Species Diversity and Mitochondrial DNA Analysis of Sponges (Porifera, Demospongiae) in an Anchialine Cave on the Yucatan Peninsula

The anchialine ecosystem in the southeastern Gulf of Mexico has an unexplored fauna, among the most understudied groups is Porifera, molecular approaches to investigate their biology and evolution remain largely short. To broaden these studies, sponge individuals collected in the anchialine cave Xcalac in the Mexican state of Quintana-Roo were analyzed using 18S rRNA sequences from sponge metagenomes. The three individuals studied belong to the Cinachyrella, Xestospongia, and Suberites genera. The mitochondrial (mt) genomes of Cinachyrella sp. n. and Xestospongia sp. n. were 18,493 bp to 19,604 bp in length, containing 14 protein-coding genes, 2 rRNA genes (rrnS and rrnL), and 23~25 tRNA genes, respectively. The phylogenomic analysis showed that Cinachyrella sp. n. had the same gene arrangement as the members of its subclade, including sponge species of the Cinachyrella and Geodia genera. The mt genome of Xestospongia sp. n. contained the same gene arrangement as found in other sponges of the same genus and differed from other genera such as Petrosia and Haliclona by an tRNA (tyrosine, Y1). Variation in mitochondrial genomes (size, gene content, and gene order) was observed when comparing sampled sponge species from the class Demospongiae to the class Homoscleromorpha. This is the first record of Cinachyrella sp. n and Suberites sp. n. in an anchialine cave on the southeastern Yucatan peninsula, and the first report of the mitochondrial genome analysis of Cinachyrella sp. n. and Xestospongia sp. n., contributing to a better understanding of the diversity and phylogeny of sponges in this ecosystem.