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Cnidarians are critical members of aquatic communities and have been an experimental system for a diversity of research areas ranging from development to biomechanics to global change biology. Yet, we still lack a well-resolved, taxonomically balanced cnidarian tree of life to place this research in appropriate phylogenetic context. To move towards this goal, we combined data from 26 new anthozoan transcriptomes with 86 previously published cnidarian and outgroup datasets to generate two 748-locus alignments containing 123,051 (trimmed) and 449,935 (untrimmed) amino acids. We estimated maximum likelihood phylogenies for both matrices under partitioned and unpartitioned site-homogeneous and site-heterogenous models of substitution. We used the resulting topology to constrain a phylogenetic analysis of 1,814 small subunit ribosomal (18S) gene sequences from GenBank. Our results confirm the position of Ceriantharia (tube-dwelling anemones), a historically recalcitrant group, as sister to the rest of Hexacorallia across all phylogenies regardless of data matrix or model choice. We find unanimous support for the sister relationships of Scleractinia and Corallimorpharia and of Endocnidozoa and Medusozoa. We propose the name Coralliformes for the clade uniting scleractinians and corallimorpharians and the name Operculozoa for the clade uniting endocnidozoans and medusozoans. Of the 229 genera with more than a single representative in our 18S hybrid phylogeny, 47 (21%) were identified as monophyletic, providing a starting point for a number of taxonomic revisions. Together, these data are an invaluable resource for comparative cnidarian research and provide perspective to guide future refinement of cnidarian systematics. 

Abstract The mutualism between clownfishes (or anemonefishes) and their giant host sea anemones are among the most immediately recognizable animal interactions on the planet and have attracted a great deal of popular and scientific attention [1-5]. However, our evolutionary understanding of this iconic symbiosis comes almost entirely from studies on clownfishes— a charismatic group of 28 described species in the genusAmphiprion[2]. Adaptation to venomous sea anemones (Anthozoa: Actiniaria) provided clownfishes with novel habitat space, ultimately triggering the adaptive radiation of the group [2]. Clownfishes diverged from their free-living ancestors 25-30 MYA with their adaptive radiation to sea anemones dating to 13.2 MYA [2, 3]. Far from being mere habitat space, the host sea anemones also receive substantial benefits from hosting clownfishes, making the mutualistic and co-dependent nature of the symbiosis well established [4, 5]. Yet the evolutionary consequences of mutualism with clownfishes have remained a mystery from the host perspective. Here we use bait-capture sequencing to fully resolve the evolutionary relationships among the 10 nominal species of clownfish-hosting sea anemones for the first time (Figure 1). Using time-calibrated divergence dating analyses we calculate divergence times of less than 25 MYA for each host species, with 9 of 10 host species having divergence times within the last 13 MYA (Figure 1). The clownfish-hosting sea anemones thus diversified coincidently with clownfishes, potentially facilitating the clownfish adaptive radiation, and providing the first strong evidence for co-evolutionary patterns in this iconic partnership. 

Abstract Cnidocytes are the explosive stinging cells unique to cnidarians (corals, jellyfish, etc). Specialized for prey capture and defense, cnidocytes comprise a group of over 30 morphologically and functionally distinct cell types. These unusual cells are iconic examples of biological novelty but the developmental mechanisms driving diversity of the stinging apparatus are poorly characterized, making it challenging to understand the evolutionary history of stinging cells. Using CRISPR/Cas9-mediated genome editing in the sea anemoneNematostella vectensis, we show that a single transcription factor (NvSox2) acts as a binary switch between two alternative stinging cell fates. Knockout ofNvSox2causes a transformation of piercing cells into ensnaring cells, which are common in other species of sea anemone but appear to have been silenced inN. vectensis. These results reveal an unusual case of single-cell atavism and expand our understanding of the diversification of cell type identity. 

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No abstract available. 

The advent of next-generation sequencing has resulted in transcriptome-based approaches to investigate functionally significant biological components in a variety of non-model organism. This has resulted in the area of “venomics”: a rapidly growing field using combined transcriptomic and proteomic datasets to characterize toxin diversity in a variety of venomous taxa. Ultimately, the transcriptomic portion of these analyses follows very similar pathways after transcriptome assembly often including candidate toxin identification using BLAST, expression level screening, protein sequence alignment, gene tree reconstruction, and characterization of potential toxin function. Here we describe the Python package Venomix, which streamlines these processes using common bioinformatic tools along with ToxProt, a publicly available annotated database comprised of characterized venom proteins. In this study, we use the Venomix pipeline to characterize candidate venom diversity in four phylogenetically distinct organisms, a cone snail (Conidae; Conus sponsalis ), a snake (Viperidae; Echis coloratus ), an ant (Formicidae; Tetramorium bicarinatum ), and a scorpion (Scorpionidae; Urodacus yaschenkoi ). Data on these organisms were sampled from public databases, with each original analysis using different approaches for transcriptome assembly, toxin identification, or gene expression quantification. Venomix recovered numerically more candidate toxin transcripts for three of the four transcriptomes than the original analyses and identified new toxin candidates. In summary, we show that the Venomix package is a useful tool to identify and characterize the diversity of toxin-like transcripts derived from transcriptomic datasets. Venomix is available at: https://bitbucket.org/JasonMacrander/Venomix/ .