The complete mitochondrial genome of the Ctenophore Beroe cucumis, a mitochondrial genome showing rapid evolutionary rates

Brief History of Ctenophora

Ctenophores are the descendants of the earliest surviving lineage of ancestral metazoans, predating the branch leading to sponges (Ctenophore-first phylogeny). Emerging genomic, ultrastructural, cellular, and systemic data indicate that virtually every aspect of ctenophore biology as well as ctenophore development are remarkably different from what is described in representatives of other 32 animal phyla. The outcome of this reconstruction is that most system-level components associated with the ctenophore organization result from convergent evolution. In other words, the ctenophore lineage independently evolved as high animal complexities with the astonishing diversity of cell types and structures as bilaterians and cnidarians. Specifically, neurons, synapses, muscles, mesoderm, through gut, sensory, and integrative systems evolved independently in Ctenophora. Rapid parallel evolution of complex traits is associated with a broad spectrum of unique ctenophore-specific molecular innovations, including alternative toolkits for making an animal. However, the systematic studies of ctenophores are in their infancy, and deciphering their remarkable morphological and functional diversity is one of the hot topics in biological research, with many anticipated surprises.

The enigmatic Placozoa part 2: Exploring evolutionary controversies and promising questions on earth and in space

The placozoan Trichoplax adhaerens has been bridging gaps between research disciplines like no other animal. As outlined in part 1, placozoans have been subject of hot evolutionary debates and placozoans have challenged some fundamental evolutionary concepts. Here in part 2 we discuss the exceptional genetics of the phylum Placozoa and point out some challenging model system applications for the best known species, Trichoplax adhaerens.

Revision of Beroidae (Ctenophora) in the southern seas of Europe: systematics and distribution based on genetics and morphology

Genetic and morphological analyses were used to revise historical controversies in identities of Beroe species in the southern seas of Europe. DNA analyses with ITS sequences were used to explore their phylogenetic relationships. Three species of Beroe were initially listed as occurring in the Mediterranean Sea. Recently, the specimens were often re-identified using genetic analyses, causing confusions of identity. In 1997, a non-native Beroe was introduced into the Black Sea, which established there and spread to the adjacent seas, adding more controversy and confusion to species identification in this group of comb jellies.

Our revisions suggest the following systematic changes: (1) re-naming of the species from what was initially labelled as Beroe ovata, and later as B. cucumis (sensuMayer, 1912), to Beroe pseudocucumis sp. nov.. (2) Beroe mitrata but not Beroe ‘anatoliensis’ inhabits the Aegean Sea, as was reported previously. (3) Beroe ovata is the only species of Beroidae that became invasive and should be used with the authority of Bruguière, 1789, but not in the sense of Mayer, 1912. (4) Beroe forskalii appears to be represented by two species in the Mediterranean and in the Antarctic, but further justification is needed. (5) Beroe cucumis is a species of bipolar occurrence, inhabiting both subpolar areas and its recent definition as Beroe ‘norvegica’ is incorrect.