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Zooxanthellate octocorals of the genus Cladiella Gray, 1869 are common on Indo-Pacific coral reefs, including in the Red Sea. Among the 61 species listed in WoRMS, 27 species were originally described from the Red Sea, mostly based on material collected in the 19th century. The latter includes the type species of the genus as well as the three other oldest known species of the genus. The goals of the present study were to locate the various natural history museum depositories of the 27 Red Sea types and to redescribe the types for the first time since their initial description. All type colonies were found and re-described using whole-colony photography and scanning electron microscopy (SEM) to depict their sclerites. SEM images provide the dimensions and the detailed surface-microstructure of all sclerite types present across all type materials. These findings led us to a revised diagnosis of the genus and an updated description of all 27 types. The results present a comprehensive overview of all of the Red Sea Cladiella type colonies, constituting the first step towards a complete taxonomic revision of this speciose genus.  

Abstract DNA cytosine methylation is central to many biological processes, including regulation of gene expression, cellular differentiation, and development. This DNA modification is conserved across animals, having been found in representatives of sponges, ctenophores, cnidarians, and bilaterians, and with very few known instances of secondary loss in animals. Myxozoans are a group of microscopic, obligate endoparasitic cnidarians that have lost many genes over the course of their evolution from free-living ancestors. Here, we investigated the evolution of the key enzymes involved in DNA cytosine methylation in 29 cnidarians and found that these enzymes were lost in an ancestor of Myxosporea (the most speciose class of Myxozoa). Additionally, using whole-genome bisulfite sequencing, we confirmed that the genomes of two distant species of myxosporeans, Ceratonova shasta and Henneguya salminicola, completely lack DNA cytosine methylation. Our results add a notable and novel taxonomic group, the Myxosporea, to the very short list of animal taxa lacking DNA cytosine methylation, further illuminating the complex evolutionary history of this epigenetic regulatory mechanism.