New species and a molecular dating analysis of Vetulina Schmidt, 1879 (Porifera: Demospongiae: Sphaerocladina) reveal an ancient relict fauna with Tethys origin

Abstract

Vetulina Schmidt, 1879 (Demospongiae, Sphaerocladina, Vetulinidae) currently constitutes the only living representative of a once diverse Mesozoic group. Molecular data place Vetulina as a sister taxon to freshwater sponges (Spongillida) despite different skeletal composition. To date, only three extant species of this desma-bearing 'rock sponge' have been described from the Caribbean and Indian Ocean, all with similar growth forms and spiculation, but different desma and surface details. Comparison of these genetically very similar species was not possible until the present study. The distribution of Vetulina is taken to be a consequence of the closure of the Tethyan Seaway in the Early Miocene, suggesting a more widely distributed population with its origin in the Tethys Sea. To support this hypothesis in a molecular palaeobiological framework, we first increased the taxon sampling by describing and sequencing two new species of Vetulina from the Bahamas and Philippines and report Vetulina stalactites from nine additional locations in the Tropical Western Atlantic. A robust, dated phylogeny was calculated from the combined dataset and amended by five representative fossils. Our results point to an Eocene origin for Vetulina, even before the closure of the Tethyan Seaway in the Miocene, supporting the hypothesis that Vetulina presents a relict fauna with its origin in the Tethys Sea.