Abstract
Underground waters are still one of the most important sources of drinking water for the planet. Moreover, the fauna that inhabits these waters is still little known, even if it could be used as an effective bioindicator. Among cave invertebrates, planarians are strongly suited to be used as a study model to understand adaptations and trophic web features. Here, we show a systematic literature review that aims to investigate the studies done so far on groundwater-dwelling planarians. The research was done using Google Scholar and Web of Science databases. Using the key words “Planarian cave” and “Flatworm Cave” we found 2273 papers that our selection reduced to only 48, providing 113 usable observations on 107 different species of planarians from both groundwaters and springs. Among the most interesting results, it emerged that planarians are at the top of the food chain in two thirds of the reported caves, and in both groundwaters and springs they show a high variability of morphological adaptations to subterranean environments. This is a first attempt to review the phylogeny of the groundwater-dwelling planarias, focusing on the online literature. The paucity of information underlines that scarce attention has been dedicated to these animals. Further revisions, including old papers and books, not available online will be necessary.
Highlights
Invertebrates embrace the mainstream of metazoan diversity, but only a very small portion of invertebrate species is generally considered in environmental conservation actions [1]
Cenocnysidering the extension of karst areas worldwide and the relative frequency of flatworms’ occurrence in groundwaters, it is likely that the lack of papers that we underlined especially for the southern hemisphere reflects the few researches performed and the low attention payed to flatworms during fauna surveys in cave environments
Our results show that the occurrence of eyes in depigmented stygobiont planarians is high in springs, such as at the interface with groundwaters
Summary
Invertebrates embrace the mainstream of metazoan diversity, but only a very small portion of invertebrate species is generally considered in environmental conservation actions [1]. There is a high invertebrate diversity that mirrors the miscellaneous array of micro-habitat typologies that are available in the aquatic environments [5]. These micro-habitats have various sizes ranging from the small interstices and crevice of the streams substrate, that host unique assemblages of invertebrates enhancing the occurrence of beta diversity [6,7], to large river connections and systems, characterized by ancient drainages that allowed astounding species radiation in different invertebrate groups [8]. Despite being a fundamental source of biodiversity, several highly diverse taxa of aquatic invertebrates, like planarians, remain still poorly known and poorly considered in research and conservation projects
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