Phylogenomics-guided revision of the genus Rhytisma Alderslade, 2000 (Octocorallia: Malacalcyonacea: Lemnaliidae), with descriptions of six new species

The genus Rhytisma Alderslade, 2000 (Octocorallia: Malacalcyonacea: Lemnaliidae), formerly comprising four nominal species (R. fulvum, R. fuscum, R. monticulum and R. rubiginosum), is revised using an integrative approach. We combine morphological and phylogenomic data for newly collected and historical specimens. A neotype is designated for R. fulvum and a lectotype for R. fuscum to stabilise the application of these names. Six new species are described from the Indo-Pacific: R. acoronatum sp. nov., R. calyaceum sp. nov., R. oblongum sp. nov., R. inaequale sp. nov., R. karibu sp. nov. and R. sperkolae sp. nov. Species delimitation is supported by discrete combinations of morphological characters – particularly those of the tentacle and polyp sclerites – as well as multi-locus DNA barcoding and phylogenomic analyses of conserved elements (UCE and exon loci). Our findings highlight the diagnostic value of tentacle sclerites and reveal extensive species-level diversity that was previously obscured by insufficient morphological examination. The revised genus currently comprises 10 valid species, many of which display restricted geographic distributions, reflecting patterns of regional endemism in Indo-Pacific octocoral assemblages. These results underscore the importance of integrative taxonomy in uncovering hidden biodiversity.

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