We define terms used to describe the transition from a trochospiral, multiserial or biserial chamber arrangement to a uniserial chamber arrangement in benthic foraminifera. The morphological transition from a trocho-, multi- or biserial to a uniserial chamber arrangement may be abrupt, or form a morphological progression through transitional stages defined as ‘loosely biserial’, ‘lax-uniserial’ and, finally, ‘loosely uniserial’. The precise meanings of the intermediate stages ending in uniseriality are defined here by means of examples using foraminiferal models. We introduce the new terms ‘Cryptobiserial’, ‘Cryptotriserial’ and ‘Cryptotrochospiral’ to describe the chamber arrangement in genera with uniserial stages that preserve the sense of coiling of the previous trochospiral, triserial or biserial stages.

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