Note
Glass sponges (Hexactinellida) are a group of deep-water benthic animals that have a unique syncytial organization and possess a characteristic siliceous skeleton. Although hexactinellids are traditionally grouped with calcareous and demosponges in the phylum Porifera, the monophyly of sponges and the phylogenetic position of the Hexactinellida remain contentious. We determined and analyzed the nearly complete mitochondrial genome sequences of the hexactinellid sponges Iphiteon panicea and Sympagella nux.