Heterogeneity among juvenile megalospheres in Peneroplis pertusus (Forskål) from the Line Islands (Pacific Ocean): Size range, morphotypes, and test deformations

Sixty fully calcified megalospheric juveniles were recovered from the brood chambers of an adult specimen of the symbiont-bearing foraminifer Peneroplis pertusus (Forskål) collected at Kiritimati Atoll (Line Islands, Pacific Ocean). All juvenile megalospheres consist of a proloculus and an elongated flexostyle that is one half coil in length except for one specimen consisting of only the proloculus. The juvenile specimens exhibit distinct variations in size, various forms of test deformation, and can be classified into four distinct morphotypes. The juvenile test deformations show that the calcification of the megalospheres in the brood chambers is not simultaneous but asynchronous and a key mechanism driving the test deformation in juvenile megalospheres of Peneroplis. Observations on more than 100 adult specimens show that the test deformities observed in juvenile specimens are not expressed in adult forms, indicating that they are either transitioning to normal growth forms or are not viable.