Tretomphalus Möbius 1880

At first glance Tretomphalus might be mistaken for a chamber of a planktonic foraminiferan, such as is shown at left, but these do not have the flat-chambered spiral shown above left.

Roughly spherical foraminiferan with coarse perforations on the ventral surface (above right). The dorsal surface is composed of a brownish spiral of increasing sized flat chambers; the whole specimen appears to be a benthic foraminiferan with an inflated chamber (similar to those in planktonic species) on the ventral side. Our specimens have been examined by an expert (S. Richardson) and appear similar to the dispersal form of the genus Tretomphalus, a shallow-water benthic group. Most, though not all, are empty shells.

Size under dissecting microscope: ~250-300µm in diameter

Tretomphalus es un género de foraminífero bentónico de la familia Rosalinidae, de la superfamilia Discorboidea, del suborden Rotaliina​ y del orden Rotaliida.​ Su especie tipo es Rosalina bulloides. Su rango cronoestratigráfico abarca desde el Mioceno hasta la actualidad.

Early stage as in Rosalina but with benthic microspheric and megalospheric generations alternating with a planktonic megalospheric generation that adds a large and complex globular double-walled float chamber over the resorbed chamber walls of the umbilical side just prior to gamogony, inner float chamber imperforate and fused to the imperforate margins of the spiralling chambers, a short narrow internal tube opening inward into the float chamber and at the opposite end leads into the space beneath the outer balloon chamber, wall of outer balloon-chamber perforate, with numerous rounded and rimmed openings scattered in the polar region above the tubular opening of the float chamber; equally biflagellate gametes are produced in the space between the float and balloon chambers and released through the pores of the terminal face, as the pseudopodia of the pelagic parents maintain their tests in contact. Miocene to Holocene; tropical to temperate waters. (Loeblich & Tappan, 1987, Foraminiferal Genera and Their Classification)