Mitochondrial introns intermit coding regions of genes and feature characteristic secondary structures and splicing mechanisms. In metazoans, mitochondrial introns have only been detected in sponges, cnidarians, placozoans and one annelid species. Within demosponges, group I and group II introns are present in six families. Based on different insertion sites within the cox1 gene and secondary structures, four types of group I and two types of group II introns are known, which can harbor up to three encoding homing endonuclease genes (HEG) of the LAGLIDADG family (group I) and/or reverse transcriptase (group II). However, only little is known about sponge intron mobility, transmission, and origin due to the lack of a comprehensive dataset. We analyzed the largest dataset on sponge mitochondrial group I introns to date: 95 specimens, from 11 different sponge genera which provided novel insights into the evolution of group I introns. For the first time group I introns were detected in four genera of the sponge family Scleritodermidae (Scleritoderma, Microscleroderma, Aciculites, Setidium). We demonstrated that group I introns in sponges aggregate in the most conserved regions of cox1. We showed that co-occurrence of two introns in cox1 is unique among metazoans, but not uncommon in sponges. However, this combination always associates an active intron with a degenerating one. Earlier hypotheses of HGT were confirmed and for the first time VGT and secondary losses of introns conclusively demonstrated. This study validates the subclass Spirophorina (Tetractinellida) as an intron hotspot in sponges. Our analyses confirm that most sponge group I introns probably originated from fungi. DNA barcoding is discussed and the application of alternative primers suggested.

Most lithistids occur worldwide in deep-water environments, but can be found in some places in shallow water. They are not well known in the tropical western Atlantic, despite the fact that they were first described in the late 1800s. We report here two species of poorly known theonellid demosponges (Astrophorina),Discodermia dissolutaandTheonella atlantica, and one new species,Theonella wrightae, from the north-west, south-west and south Florida shelf. There is considerable variability in habitus, colour and spiculation in this species. If samples are taken randomly from different specimens and from functionally and structurally different locations on the sponge, the specimens could be mistakenly identified or individuals of the same species could be described as different species. This report increases the number of lithistid sponges reported from the tropical western Atlantic region to 30 species, but our unpublished data suggest a much higher number of species present in this region. It is also the second report of the relatively deep-water (81 m) occurrence ofD. dissolutathat is mostly known from depths as shallow as 10–30 m.

Approximately 80% of all described extant sponge species belong to the class Demospongiae. Yet, despite their diversity and importance, accurate divergence times are still unknown for most demosponge clades. The estimation of demosponge divergence time is key to answering fundamental questions on the origin of Demospongiae, their diversification and historical biogeography. Molecular sequence data alone is not informative on an absolute time scale, and therefore needs to be “calibrated” with additional data such as fossils. Here, we calibrate the molecular data with the fossilized birth-death model, which compared to strict node dating, allows for the inclusion of young and old fossils in the analysis of divergence time. We use desma-bearing sponges, a diverse group of demosponges that form rigid skeletons and have a rich and continuous fossil record dating back to the Cambrian (~500 Ma), to date the demosponge radiation and constrain the timing of key evolutionary events, like the transition from marine to freshwater habitats. To infer a dated phylogeny of Demospongiae we assembled the mitochondrial genomes of six desma-bearing demosponges from reduced-representation genomic libraries. The total dataset included 33 complete demosponge mitochondrial genomes and 30 fossils. Our study supports a Neoproterozoic origin of Demospongiae. Novel age estimates for the split of freshwater and marine sponges dating back to the Carboniferous and the previously assumed recent (~18 Ma) diversification of freshwater sponges is supported. Moreover, we provide detailed age estimates for a possible diversification of Tetractinellidae (~315 Ma), the Astrophorina (~240 Ma), the Spirophorina (~120 Ma) and the family Corallistidae (~188 Ma) all of which are considered as key groups for dating the Demospongiae due to their extraordinary rich and continuous fossil history. This study provides novel insights into the evolution of Demospongiae. Observed discrepancies of our dated phylogeny with their putative first fossil appearance dates are discussed for selected sponge groups. For instance, a Carboniferous origin of the order Tetractinellida seems to be too late, compared to their first appearance in the fossil record in the Middle Cambrian. This would imply that Paleozoic spicule forms are not homologous to post-Paleozoic forms.

Sponges (Phylum Porifera) are among the oldest Metazoa and considered critical to understanding animal evolution and development. They are also the most prolific source of marine-derived chemicals with pharmaceutical relevance. Cell lines are important tools for research in many disciplines, and have been established for many organisms, including freshwater and terrestrial invertebrates. Despite many efforts over multiple decades, there are still no cell lines for marine invertebrates. In this study, we report a breakthrough: we demonstrate that an amino acid-optimized nutrient medium stimulates rapid cell division in 9 sponge species. The fastest dividing cells doubled in less than 1 hour. Cultures of 3 species were subcultured from 3 to 5 times, with an average of 5.99 population doublings after subculturing, and a lifespan from 21 to 35 days. Our results form the basis for developing marine invertebrate cell models to better understand early animal evolution, determine the role of secondary metabolites, and predict the impact of climate change to coral reef community ecology. Furthermore, sponge cell lines can be used to scale-up production of sponge-derived chemicals for clinical trials and develop new drugs to combat cancer and other diseases.