Epizoic and Apochlorotic Tursiocola species (Bacillariophyta) from the Skin of Florida Manatees (Trichechus manatus latirostris)

Abstract

Until now only one group of diatoms, the Bacillariaceae, was known to contain heterotrophic representatives. We show that a second group, represented by species in the genus Tursiocola, has undergone evolutionary loss of photosynthesis within the Bacillariophyta. Heterotrophy was evidenced by the presence of only apochlorotic cells in live and motile specimens. Three species of Tursiocola (T. bondei sp. nov., T. alata sp. nov., and T. gracilis sp. nov.), of which at least two are apochlorotic, are described as new to science from the skin of Florida manatees. T. ziemanii and T. varicopulifera were also observed to be apochlorotic. A new morphological feature termed a "fastigium" was observed on some Tursiocola spp. and is described as an extension of the mantle margin at the valve apex that overhangs the apex and extends towards the valve face. The presence of greatly elevated marginal ridges on the valve face of T. alata sp. nov. is a newly observed morphological character within the genus. Phylogenetic analyses using ribosomal RNA sequences indicate that Tursiocola is monophyletic, though morphological character analysis suggests paraphyly as species of the closely related Epiphalaina genus are embedded within a larger Tursiocola clade.

Keywords: Character analysis; commensalism; heterotrophic diatoms; morphology; new species; phylogenetics..