Vilesida, a new order of demosponges revealed by molecular phylogeny and abundant 24-isopropylcholesterols (24-ipc sterols)

Abstract We propose the creation of Vilesida ord. nov. (Porifera: Demospongiae), initially discovered thanks to molecular markers. Species from this new order share monactinal and diactinal megascleres arranged in a confused halichondrioid fashion and are currently scattered in the orders Suberitida, Bubarida, and Axinellida. All species analysed share a chemical synapomorphy not found in any other eukaryotic group: C30 sterols with an isopropyl group in the sidechain at C-24 as their major membrane sterols. These are precursors of the sterane 24-isopropylcholestane, abundant in some Neoproterozoic oils/rocks and hypothesized to be an early sponge biomarker. We propose: (i) the resurrection of Viles; (ii) its establishment as the type genus of Vilesidae fam. nov., the only family present in the new order; (iii) the reallocation of Petromica and Axinyssa to the new order; and (iv) the creation of Murus gen. nov. in Vilesidae fam. nov. The type species of Murus, Murus hirondellei comb. nov., was previously placed in Phakellia (order Bubarida). In addition, we describe two new species from the Northeast Atlantic and the Mediterranean: Murus profunda sp. nov. and Murus sinenotis sp. nov.