An appraisal of the problems related to species identity and species diversity within chelonian polystomes (Polystomatidae: Monogenea)
The subfamily Polystomoidinae Yamaguti, 1963, belongs to the class Monogenea that are parasites of terrapins and of the caecilian polystome Nanopolystoma Du Preez et al., 2008. Chelonian polystomes include three genera: Neopolystoma Price, 1939, whose members have no hamuli, or large hooks, Polystomoidella Price, 1939, whose members possess one pair of hamuli, and finally Polystomoides Ward, 1917, whose members possess two pairs of hamuli. Chelonian polystomes comprise of a total of 59 species collectively, with Neopolystoma having 21, Polystomoidella three, and Polystomoides 35 species respectively. Together with these species names, it is unfortunately true that a great many synonyms also exist. This is as a result of the polystomes of chelonians that have been poorly studied, and/or a large number of the species that have been described in obscure journals. To further complicate matters, terrapin classification is not stable and various changes have occurred over the past few decades. This taxonomic complexity is further exacerbated by the fact that no definite protocol exists for one to follow in the event of describing new species, and very important measurements and characteristics are often omitted. The aims of this study are, firstly, to provide a systematic summary of the existing chelonian polystome species in order to simplify the clutter of information that currently exists and also to facilitate the identification of new species by presenting the data in the form of a simple reference system. Secondly, the paucity of morphometric polystome marginal hooklet measurements is addressed, and a protocol is developed and proposed for a simplified measurement strategy to facilitate distinguishing between chelonian polystomes. Finally, two new eye polystome species from two Florida terrapin hosts collected in 2004 are reported and described.