- according to Hottinger (2006):
DIMORPHISM - coexistence of two discrete morphotypes representing different generations in the life cycle of a single species. They are expressed in the adult growth stages and/or in the protoconch and in the following nepionic chambers. The protoconch diameter is large (megalospheric = A - form) when the agamont's protoplasm is distributed (including eventual symbionts) among the cloned offspring. The protoconch diameter is small (microspheric = B - form) when the gamont's gametes fuse pairwise to form a zygote whith no protoplasm or symbionts from the mother. If there is dimorphism in the adult shell, the B - form becomes larger than the A - form. The compartments of the microspheric initial phases are small. It takes many growth steps to reach the initial shell size of the megalospheric generation. Reaching the adult oversize of the microspheric generation demands numerous additional instars. Consequently, the dimorphism of foraminiferal generations reflects different life times and thus different strategies of life within the same species: the microspheric generation is adapted to the permanent basic low-level carrying capacity of an oligotrophic and warm environment, while the megalospheric generation with its short life time adapts to both spring and eventual autumn seasonal peaks of carrying capacity. Nepionts with large megalospheres may have a particular architecture different from that of the adult (see megalospheric apparatus). In complex life cycles, a third (schizontic) generation may produce megalospheric shells with a morphology slightly different from that of the gamonts.
- A - form
- B - form
- life cycle
- odd pairs
Goldstein (1999), Foraminifera, a biological overview. In: SEN GUPTA B.K. (ed.), Modern Foraminifera, Kluwer Academic Publishers, Dortrecht, p. 37-55.
Hottinger (1977), Foraminifères operculiniformes, Mémoires du Muséum National d'Histoire Naturelle, Paris, (Série C, Sciences de la terre), t. XL, 159 p. + 66 pls.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
Reichel (1933), Sur une alvéoline cénomanienne du Bassin du Beausset, Eclogae geologicae Helvetiae, Basel, vol. 26, N° 2, p. 269-280.