"Tretomphaloid" float chambers in the Discorbidae and Cymbaloporidae

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Abstract
The planktonic stage of life adopted by the gamonts of some species of the Discorbidae and Cybaloporidae has led to the independent evolution of modified tests with flotation structures which are functionally analogous but morphogenically distinct. In the Discorbidae some tropical species derived from Rosalina and, separately, from Neoconorbina develop subhemispherical imperforate float chambers each with a single central tube: that of R. (Tretomphalus) is short and inwardly projecting; that of N. (TRETOMPHALOIDES ), subgen. nov., is continuous from the umbilicus of the spiral test to the areal apertures of the enclosing balloon chamber. In the Cymbaloporidae, species of Cymbaloporetta s.s. have a peripherally lobed imperforate float chamber, which may develop multiple peripheral internal tubes. C. (MILLETTIANA ), subgen. nov., uniquely possesses ramifying peripheral tubes formed by fusion of the float chamber to the enclosing, imperforate balloon chamber. A neotype for R. (T.) bulloides is proposed in order to clarify and stabilize the nomenclature.