Test Fusion in Adult Foraminifera: A Review With New Observations of an Early Eocene Nummulites Specimen

Abstract

In foraminifera, so-called "double tests" usually arise due to abnormal growth originating mainly from twinning, but may also be caused by irregularities in the early chambers and by regeneration after test injury that modifies the direction of growth. A fourth cause of double tests has only rarely been reported: the fusion of the tests of two adult individuals. We studied an early Eocene Nummulites double test consisting of two adult individuals that fused after an extended period of independent growth. The specimen was studied using computed tomography with micrometric resolution (micro-CT) that allowed bi-and three-dimensional visualization of the internal structure. Before fusion each individual test had 30-36 chambers, which, by comparison with growth rates in recent nummulitids, implies at least three months of independent growth. After fusion, the compound test grew in two spirals that fused after about one whorl and then continued in a single spiral.To fuse their tests, either adult individuals have to be forced to do so or the allorecognition (ability to distinguish between self and another individual) mechanisms must fail. A possible explanation for the merged Nummulites tests in this study is forced fusion in attached individuals after surviving ingestion and digestion by a metazoan. Alternatively, environmental stress could lead to a failure of allorecognition mechanisms and/or foraminiferal motility. Once fused, subsequent growth seems to be determined mainly by the relative orientation of individual tests. In any case, the frequency in which adult fusion occurs remains unknown.

The Occurrence of Twin Embryos, Abnormal Morphologies and Test Repair in Lower Cretaceous Orbitolinidae (Larger Benthic Foraminifera): Examples From France, Somalia, Iran, Tibet, and Texas

“…The occurrence of unusual ("abnormal") test morphologies in larger benthic foraminifera may have different origins, for example, the occurrence of plurilocular embryonic apparati, recoveries after test damage (e.g., predation, mechanical fracture), or fusion ("conjoined") (e.g., Hageman & Kaesler, 2002;Culver & Lipps, 2002;Ferràndez-Cañadell et al, 2014;Briguglio et al, 2016). Extreme environmental conditions (e.g.…”

“…Briguglio et al (2016) reported the occurrence of at least 16 embryos in one adult specimen of modern Cycloclypeus Carpenter. For further details about the causes and mechanisms of twin embryo development see Ferràndez-Cañadell et al (2014) and Benedetti (2015). Pluriembryonal embryonic apparati have been observed in Paleozoic fusulinids (Wilde, 1965), mid-Cretaceous alveolinids (Hottinger, 1974;Özgen-Erdem et al, 2003;Mathieu et al, 2011), Upper Cretaceous-Paleogene orbitoidal larger foraminifera (orbitoidids, orthophragminids, lepidocyclinids) (Meriç, 1964(Meriç, , 1970(Meriç, , 1971(Meriç, , 19731992;Omana et al, 2012;Bene-detti, 2015), and recent taxa such as Cycloclypeus (Briguglio et al, 2016).…”

Imaging the internal structure of Borelis schlumbergeri Reichel (1937): Advances by high-resolution hard X-ray microtomography

“…Hard X-ray microtomography (µCT) has experienced enormous progress in efficient 3D imaging with micrometer resolution and has been increasingly recognized as an indispensable tool by paleontologists (Cunningham et al, 2014;Hoffmann et al, 2014). Owing to the true micrometer resolution, the non-destructive technique is increasingly applied in micropaleontology, paleoceanography and other fields of earth sciences (Speijer et al, 2008;Abel et al, 2012;Görog et al, 2012;Masschaele et al, 2007;Briguglio et al, 2011;chapter 6 in Branson, 2014;Briguglio et al, 2013;Ferràndez-Cañadell et al, 2014;Briguglio et al, 2016;Schmidt et al, 2013;Johnstone and Barker, 2010;Cnudde and Boone, 2013).…”

Innovative TEM-coupled approaches to study foraminiferal cells

“…One solution to the foraminiferal size issue is micro-X-ray computed tomography (CT), which also provides information on internal structures. Micro-X-ray CT has been used to assess attributes regarding foraminiferal tests (shells), such as biometry (Speijer et al 2008;Briguglio et al 2011Briguglio et al , 2013Hohenegger and Briguglio 2012;Ferrández Cañadell et al 2014) and test-wall dissolution by means of X-ray attenuation (Johnstone et al 2010;Iwasaki et al 2015). Nomaki et al (2015) applied X-ray CT to foraminiferal cells prepared for TEM (i.e., resin embedded; stained with heavy metals).…”