Bullinularia minor Hoogenraad & De Groot, 1948

Diagnosis: Habitus, shape, colour, and structure of the test show in general a strong resemblance to that of B. indica. All these features, however, often display slight aberrations, difficult to describe in words or to delineate in drawings. In oral–aboral view the test shows a very regular broad elliptical or nearly circular outline, the margin usually very smooth due to the absence of projecting xenosomes. In lateral view the form appears strongly compressed. Colour varies little: dark yellow, sometimes with a brighter or, in other cases, a darker brown tint. The wall appears rather thin; therefore, the test never shows the opaque, sometimes nearly black appearance characteristic of B. indica. In more lightly tinted individuals the cleft of the aperture shines faintly but distinctly through the fundus wall.

The test structure is dominated by chitinoid cement, especially on the oral sides. The xenosomal covering is only moderately developed, consisting mainly of scattered quartz grains and, among them, sometimes numerous organic particles—a structure quite different from the dense, blunt mosaic typical of B. indica and also from that of Trigonopyxis arcula from some localities.

The structure of the oral field is essentially the same as in B. indica. The aperture cleft, in vertical projection, appears narrowly elliptical with undulating margins; upper and lower lips are normally developed, with a thickened and darker rim caused by a denser accumulation of pseudo‑chitin. The upper lip often projects as a triangular tip. Owing to the usual transparency of the test, the structure and shape of the aperture can also be studied from the side. In this view, the aperture lies in a distinct inward bending of the test plane, and the upper and lower lips appear to be positioned at very different levels. As a consequence, the plane of the aperture often stands more or less perpendicular to the oral plane of the test, and the aperture itself appears much less cleft‑like and wider than one would expect from the usual projection view. A similar phenomenon may occur in B. indica, but seldom as distinctly as in B. minor. The pores in the upper lip—so characteristic for B. indica—are in B. minor normally developed in number, size, and arrangement.

Penard (1912) mentions unusually small variants of B. indica (130–170 µm and 120–125 µm). Jung (1934) also observed such small forms, including one of 90 (126) µm length. As shown by our measurements, B. minor is considerably smaller still. Moreover, transitional forms between this species and the B. indica specimens occurring in the same sample were entirely absent, justifying its description as an autonomous species.

After its discovery in a sample from New Zealand, we found it again in material from Greenbank (New Jersey, U.S.A.), in an almost identical form, though represented by only a single specimen.

All from Hoogenraad & De Groot, 1948.