Hidden shelter-like associations of minute Alboglossiphonia leeches (Hirudinea: Glossiphoniidae) with sedentary animals and molluscs

Freshwater leeches are a diverse group of annelid worms, some of which may serve as endosymbionts of various freshwater invertebrates, being commensals and parasites. However, the nature of such hidden associations is poorly understood. Here, we describe the first record of a freshwater leech – sponge association ever discovered. A small fragment of an unidentified and probably new freshwater sponge species (Porifera: Spongillidae) from India was heavily infested by numerous juvenile leeches Alboglossiphonia pahariensis Nesemann & Sharma, 2007 (Hirudinea: Glossiphoniidae), which were found in chironomid larvae (Diptera: Chironomidae: Xenochironomus sp.) burrows, penetrating the sponge’s body. The taxonomic identification of the leech was confirmed by means of an integrative approach combining morphological and DNA-based evidence. Furthermore, we present a finding of Alboglossiphonia bhamoensis sp. nov. from the mantle cavity of a freshwater mussel species in Myanmar. These new records are discussed within a broader ecological and evolutionary context based on a review of the body of available literature on hidden shelter-like and parasitic associations of leeches with gastropods, bivalves, and sedentary animals in freshwater environments.