Beauty in the beast - Placozoan biodiversity explored through molluscan predator genomics.

The marine animal phylum Placozoa is characterized by a poorly explored cryptic biodiversity combined with very limited knowledge of their ecology. While placozoans are typically found as part of the epibenthos of coastal waters, known placozoan predators, namely small, shell-less sea slugs belonging to the family Rhodopidae (Mollusca: Gastropoda: Heterobranchia), inhabit the interstitium of seafloor sediment. In order to gain further insights into this predator-prey relationship and to expand our understanding of placozoan ecological niches, we screened publicly available whole-body metagenomic data from two rhodopid specimens collected from coastal sediments.

Studying Placozoa WBR in the Simplest Metazoan Animal, Trichoplax adhaerens.

Placozoans are a promising model system to study fundamental regeneration processes in a morphologically and genetically very simple animal. We here provide a brief introduction to the enigmatic Placozoa and summarize the state of the art of animal handling and experimental manipulation possibilities.

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.

The first complete mitochondrial genome of the migratory dragonfly Fabricius, 1798 (Libellulidae: Odonata).

is the world's most abundant and widely distributed dragonfly and with its outstanding migratory capacity an important model system to study insect migration at the evolutionary base of winged insects. We here report on the first complete mitochondrial genome (mitogenome) of sampled from a population in Rufiji River, Tanzania. The mitogenome is 14,853 bp long with an AT-biased base composition (72.

Mitochondrial Genome Evolution of Placozoans: Gene Rearrangements and Repeat Expansions.

Placozoans, nonbilaterian animals with the simplest known metazoan bauplan, are currently classified into 20 haplotypes belonging to three genera, Polyplacotoma, Trichoplax, and Hoilungia. The latter two comprise two and five clades, respectively. In Trichoplax and Hoilungia, previous studies on six haplotypes belonging to four different clades have shown that their mtDNAs are circular chromosomes of 32-43 kb in size, which encode 12 protein-coding genes, 24 tRNAs, and two rRNAs.

Genome analyses of a placozoan rickettsial endosymbiont show a combination of mutualistic and parasitic traits.

Symbiotic relationships between eukaryotic hosts and bacteria range from parasitism to mutualism and may deeply influence both partners' fitness. The presence of intracellular bacteria in the metazoan phylum Placozoa has been reported several times, but without any knowledge about the nature of this relationship and possible implications for the placozoan holobiont. This information may be of crucial significance since little is known about placozoan ecology and how different species adapt to different environmental conditions, despite being almost invariable at the morphological level.

Polyplacotoma mediterranea is a new ramified placozoan species.

The enigmatic phylum Placozoa is harboring an unknown number of cryptic species and has become a challenge for modern systematics. Only recently, a second species has been described [1], while the presence of more than a hundred additional species has been suggested [2]. The original placozoan species Trichoplax adhaerens[3], the second species Hoilungia hongkongensis[1] and all yet undescribed species are morphologically indistinguishable (i.

Correction: Comparative genomics and the nature of placozoan species.

[This corrects the article DOI: 10.1371/journal.pbio.

Comparative genomics and the nature of placozoan species.

Placozoans are a phylum of nonbilaterian marine animals currently represented by a single described species, Trichoplax adhaerens, Schulze 1883. Placozoans arguably show the simplest animal morphology, which is identical among isolates collected worldwide, despite an apparently sizeable genetic diversity within the phylum. Here, we use a comparative genomics approach for a deeper appreciation of the structure and causes of the deeply diverging lineages in the Placozoa.

Trichoplax genomes reveal profound admixture and suggest stable wild populations without bisexual reproduction.

The phylum Placozoa officially consists of only a single described species, Trichoplax adhaerens, although several lineages can be separated by molecular markers, geographical distributions and environmental demands. The placozoan 16S haplotype H2 (Trichoplax sp. H2) is the most robust and cosmopolitan lineage of placozoans found to date.

Deep RNA sequencing reveals the smallest known mitochondrial micro exon in animals: The placozoan cox1 single base pair exon.

The phylum Placozoa holds a key position for our understanding of the evolution of mitochondrial genomes in Metazoa. Placozoans possess large mitochondrial genomes which harbor several remarkable characteristics such as a fragmented cox1 gene and trans-splicing cox1 introns. A previous study also suggested the existence of cox1 mRNA editing in Trichoplax adhaerens, yet the only formally described species in the phylum Placozoa.

The most primitive metazoan animals, the placozoans, show high sensitivity to increasing ocean temperatures and acidities.

The increase in atmospheric carbon dioxide (CO) leads to rising temperatures and acidification in the oceans, which directly or indirectly affects all marine organisms, from bacteria to animals. We here ask whether the simplest-and possibly also the oldest-metazoan animals, the placozoans, are particularly sensitive to ocean warming and acidification. Placozoans are found in all warm and temperate oceans and are soft-bodied, microscopic invertebrates lacking any calcified structures, organs, or symmetry.

The complete mitochondrial genome of the emperor dragonfly LEACH, 1815 (Odonata : Aeshnidae) via NGS sequencing.

Here we report the complete mitochondrial genome of the emperor dragonfly, (Odonata: Aeshnidae) as the first of its genus. Data were generated via next generation sequencing (NGS) and assembled using an iterative approach. The typical metazoan set of 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes) was detected in the same gene order as in other odonate mitogenomes.

Short read sequencing assembly revealed the complete mitochondrial genome of Vander Linden, 1820 (Odonata: Zygoptera).

Damselflies of the genus emerge as organisms with high potential in ecological, evolutionary and developmental research at the base of flying insects. and are for example one of the few odonate species where a complete life cycle over generations can be reared under laboratory conditions. We here report the complete mitochondrial genome of as a valuable genomic resource for future eco-evo-devo studies at the base of flying insects.

The complete mitochondrial genome of the neotropical helicopter damselfly (Odonata: Zygoptera) assembled from next generation sequencing data.

Odonata (dragonflies and damselflies) is a small order at the base of flying insects (Pterygota). Resolving family-level phylogenetic relationships within this order receives great attention. Hereby, genetic data already resulted in various changes, which are however still under discussion.

Mitogenomics at the base of Metazoa.

Unraveling the base of metazoan evolution is of crucial importance for rooting the metazoan Tree of Life. This subject has attracted substantial attention for more than a century and recently fueled a burst of modern phylogenetic studies. Conflicting scenarios from different studies and incongruent results from nuclear versus mitochondrial markers challenge current molecular phylogenetic approaches.

Global diversity of the Placozoa.

The enigmatic animal phylum Placozoa holds a key position in the metazoan Tree of Life. A simple bauplan makes it appear to be the most basal metazoan known and genetic evidence also points to a position close to the last common metazoan ancestor. Trichoplax adhaerens is the only formally described species in the phylum to date, making the Placozoa the only monotypic phylum in the animal kingdom.

Chasing the urmetazoon: striking a blow for quality data?

The ever-lingering question: "What did the urmetazoan look like?" has not lost its charm, appeal or elusiveness for one and a half centuries. A solid amount of organismal data give what some feel is a clear answer (e.g.

Concatenated analysis sheds light on early metazoan evolution and fuels a modern "urmetazoon" hypothesis.

For more than a century, the origin of metazoan animals has been debated. One aspect of this debate has been centered on what the hypothetical "urmetazoon" bauplan might have been. The morphologically most simply organized metazoan animal, the placozoan Trichoplax adhaerens, resembles an intriguing model for one of several "urmetazoon" hypotheses: the placula hypothesis.