Cnidarians are the oldest extant lineage of venomous animals. Despite their simple anatomy, they are capable of subduing or repelling prey and predator species that are far more complex and recently evolved. Utilizing specialized penetrating nematocysts, cnidarians inject the nematocyst content or “venom” that initiates toxic and immunological reactions in the envenomated organism. These venoms contain enzymes, potent pore forming toxins, and neurotoxins. Enzymes include lipolytic and proteolytic proteins that catabolize prey tissues. Cnidarian pore forming toxins self-assemble to form robust membrane pores that can cause cell death via osmotic lysis. Neurotoxins exhibit rapid ion channel specific activities. In addition, certain cnidarian venoms contain or induce the release of host vasodilatory biogenic amines such as serotonin, histamine, bunodosine and caissarone accelerating the pathogenic effects of other venom enzymes and porins. The cnidarian attacking/defending mechanism is fast and efficient, and massive envenomation of humans may result in death, in some cases within a few minutes to an hour after sting. The complexity of venom components represents a unique therapeutic challenge and probably reflects the ancient evolutionary history of the cnidarian venom system. Thus, they are invaluable as a therapeutic target for sting treatment or as lead compounds for drug design.

Cubozoa (Cnidaria: Medusozoa) represents a small clade of approximately 50 described species, some of which cause serious human envenomations. Our understanding of the evolutionary history of Cubozoa has been limited by the lack of a sound phylogenetic hypothesis for the group. Here, we present a comprehensive cubozoan phylogeny based on ribosomal genes coding for near-complete nuclear 18S (small subunit) and 28S (large subunit) and partial mitochondrial 16S. We discuss the implications of this phylogeny for our understanding of cubozoan venom evolution, biogeography and life-history evolution. Our phylogenetic hypothesis suggests that: (i) the last common ancestor of Carybdeida probably possessed the mechanism(s) underlying Irukandji syndrome, (ii) deep divergences between Atlantic and Indo-Pacific clades may be explained by ancient vicariant events, and (iii) sexual dimorphism evolved a single time in concert with complex sexual behaviour. Furthermore, several cubozoan taxa are either para-or polyphyletic, and we address some of these taxonomic issues by designating a new family, Carukiidae, a new genus, Copula, and by redefining the families Tamoyidae and Tripedaliidae. Lastly, cubozoan species identities have long been misunderstood and the data presented here support many of the recent scientific descriptions of cubozoan species. However, the results of a phylogeographic analysis of Alatina moseri from Hawai'i and Alatina mordens from Australia indicate that these two nominal species represent a single species that has maintained metapopulation cohesion by natural or anthropogenic dispersal.

Just over a century ago, animal responses to injections of jellyfish extracts unveiled the phenomenon of anaphylaxis. Yet, until very recently, understanding of jellyfish sting toxicity has remained limited. Upon contact, jellyfish stinging cells discharge complex venoms, through thousands of barbed tubules, into the skin resulting in painful and, potentially, lethal envenomations. This review examines the immunological and toxinological responses to stings by prominent species of jellyfish including Physalia sp. (Portuguese Man-o-War, Blue-bottle), Cubozoan jellyfish including Chironex fleckeri, several Carybdeids including Carybdea arborifera and Alatina moseri, Linuche unguiculta (Thimble jellyfish), a jellyfish responsible for Irukandji syndrome (Carukia barnesi) and Pelagia noctiluca. Jellyfish venoms are composed of potent proteinaceous porins (cellular membrane pore-forming toxins), neurotoxic peptides, bioactive lipids and other small molecules whilst the tubules contain ancient collagens and chitins. We postulate that immunologically, both tubular structural and functional biopolymers as well as venom components can initiate innate, adaptive, as well as immediate and delayed hypersensitivity reactions that may be amenable to topical anti-inflammatory-immunomodifier therapy. The current challenge for immunotoxinologists is to deconstruct the actions of venom components to target therapeutic modalities for sting treatment.

Hydrozoans display the most morphological diversity within the phylum Cnidaria. While recent molecular studies have provided some insights into their evolutionary history, sister group relationships remain mostly unresolved, particularly at mid-taxonomic levels. Specifically, within Hydroidolina, the most speciose hydrozoan subclass, the relationships and sometimes integrity of orders are highly unsettled. Here we obtained the near complete mitochondrial sequence of twenty-six hydroidolinan hydrozoan species from a range of sources (DNA and RNA-seq data, long-range PCR). Our analyses confirm previous inference of the evolution of mtDNA in Hydrozoa while introducing a novel genome organization. Using RNA-seq data, we propose a mechanism for the expression of mitochondrial mRNA in Hydroidolina that can be extrapolated to the other medusozoan taxa. Phylogenetic analyses using the full set of mitochondrial gene sequences provide some insights into the order-level relationships within Hydroidolina, including siphonophores as the first diverging clade, a well-supported clade comprised of Leptothecata-Filifera III–IV, and a second clade comprised of Aplanulata-Capitata s.s.-Filifera I–II. Finally, we describe our relatively inexpensive and accessible multiplexing strategy to sequence long-range PCR amplicons that can be adapted to most high-throughput sequencing platforms.

Animal mitochondrial DNAs (mtDNAs) are typically single circular chromosomes, with the exception of those from medusozoan cnidarians (jellyfish and hydroids), which are linear and sometimes fragmented. Most medusozoans have linear monomeric or linear bipartite mitochondrial genomes, but preliminary data have suggested that box jellyfish (cubozoans) have mtDNAs that consist of many linear chromosomes. Here, we present the complete mtDNA sequence from the winged box jellyfish Alatina moseri (the first from a cubozoan). This genome contains unprecedented levels of fragmentation: 18 unique genes distributed over eight 2.9- to 4.6-kb linear chromosomes. The telomeres are identical within and between chromosomes, and recombination between subtelomeric sequences has led to many genes initiating or terminating with sequences from other genes (the most extreme case being 150 nt of a ribosomal RNA containing the 5′ end of nad2), providing evidence for a gene conversion–based model of telomere evolution. The silent-site nucleotide variation within the A. moseri mtDNA is among the highest observed from a eukaryotic genome and may be associated with elevated rates of recombination.

Chironex fleckeri (Australian box jellyfish) stings can cause acute cardiovascular collapse and death. We developed methods to recover venom with high specific activity, and evaluated the effects of both total venom and constituent porins at doses equivalent to lethal envenomation. Marked potassium release occurred within 5 min and hemolysis within 20 min in human red blood cells (RBC) exposed to venom or purified venom porin. Electron microscopy revealed abundant ∼12-nm transmembrane pores in RBC exposed to purified venom porins. C57BL/6 mice injected with venom showed rapid decline in ejection fraction with progression to electromechanical dissociation and electrocardiographic findings consistent with acute hyperkalemia. Recognizing that porin assembly can be inhibited by zinc, we found that zinc gluconate inhibited potassium efflux from RBC exposed to total venom or purified porin, and prolonged survival time in mice following venom injection. These findings suggest that hyperkalemia is the critical event following Chironex fleckeri envenomation and that rapid administration of zinc could be life saving in human sting victims.

Despite the medical urgency presented by cubozoan envenomations, ineffective and contradictory first-aid management recommendations persist. A critical barrier to progress has been the lack of readily available and reproducible envenomation assays that (1) recapitulate live-tentacle stings; (2) allow quantitation and imaging of cnidae discharge; (3) allow primary quantitation of venom toxicity; and (4) employ rigorous controls. We report the implementation of an integrated array of three experimental approaches designed to meet the above-stated criteria. Mechanistically overlapping, yet distinct, the three approaches comprised (1) direct application of test solutions on live tentacles (termed tentacle solution assay, or TSA) with single image- and video-microscopy; (2) spontaneous stinging assay using freshly excised tentacles overlaid on substrate of live human red blood cells suspended in agarose (tentacle blood agarose assays, or TBAA); and (3) a “skin” covered adaptation of TBAA (tentacle skin blood agarose assay, or TSBAA). We report the use and results of these assays to evaluate the efficacy of topical first-aid approaches to inhibit tentacle firing and venom activity. TSA results included the potent stimulation of massive cnidae discharge by alcohols but only moderate induction by urine, freshwater, and “cola” (carbonated soft drink). Although vinegar, the 40-year field standard of first aid for the removal of adherent tentacles, completely inhibited cnidae firing in TSA and TSBAA ex vivo models, the most striking inhibition of both tentacle firing and subsequent venom-induced hemolysis was observed using newly-developed proprietary formulations (Sting No More™) containing copper gluconate, magnesium sulfate, and urea.

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