Long-read sequencing (e.g. Nanopore's MinION or PacBio) has the potential to dramatically improve genome assembly but the quality of the reads is critically dependent upon the quality of the input gDNA. \n\nHere I describe the extraction of high molecular weight DNA from the calcareous sponge, Sycon capricorn. I choose to use Qiagen RLT buffer in the initial lysis step as this solution results in higher molecular weight DNA compared to alternatives. I suspect that RLT is deactivating endogenous DNases that would otherwise digest the gDNA.