Abstract
Invertebrates are a source of previously unknown RNA viruses that fill gaps in the viral phylogenetic tree. Although limited information is currently available on RNA viral diversity in the marine sponge, a primordial multicellular animal that belongs to the phylum Porifera, the marine sponge is one of the well-studied holobiont systems. In the present study, we elucidated the putative complete genome sequences of five novel RNA viruses from Hymeniacidon sponge using a combination of double-stranded RNA sequencing, called fragmented and primer ligated dsRNA sequencing, and a conventional transcriptome method targeting single-stranded RNA. We identified highly diverged RNA-dependent RNA polymerase sequences, including a potential novel RNA viral lineage, in the sponge and three viruses presumed to infect sponge cells.