The “index of the copulatory apparatus” and its application to the systematics of freshwater pulmonates (Mollusca: Gastropoda: Pulmonata)

M.V. Vinarski

Abstract. The index of the copulatory apparatus (ICA) is calculated as the ratio between lengths of the praeputium and the penis sheath in the copulatory apparatus in freshwater pulmonate mollusks. ICA is often used for species’ delimitation and identification in different taxa of pulmonates, however, its variation (in both intra- and interspecific levels) is still poorly studied that may make troubles for systematicists. The variation of ICA in pond snails (family Lymnaeidae Rafinesque, 1815) has been studied in several aspects (intra- and interpopulation, interspecific). It has been shown that the index varies considerably, and it is almost impossible to identify a single specimen on the base of ICA solely. However, mean ICA values are more useful for taxonomic and identification purposes. Closely related species of lymnaeids demonstrate some extent of overlap between their ranges of ICA variation that hampers their identification but is not a cause for synonymisation. The factors of different origin that potentially may influence the ICA values in freshwater pulmonates have been reviewed. It is revealed that ICA manifests significant ontogenic and (in some lymnaeid species) geographical changes. The use of ICA in pulmonate systematics should be accompanied by data on variation in another characters of conchological or anatomical kind.

Key words: pulmonates, taxonomy, species delineation, species identification, variation, copulatory apparatus, Lymnaeidae

Zoosystematica Rossica, 2011, 20(1): 11-27 ▪ Published in print 28 July 2011

https://doi.org/10.31610/zsr/2011.20.1.11 ▪ Open full article

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