From Fensome et al., 2019:
Alterbidinium pilosum, (Davey, 1969b, p.9, pl.3, figs.2–5) Lentin and Williams, 1985, p.15.
Holotype: Davey, 1969b, pl.3, figs.2,5.
Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly (and now) Alterbidinium.
Age: Campanian–Maastrichtian.

Locus typicus: Northern Natal, South Africa

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Original diagnosis as Deflandrea pilosa: [Davey, 1969, p. 9]:
Fusiform test having a thin outer wall which bears minute hairs and granules. Apical horn stout, blunt or rounded distally; single antapical horn asymmetrically placed, conical. Inner body large, in contact with the outer wall except in the apical and antapical regions.
Cingulum moderately well developed, almost circular, broken by a sulcus which extends to the apex.
Archaeopyle intercalary, the operculum typically remaining in position.

Original description:
The minute hairs and granules are not densely arranged and are not aligned. The hairs are often stouter along the borders of the cingulum and may here be termed spines. The operculum is usually attached to the test along its antapical margin and thus remains in position. An interesting feature is that this species is scarcely stained by safranin.

Dimensions:
Holotype: overall length 57 µm, width 46 µm, inner body 38 by 42 µm.
Range: overall length 55(58.4)61 µm, width 38(42.0)45 µm. Number of specimens measured, 10.

Affinities: (p.10)
The overall form and the nature of the ornamentation easily distinguish D. pilosa from all previously described species.