engleski

Morphological variations in sea turtle-associated “gomphonemoid” diatoms

Very recently, several new diatom taxa have been described living epizoically on sea turtles. Among them, two new genera, Poulinea Majewska & al. and Chelonicola Majewska & al. (Majewska & al. 2015), described from nesting olive ridleys in Costa Rica, were later observed in multiple samples collected from other sea turtle species from different geographic locations across the globe. Both genera possess cuneate, heteropolar frustules, morphologically (though not necessarily genetically) resembling other gomphonemoid diatom taxa, most notably Tripterion R. W. Holmes & al. (Holmes & al. 1993), a genus described from the skin of Dall’s porpoises and later found growing on other marine mammals (whales) but also on abiotic substrates (Fernandes & Sar 2009). Several inconsistencies in the current description of Tripterion have been highlighted (Fernandes & Sar, 2009, Frankovich & al. 2016) and Riaux-Gobin & al. (2017) further questioned the description of Poulinea, indicating incorrect character coding used in the cladistic analysis applied by Majewska & al. (2015) to differentiate Poulinea from Tripterion. Although Riaux-Gobin & al. (2017) noted that the small sea turtle- associated diatoms they examined showed a relatively simple morphology and a certain level of morphological variability, another two, morphologically very similar, taxa were described as Chelonicola caribeana Riaux-Gob. & al. and Tripterion societate ‘societatis’ Riaux-Gob. & al., the latter being almost indistinguishable from the previously described Poulinea lepidochelicola Majewska & al. The current study characterizes over 20 populations of epizoic “gomphonemoid” diatoms found on five sea turtle species inhabiting all three oceans, highlighting both the remarkable morphological plasticity found within each of these populations and the lack of morphological discontinuity among them. As diatom epibiosis on sea turtles (and other marine and freshwater animals) attracts growing attention, further new forms are expected to be discovered in on- going surveys, and it must emphasized that, especially in the case of these small-celled heteropolar specimens, new taxa should be described with extreme caution.

diatoms ; taxonomy ; morphology ; sea turtles

nije evidentirano