Morphological and molecular analysis of Ephydatia fluviatilis (Porifera: Spongillida: Spongillidae) from Nanjing, China

Abstract

We present a comprehensive morphological description of Ephydatia fluviatilis collected in Nanjing for the first time in studies of freshwater sponges in China, based on scanning electron micrography of the sponge meshwork, the megascleres, the gemmules, and the delicate gemmuloscleres, in comparison with relevant data reported worldwide. The morphotype revealed in this study shows a peculiar spicular complement of the skeleton composed of two types of megascleres (the normal oxeas and occasional styles) with abundant tiny, centrally distributed microspinoses, gemmules (ca. 440 μm in diameter) bearing two types of spinose decoration on the shaft (i.e., erect long spines and microspinoses). We report the first complete ITS sequences of the morphotype of E. fluviatilis from China, which, combined with homologous sequences of related taxa from GenBank, are used in a phylogenetic analysis in order to understand the species relationship within Ephydatia and neighbouring taxa. Combining the ITS phylogeny and the gemmulosclere morphotypes, we identify three clades in the paraphyletic genus Ephydatia that are distinguished by different birotule gemmulosclere morphotypes for gemmule-bearing species. Multiple losses of gemmules within endemic taxa, as previously proposed, are confirmed in this study in a phylogenetic context obtained herein. Additionally, genetic similarities are found in some morphologically diverse species, likely indicating recent endemism leading to morphological specialization. Considering the diverse fossil record of Ephydatia from Cenozoic sedimentary strata of wide geographic ranges, we hypothesize that Ephydatia might have a deep root in the Paleogene or earlier and experienced a rapid, Quaternary radiation with emergences of specialized endemic species that lost gemmules under glacial-interglacial paleoenvironment.