Campbell Island, New Zealand
Stratum typicum: ?Teurian, Palaeocene
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Original description as Deflandrea acutula: [Wilson, 1967, p. 225-226]:
Description:
Test narrow, bi-layered, comprising smooth outer cyst tapering at poles, and smaller inner cyst. Right antapical horn long (l=14-36 µm), pointed. Left antapical horn absent, but position represented by minor angularity in margin of outer cyst.
Archaeopyle long, narrow, intercalary, situated on dorsal epitheca; operculum hinged to shell by posterior margin.
Spiral transverse girdle represented by a folding of outer cyst.
Dimensions:
Holotype: l=83 µm, b=44 µm, inner cyst 44x36 µm.
Two other measured specimens: SM 621: l=116 µm, b=47 µm, inner cyst 47x39 µm; SM 602: l=94 µm, b=50 µm, inner cyst=44x41 µm.
Affinities:
D. acutula shares certain features with several Antarctic species of Deflandrea described recently by the author (Wilson, 1967). In particular the archaeopyle resembles that of D. asymmetrica and D. distincta, although it is much narrower. All three species possess a flat-tipped apical horn. D. acutula is distinguished from the two Antarctic species by its different shell outline, greater development of the right antapical horn, and the absence of a left antapical horn.
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Emended description as Alterbidinium acutulum:
Khowaja et al., 1991. p. 42-44:
Diagnosis:
Cyst proximate, dorsoventrally compressed, circumcavate; pericyst ambitus pentagonal with an apical and two symmetrically placed unequal antapical horns, right antapical horn reduced; periphragm thin, smooth, endocyst subpentagonal, endophragm thicker than periphragm, smooth, periparacingulum present, annulate; paratabulation indicated by archaeopyle and periparacingulum only; archaeopyle intercalary, independently developed on periphragm and endophragm; periarchaeopyle hexa 2a, isodeltaform, perioperculum adnate; endoarchaeopyle hexa 2a, eury-deltaform, endoperculum adnate.
Description:
Shape: Cyst proximate, dorso-ventrally compressed; pericyst ambitus pentagonal with a broad based apical horn and two symmetrically placed unequal antapical horns, right antapical horn reduced; endocyst subpentagonal.
Wall relationship: Apical and antapical pericoels connected through ambital pericoel (circumcavate); endocyst shifted more towards dorsal side where the periphragm and endophragm are appressed in precingular and postcingular areas.
Wall features: No parasutural features; periphragm and endophragm thin but endophragm thicker than periphragm; periparacingulum, annulate running high over endocyst, marked by two parallel ridges and a furrow in between; periparasulcus marked by a depression.
Paratabulation: Indicated by archaeopyle and periparacingulum only.
Archaeopyle: Intercalary, independently developed on periphragm and endophragm; periarchaeopyle hexa 2a, iso-deltaform, perioperculum adnate (adnation along adcingular margin); endoarchaeopyle hexa 2a, eury-deltaform, endoperculum adnate (adnation along adcingular margin ).
Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly (and now) Alterbidinium. Taxonomic junior synonyms: Albertia recticornis, according to Whitney (1979, p.125) and Lentin and Williams (1993, p.14); Albertia curvicornis, according to Whitney (1979, p.125). The nomenclatural type of the genus Alterbidinium remains the holotype of Alterbidinium recticorne.
Tax. sr. synonym of Alterbia curvicornis (Vozzhennikova, 1967) Lentin and Williams, 1976, according to Whitney, 1979.
Holotype: Wilson, 1967, fig.12
Locus typicus: Campbell Island, New Zealand
Stratum typicum: ?Teurian, Palaeocene
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Original description as Deflandrea acutula: [Wilson, 1967, p. 225-226]:
Description:
Test narrow, bi-layered, comprising smooth outer cyst tapering at poles, and smaller inner cyst. Right antapical horn long (l=14-36 µm), pointed. Left antapical horn absent, but position represented by minor angularity in margin of outer cyst.
Archaeopyle long, narrow, intercalary, situated on dorsal epitheca; operculum hinged to shell by posterior margin.
Spiral transverse girdle represented by a folding of outer cyst.
Dimensions:
Holotype: l=83 µm, b=44 µm, inner cyst 44x36 µm.
Two other measured specimens: SM 621: l=116 µm, b=47 µm, inner cyst 47x39 µm; SM 602: l=94 µm, b=50 µm, inner cyst=44x41 µm.
Affinities:
D. acutula shares certain features with several Antarctic species of Deflandrea described recently by the author (Wilson, 1967). In particular the archaeopyle resembles that of D. asymmetrica and D. distincta, although it is much narrower. All three species possess a flat-tipped apical horn. D. acutula is distinguished from the two Antarctic species by its different shell outline, greater development of the right antapical horn, and the absence of a left antapical horn.
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Emended description as Alterbidinium acutulum:
Khowaja et al., 1991. p. 42-44:
Diagnosis:
Cyst proximate, dorsoventrally compressed, circumcavate; pericyst ambitus pentagonal with an apical and two symmetrically placed unequal antapical horns, right antapical horn reduced; periphragm thin, smooth, endocyst subpentagonal, endophragm thicker than periphragm, smooth, periparacingulum present, annulate; paratabulation indicated by archaeopyle and periparacingulum only; archaeopyle intercalary, independently developed on periphragm and endophragm; periarchaeopyle hexa 2a, isodeltaform, perioperculum adnate; endoarchaeopyle hexa 2a, eury-deltaform, endoperculum adnate.
Description:
Shape: Cyst proximate, dorso-ventrally compressed; pericyst ambitus pentagonal with a broad based apical horn and two symmetrically placed unequal antapical horns, right antapical horn reduced; endocyst subpentagonal.
Wall relationship: Apical and antapical pericoels connected through ambital pericoel (circumcavate); endocyst shifted more towards dorsal side where the periphragm and endophragm are appressed in precingular and postcingular areas.
Wall features: No parasutural features; periphragm and endophragm thin but endophragm thicker than periphragm; periparacingulum, annulate running high over endocyst, marked by two parallel ridges and a furrow in between; periparasulcus marked by a depression.
Paratabulation: Indicated by archaeopyle and periparacingulum only.
Archaeopyle: Intercalary, independently developed on periphragm and endophragm; periarchaeopyle hexa 2a, iso-deltaform, perioperculum adnate (adnation along adcingular margin); endoarchaeopyle hexa 2a, eury-deltaform, endoperculum adnate (adnation along adcingular margin ).