The complete mitochondrial genome of Korean endemic species, Timarete posteria (Polychaeta, Cirratulidae)

Complete mitochondrial genome and phylogenetic analysis of Cirriformia tentaculata (Annelida, Polychaeta, Cirratulidae) from Weihai, Shandong, China

Cirriformia species usually inhabit intertidal zones and deep-sea sediments. Their accurate identification has proven to be challenging. Here, we present the complete mitochondrial genome of one Cirriformia tentaculata_Montagu 1808 specimen collected from China. The total length of the complete mitochondrial sequence of C. tentaculata is 15,516 bp and consists of 13 protein-coding genes (PCGs), 23 tRNA genes, two rRNA genes, and an A + T rich region (64.20%). All PCGs begin with the typical ATN start codon, except for cox1, which uses TTG. TAA or TAG serve as termination codons for twelve PCGs, while nad5 terminates with an incomplete codon, T. The phylogenetic tree revealed a close relationship between C. tentaculata in this study, and Cirriformia cf. tentaculata and Timarete posteria from Korea. The information will assist in the future identification and understanding of this species and offers a novel point of reference for identifying Cirriformia species, and phylogenetic studies.

First mitochondrial genomes of Chrysopetalidae (Annelida) from shallow-water and deep-sea chemosynthetic environments

Among Annelida, Chrysopetalidae is an ecologically and morphologically diverse group, which includes shallow-water, deep-sea, free-living, and symbiotic species. Here, the four first mitochondrial genomes of this group are presented and described. One of the free-living shallow-water species Chrysopetalum debile (Chrysopetalinae), one of the yet undescribed free-living deep-sea species Boudemos sp., and those of the two deep-sea bivalve endosymbionts Craseoschema thyasiricola and Iheyomytilidicola lauensis (Calamyzinae). An updated phylogeny of Chrysopetalidae is performed, which supports previous phylogenetic hypotheses within Chrysopetalinae and indicates a complex ecological evolution within Calamyzinae. Additionally, analyses of natural selection pressure in the four mitochondrial genomes and additional genes from the two shallow-water species Bhawania goodei and Arichlidon gathofi were performed. Relaxed selection pressure in the mitochondrion of deep-sea and symbiotic species was found, with many sites under selection identified in the COX3 gene of deep-sea species.

Still Digging: Advances and Perspectives in the Study of the Diversity of Several Sedentarian Annelid Families

Sedentarian annelids are a diverse and heterogeneous group of marine worms representing more than 8600 species gathered in ca. 43 families. The attention brought to these organisms is unevenly distributed among these families, and the knowledge about them sometimes scarce. We review here the current knowledge about the families Acrocirridae, Cirratulidae (including Ctenodrilidae), Cossuridae, Longosomatidae, Paraonidae, and Sternaspidae in terms of biodiversity as well as the evolution of the taxonomy and systematics of each group. We present the challenges faced when studying these organisms and compare methodologies across groups and perspectives in future research.