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Polystomes (Monogenea: Polystomatidae) of freshwater turtles are currently represented by five genera, namely Neopolystoma, Polystomoides, Polystomoidella, Uropolystomoides and Uteropolystomoides. These parasites can infect the urinary, oral and/or the conjunctival sac systems of their hosts, showing strict site specificity. A recent phylogenetic study showed that the two most diverse genera within chelonian polystomes, i.e. Neopolystoma and Polystomoides, are not monophyletic. Furthermore, polystomes infecting the conjunctival sacs of their host, except for one species, formed a robust lineage. A fusiform egg shape has been reported for conjunctival sac polystomes and it was assumed that this characteristic could be a good character for the systematics of polystomes. Our objective in the present work was, therefore, to study more in depth the morphology of polystomes collected from the conjunctival sacs of chelonians to find characters defining a putative new genus. To achieve this objective, more specimens were collected in 2018 and 2019 from turtles sampled in North Carolina and Florida (USA) to extend taxon sampling for the phylogenetic analysis. Morphological characters of relevant polystome specimens were re-examined from several collections from Asia, Australia, Europe, South Africa, South America and North America. Based on a Bayesian tree inferred from the analysis of four concatenated genes, namely 12S, 18S, 28S and COI, polystomes found in the conjunctival sacs were grouped in three distinct lineages, the first one including a single species infecting an Australian pleurodire turtle; the second one including eleven species infecting cryptodire turtles of South America, North America and Asia; and the last one including a single species infecting a softshell cryptodire turtle of North America. Based on observations of live specimens by Dr. Sylvie Pichelin and our morphological analysis, the conjunctival sac polystomes from Australian turtles are small, can

Polystomes (Monogenea: Polystomatidae) of freshwater turtles are currently represented by five genera, namely Neopolystoma, Polystomoides, Polystomoidella, Uropolystomoides and Uteropolystomoides. These parasites can infect the urinary, oral and/or the conjunctival sac systems of their hosts, showing strict site specificity. A recent phylogenetic study showed that the two most diverse genera within chelonian polystomes, i.e. Neopolystoma and Polystomoides, are not monophyletic. Furthermore, polystomes infecting the conjunctival sacs of their host, except for one species, formed a robust lineage. A fusiform egg shape has been reported for conjunctival sac polystomes and it was assumed that this characteristic could be a good character for the systematics of polystomes. Our objective in the present work was, therefore, to study more in depth the morphology of polystomes collected from the conjunctival sacs of chelonians to find characters defining a putative new genus. To achieve this objective, more specimens were collected in 2018 and 2019 from turtles sampled in North Carolina and Florida (USA) to extend taxon sampling for the phylogenetic analysis. Morphological characters of relevant polystome specimens were re-examined from several collections from Asia, Australia, Europe, South Africa, South America and North America. Based on a Bayesian tree inferred from the analysis of four concatenated genes, namely 12S, 18S, 28S and COI, polystomes found in the conjunctival sacs were grouped in three distinct lineages, the first one including a single species infecting an Australian pleurodire turtle; the second one including eleven species infecting cryptodire turtles of South America, North America and Asia; and the last one including a single species infecting a softshell cryptodire turtle of North America. Based on observations of live specimens by Dr. Sylvie Pichelin and our morphological analysis, the conjunctival sac polystomes from Australian turtles are small, can