A comparison of the structure and function of nematocysts in free-living and parasitic cnidarians (Myxozoa).

Myxozoans are obligate parasites that have complex life cycles requiring alternate vertebrate and invertebrate hosts, with transmission via microscopic waterborne spores. Unusually for parasites, they belong to the phylum Cnidaria, alongside thousands of free-living corals, sea anemones, jellyfish and hydrozoans. Their cnidarian affinity is affirmed by genetic relatedness and the presence of nematocysts, historically called "polar capsules" in myxozoan research. Free-living cnidarians utilise this cellular weaponry for defence, predation and adhesion, whereas myxozoans use it to anchor to their hosts as the first step in infection. Despite the ~650 million years of divergence between free-living cnidarians and myxozoans, their nematocysts retain many shared morphological and molecular characters. Both are intra-cellular capsules with a single opening, and contain a coiled, evertable tubule. They are composed of unique nematocyst proteins, nematogalectin and minicollagen, and both likely contain an internal matrix of metal cations covalently bound to the anionic polymer poly-gamma glutamate. The rapid dissociation of this matrix and the resulting increase in internal osmotic potential is the driving force behind tubule elongation during discharge. In this review, we compare the structure and function of nematocysts in Myxozoa and free-living Cnidaria, incorporating recent molecular characterizations. We propose that terminology for homologous myxozoan structures be synonymized with those from other Cnidaria, hence, "polar capsule" as a taxon-specific nematocyst morphotype and "polar filament" as "tubule." Despite taxonomic divergence, genome reduction and an evolution to parasitism, myxozoans maintain nematocysts that are structurally and functionally homologous to those of their free-living cnidarian relatives.

Venom Composition Does Not Vary Greatly Between Different Nematocyst Types Isolated from the Primary Tentacles of Olindias sambaquiensis (Cnidaria: Hydrozoa).

In this quantitative proteomics study we determined the variety and relative abundance of toxins present in enriched preparations of two nematocyst types isolated from the primary tentacles of the adult medusa stage of the hydrozoan Olindias sambaquiensis. The two nematocyst types were microbasic mastigophores and microbasic euryteles, and these were recovered from the macerated tentacle tissues by using a differential centrifugation approach. Soluble protein extracts from these nematocysts were tagged with tandem mass tag isobaric labels and putative toxins identified using tandem mass spectrometry coupled with a stringent bioinformatics annotation pipeline. Astonishingly, the venom composition of the two capsule types was nearly identical, and there was also little difference in the comparative abundance of toxins between the two nematocyst preparations. This homogeneity suggested that the same toxin complement was present regardless of the penetrative ability of the nematocyst type. Predicted toxin protein families that constituted the venom closely matched those of the toxic proteome of O. sambaquiensis published four years previously, suggesting that venom composition in this species changes little over time. Retaining an array of different nematocyst types to deliver a single venom, rather than sustaining the high metabolic cost necessary to maintain a dynamically evolving venom, may be more advantageous, given the vastly different interspecific interactions that adult medusa encounter in coastal zones.

The nematocyst's sting is driven by the tubule moving front.

The nematocyst is the explosive injection system of the phylum Cnidaria, and is one of the fastest delivery systems found in Nature. Exploring its injection mechanism is key for understanding predator-prey interactions and protection against jellyfish stinging. Here we analyse the injection of jellyfish nematocysts and ask how the build-up of the poly-γ-glutamate (pγGlu) osmotic potential inside the nematocyst drives its discharge. To control the osmotic potential, we used a two-channel microfluidic system to direct the elongating nematocyst tubule through oil, where no osmotic potential can develop, while keeping the nematocyst capsule in water at all times. In addition, the flow inside the tubule and the pγGlu concentration profiles were calculated by applying a one-dimensional mathematical model. We found that tubule elongation through oil is orders of magnitude slower than through water and that the injection rate of the nematocyst content is reduced. These results imply that the capsule's osmotic potential is not sufficient to drive the tubule beyond the initial stage. Our proposed model shows that the tubule is pulled by the high osmotic potential that develops at the tubule moving front. This new understanding is vital for future development of nematocyst-based systems such as osmotic nanotubes and transdermal drug delivery.

Length Is Associated with Pain: Jellyfish with Painful Sting Have Longer Nematocyst Tubules than Harmless Jellyfish.

A large number of humans are stung by jellyfish all over the world. The stings cause acute pain followed by persistent pain and local inflammation. Harmful jellyfish species typically cause strong pain, whereas harmless jellyfish cause subtle or no pain. Jellyfish sting humans by injecting a tubule, contained in the nematocyst, the stinging organ of jellyfish. The tubule penetrates into the skin leading to venom injection. The detailed morphology of the nematocyst tubule and molecular structure of the venom in the nematocyst has been reported; however, the mechanism responsible for the difference in pain that is caused by harmful and harmless jellyfish sting has not yet been explored or explained. Therefore, we hypothesized that differences in the length of the nematocyst tubule leads to different degrees of epithelial damage. The initial acute pain might be generated by penetration of the tubule, which stimulates pain receptor neurons, whilst persistent pain might be caused by injection of venom into the epithelium. To test this hypothesis we compared the lengths of discharged nematocyst tubules from harmful and harmless jellyfish species and evaluated their ability to penetrate human skin. The results showed that the harmful jellyfish species, Chrysaora pacifica, Carybdea brevipedalia, and Chironex yamaguchii, causing moderate to severe pain, have nematocyst tubules longer than 200 µm, compared with a jellyfish species that cause little or no pain, Aurelia aurita. The majority of the tubules of harmful jellyfishes, C. yamaguchii and C. brevipedalia, were sufficiently long to penetrate the human epidermis and physically stimulate the free nerve endings of Aδ pain receptor fibers around plexuses to cause acute pain and inject the venom into the human skin epithelium to cause persistent pain and inflammation.

Prey Capture Ecology of the Cubozoan Carukia barnesi.

Adult Carukia barnesi medusae feed predominantly on larval fish; however, their mode of prey capture seems more complex than previously described. Our findings revealed that during light conditions, this species extends its tentacles and 'twitches' them frequently. This highlights the lure-like nematocyst clusters in the water column, which actively attract larval fish that are consequently stung and consumed. This fishing behavior was not observed during dark conditions, presumably to reduce energy expenditure when they are not luring visually oriented prey. We found that larger medusae have longer tentacles; however, the spacing between the nematocyst clusters is not dependent on size, suggesting that the spacing of the nematocyst clusters is important for prey capture. Additionally, larger specimens twitch their tentacles more frequently than small specimens, which correlate with their recent ontogenetic prey shift from plankton to larval fish. These results indicate that adult medusae of C. barnesi are not opportunistically grazing in the water column, but instead utilize sophisticated prey capture techniques to specifically target larval fish.

Catostylus tagi: partial rDNA sequencing and characterisation of nematocyte structures using two improvements in jellyfish sample preparation

Background More than 200 Scyphozoa species have been described, but few have been properly studied regarding their chemical and genetic characteristics.Catostylus tagi, an edible Scyphozoa and the sole European Catostylidae, occurs in summer at Tagus and Sado estuaries. Neither a systematic comparison between the two Catostyluscommunities nor a chemical approach on their nematocytes had been carried out yet.Methods In order to achieve these purposes, optimisation of DNA extraction and of histochemical staining procedures were developed.Catostylus specimens from Tagus and Sado estuaries were compared by ribosomal 18S, 28S, and ITS1 partial sequencing. The morphochemistry of nematocytes was studied by optical and electronic microscopy.Results Macroscopic and molecular results indicated that both communities belong to the same species, C. tagi. The hematoxylin and eosin staining allowed the visualisation of nematocyst genesis and indicated a basic character for the macromolecules on the shaft of euryteles and on the tubule of isorhizae and birhopaloids. By Massons trichrome procedure, the basic properties of the tubules were confirmed and a collagenous profile for the toxins was suggested. Results of the alcian blue staining showed that the outer membrane of nematocyte may consist of macromolecules with acidic polysaccharides, consistent with NOWA and nematogalectin glycoproteins detected in Hydra, but also with poly-gamma-glutamate complex, chitin-like polysaccharides and hyaluronic acids. Through the von Kossa assays, calcium was detected; its position suggested interactions with polysaccharides of the membrane, with proteins of the contractile system or with both.Conclusions The optimisation of sample preparation for DNA extraction may facilitate further studies on little known jellyfish species. The improvement of the smear procedure simplified the use of stained reactions in zooplankton. Moreover, it was shown that good slide images might be acquired manually. The development of specific reactions, with traditional dyes and others, can give important contributions to clarify the chemical nature of the components of nematocytes. The characterisation of nematocyst toxins by staining tests is a goal to achieve.

Internal anatomy of Haliclystus antarcticus (Cnidaria, Staurozoa) with a discussion on histological features used in Staurozoan taxonomy.

Stauromedusae have relatively few macromorphological characters, making both their taxonomy and identification difficult. For this reason, histological characters are also employed in the taxonomy of the group. This study presents a detailed description of the histomorphology of Haliclystus antarcticus Pfeffer, 1889 (Cnidaria, Staurozoa). We make new observations for the species and for the class, and address functional, taxonomical, and evolutionary aspects of staurozoan histo-anatomy. A complete reconstruction of H. antarcticus body plan is used to guide a more detailed observation, based on light microscopy, of structures rarely cited in the literature, such as the intertentacular lobules, the ostia between adjacent perradial pockets, and the male and female gonadal vesicles. Two possible regions of nematocyst formation are hypothesized and discussed. We also provide a review of the current use of histological characters in the taxonomy of the group. Understanding the body plan of stauromedusae is a challenge, because each single individual presents characters found in medusae and in polyps of other medusozoans. Comprehensive histological descriptions are important to establish relations of homology within Staurozoa and Cnidaria, providing crucial data on their evolution.

Nematocysts of the invasive hydroid Cordylophora caspia (Cnidaria: Hydrozoa).

Although there is significant genetic diversity among populations of the hydroid Cordylophora caspia, the species has not been split into multiple species or subspecies, in part because its members also show great physiological and morphological plasticity. This plasticity makes new taxonomic units hard to define or identify and obscures the connection between historically used names and the genetically defined clades. We explore variation in nematocysts, a character system not previously assessed in Cordylophora but which has demonstrated phylogenetic signal in other cnidarian taxa. We measured more than 5000 capsules from 112 individuals belonging to 14 populations, including representatives of the major genetic lineages. We found no correlation between the size range of capsules and either clade or salinity. Thus, for C. caspia, nematocysts are neither phenotypically plastic with respect to salinity nor taxonomically informative. Nematocyst size and density in particular tissues may be correlated to other environmental factors (such as prey type, size, and abundance in the location of each population) and may aid in distinguishing more distantly related species.

Re-evaluation of characters in Apolemiidae (Siphonophora), with description of two new species from Monterey Bay, California.

Siphonophores are polymorphic planktonic marine Cnidarians. The family Apolemiidae is sister to all other species of physonect and calycophoran siphonophores. Although this enigmatic group arguably includes the longest animal species on the planet, their colony-level organization and growth patterns are not well understood. Here we describe two new apolemiid species: Apolemia lanosa sp. nov. and A. rubriversa sp. nov. We provide detailed descriptions of zooid budding and the organization of mature zooids within the siphosome. Our findings reveal that at least two distinct general patterns of siphosomal organization are found in different Apolemia species. In the first pattern, dispersed organization, zooids independently attach directly to the siphosomal stem. In the second pattern, pedunculate organization, only the gastrozooid is attached directly to the stem, and the other zooids of the cormidium branch from its peduncle. This diversity within Apolemia indicates that fundamental aspects of zooid budding and organization are homoplastic within Siphonophora, as both patterns are also found in other siphonophores. The observations presented here greatly clarify the interpretation of diagnostic characters within Apolemiidae, bear on the status of the three previously described species, provide critical detail for understanding the diversity of colony-level organization in siphonophores, and establish a foundation for the description of additional apolemiid species.

Morphological and molecular analysis of the Nematostella vectensis cnidom.

The starlet sea anemone Nematostella vectensis is an emerging model organism for developmental and evolutionary biology. Due to the availability of genome data and its amenability to genetic manipulation Nematostella serves as a source for comparative molecular and phylogenetic studies. Despite this fact, the characterization of the nematocyst inventory and of nematocyst-specific genes is still fragmentary and sometimes misleading in this cnidarian species. Here, we present a thorough qualitative and quantitative analysis of nematocysts in Nematostella vectensis. In addition, we have cloned major nematocyst components, Nematostella minicollagens 1, 3 and 4, and show their expression patterns by in situ hybridization and immunocytochemistry using specific antibodies. Our data provides tools and insights for further studies on nematocyst morphogenesis in Nematostella and comparative evolution in cnidarians.

Partial characterization of the hemolytic activity of the nematocyst venom from the jellyfish Cyanea nozakii Kishinouye.

Using a recently developed technique to extract jellyfish venom from nematocysts, the present study investigated the hemolytic activity of Cyanea nozakii Kishinouye nematocyst venom on chicken erythrocytes. Venom extract caused a significant concentration-dependent hemolytic effect. The extract could retain its activity at -80 degrees C but was unstable when kept at 4 degrees C and -20 degrees C for 2 days. The hemolytic activity was inhibited by heating within the range of 37-100 degrees C. The extract was active over a pH range of 5.0-8.63 and the pH optima for the extract was 7.8. Incubation of the venom with sphingomyelin specially inhibited hemolytic activity by up to 70%. Cu(2+) and Mn(2+) greatly reduced the hemolytic activity while Mg(2+), Sr(2+) and Ba(2+) produced a relatively low inhibiting effect on the hemolytic activity. Treatment with Ca(2+) induced a concentration-dependent increase in the hemolytic activity. In the presence of 5 mM EDTA, all the hemolytic activity was lost, however, the venom containing 1.5 mM EDTA was stable in the long-term storage. PLA(2) activity was also found in the nematocyst venom of C. nozakii. These characteristics provide us a fundamental knowledge in the C. nozakii nematocyst venom which would benefit future research.