- according to Hottinger (2006):
BICONCH - protoconch and deuteroconch together, if separated by a straight septum, thus differing in shape from later, curved ones. The straight septal wall suggests that hydrostatic pressure in protoconch and deuteroconch was equal as a morphogenetic control before the wall was calcified. Thus, the two first chambers were formed together and represent a single growth stage similar to an embryonic apparatus.
Remarks: The status of a biconch as a particular growth stage is supported by Röttger's (1974) observation that biconchs in nummulitids are formed after hatching, i.e. after the naked embryo is squeezed out of the narrow canal orifices. In such biconchs, the second chamber is used to keep the few symbionts transmitted from the mother shell in their first stage of procreation within the new generation of their hosts. Other embryos calcify their shell with straight septa beween the first two, three or even four chambers within the mother shell and will leave it during the hatching process by dissolving chamber walls of their mother.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
Röttger (1974), Larger Foramiifera: Reproduction and early stages of development in Heterostegina depressa, Marine Biology, Heidelberg, vol. 26, p. 5 – 12.