A new <i>Paramoeba</i> Isolate from Florida Exhibits a Microtubule-Bound Endosymbiont Closely Associated with the Host Nucleus

The genera <i>Paramoeba</i> and <i>Neoparamoeba</i> , within the family Paramoebidae (order Dactylopodida), are distinguished by their dactylopodial pseudopodia and the presence of an intracellular eukaryotic symbiont, the <i>Perkinsela</i> -like organism (PLO). Taxonomic classification within these genera has been challenging due to overlapping morphological traits and close phylogenetic relationships. Most species are marine, with some acting as significant parasites, contributing to sea urchin mass mortality and serving as causative agents of Amoebic Gill Disease (AGD). Despite their ecological and economic importance, many aspects of their diversity, biology, evolution, and host interactions remain poorly understood. In this study, we describe a novel amoeba species, <i>Paramoeba daytoni</i> n. sp., isolated from Daytona Beach, Florida. Morphological and molecular analyses confirm its placement within the <i>Paramoeba</i> clade, closely related to <i>P. eilhardi, P. karteshi,</i> and <i>P. aparasomata</i> . Phylogenetic assessments using 18S and COI markers demonstrate the limitations of 18S gene for species delineation, highlighting COI as a more reliable genetic marker for this group. Additionally, observations on PLO morphology, movement, and microtubule association provide insights into the endosymbiotic relationship, reinforcing the need for further research into this unique eukaryote-eukaryote symbiosis.