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Simple Summary: This study investigated the nematocyst types found in the tentacles of box jellyfish Gershwinia thailandensis and Morbakka sp. in Thai waters, providing detailed taxonomic insights into these toxic stinging cells. Three nematocyst types were identified in both species: club-shaped microbasic p-mastigophores (Type 4), oval isorhizas, and oval microbasic p-rhopaloids. While the sizes of nematocyst capsules varied between species, the spination pattern of discharge tubules was consistent. These differences in nematocyst types, population densities, and morphologies may indicate evolutionary adaptations and functional specialization. Understanding these distinctions could aid in developing species-specific envenomation treatments and deepen our knowledge of the ecological and toxicological roles of these nematocysts. Further research on the molecular composition and venom release mechanisms will offer valuable biological insights. Nematocysts, specialized stinging cells in cnidarians, play a crucial role in both defense and prey capture, containing venomous, coiled tubes within a capsule. While box jellyfish are recognized as a medical threat, information on the nematocysts of species like Gershwinia thailandensis and Morbakka sp. from Thai waters remains sparse. This study explores the types and morphology of nematocysts found in the tentacles of these species using light and scanning electron microscopy. We identified three nematocyst types: club-shaped microbasic p-mastigophores, oval isorhizas, and oval microbasic p-rhopaloids. Notably, significant differences in capsule sizes were observed, especially in the microbasic p-mastigophores and isorhizas. The discharge tubules tapered from the proximal to the distal ends, featuring arrow-shaped spines in a helical pattern. A distinct lancet structure was present in both microbasic p-mastigophores and p-rhopaloids. These findings suggest that variations in nematocyst size and morphology may be linked to evolutionary adaptations, functional roles, and venom toxicity. Further research into venom discharge mechanisms could offer valuable insights into the ecological and medical importance of these cnidarians. [ABSTRACT FROM AUTHOR]

The substantial development of microscopic techniques and histological examination methods during the past five decades allowed for many new insights into the histology and microanatomy of Rhizostomeae. The present review focuses on new findings about histologically important structures: nerves, senses, muscles, gonads, zooxanthellae and nematocysts. Different ontogenetic stages of rhizostome species were included in the literature research, supplemented with the authors' unpublished data and figures. The overview of the research results reveals that the application of chemo- and immunohistochemical techniques have provided deeper insights into neuronal and sensory structures and their interconnections. Modern microscopic methods led to new findings on the histological gonadal organization and details of the processes of gametogenesis, fertilization, cleavage, gastrulation, and brooding. Advanced optical methods also allowed for a better understanding of Rhizostomeae-zooxanthellae associations and the morphology and function of nematocysts. Improvements in molecular biology allowed for more precise identification of zooxanthellae associated with rhizostome species. Although there has been significant progress in all of the research subjects covered here, we identify several knowledge gaps and conclude with some recommendations for future research. [ABSTRACT FROM AUTHOR]

Nematocysts, specialized stinging cells in cnidarians, play a crucial role in both defense and prey capture, containing venomous, coiled tubes within a capsule. While box jellyfish are recognized as a medical threat, information on the nematocysts of species like Gershwinia thailandensis and Morbakka sp. from Thai waters remains sparse. This study explores the types and morphology of nematocysts found in the tentacles of these species using light and scanning electron microscopy. We identified three nematocyst types: club-shaped microbasic p-mastigophores, oval isorhizas, and oval microbasic p-rhopaloids. Notably, significant differences in capsule sizes were observed, especially in the microbasic p-mastigophores and isorhizas. The discharge tubules tapered from the proximal to the distal ends, featuring arrow-shaped spines in a helical pattern. A distinct lancet structure was present in both microbasic p-mastigophores and p-rhopaloids. These findings suggest that variations in nematocyst size and morphology may be linked to evolutionary adaptations, functional roles, and venom toxicity. Further research into venom discharge mechanisms could offer valuable insights into the ecological and medical importance of these cnidarians.

Complex biological traits often originate by integrating previously separate parts, but the organismal functions of these precursors are challenging to infer. If we can understand the ancestral functions of these precursors, it could help explain how they persisted and how they facilitated the origins of complex traits. Animal eyes are some of the best studied complex traits, and they include many parts, such as opsin-based photoreceptor cells, pigment cells, and lens cells. Eye evolution is understood through conceptual models that argue these parts gradually came together to support increasingly sophisticated visual functions. Despite the well-accepted logic of these conceptual models, explicit comparative studies to identify organismal functions of eye precursors are lacking. Here, we investigate how precursors functioned before they became part of eyes in Cnidaria, a group formed by sea anemones, corals, and jellyfish. Specifically, we test whether ancestral photoreceptor cells regulated the discharge of cnidocytes, the expensive single-use cells with various functions including prey capture, locomotion, and protection. Similar to a previous study of Hydra, we show an additional four distantly related cnidarian groups discharge significantly more cnidocytes when exposed to dim blue light compared with bright blue light. Our comparative analyses support the hypothesis that the cnidarian ancestor was capable of modulating cnidocyte discharge with light, which we speculate uses an opsin-based phototransduction pathway homologous to that previously described in Hydra. Although eye precursors might have had other functions like regulating timing of spawning, our findings are consistent with the hypothesis that photoreceptor cells which mediate cnidocyte discharge predated eyes, perhaps facilitating the prolific origination of eyes in Cnidaria.

Nudibranchs have a mostly carnivorous diet, and they prey on a wide variety of other animal taxa. Many species, mainly belonging to the Cladobranchia suborder, feed on cnidarians, including member of the class Hydrozoa. Several hydrozoan species display a symbiotic lifestyle, being associated with other benthic invertebrates, including for instance bryozoans, corals, octocorals, and sponges. In our knowledge, no record of nudibranch predation on symbiotic hydrozoans has been reported so far, possibly thanks to the protective action by the host towards its symbiotic hydrozoan. Here, we show the unexpected case of a nudibranch belonging to the recently described species Sakuraeolis marhe (Fernández-Simón and Moles, 2023) feeding on Zanclea sp. 2, a hydrozoan associated with the cheilostome bryozoan Celleporaria sp. This trophic association is confirmed by the presence and storage of the nematocysts into the nudibranch cnidosacs. Moreover, the nudibranch appears to selectively store mostly a single type of nematocyst, that is large size stenotele. The observation here reported represents the first well-documented record of a nudibranch feeding on a symbiotic hydrozoan and the first confirmed case of predation on Zanclea polyps. Moreover, we provide additional genetic information and the first description of the internal anatomy of S. marhe. [ABSTRACT FROM AUTHOR]

Abstract Background Intracellular sequestration requires specialized cellular and molecular mechanisms allowing a predator to retain and use specific organelles that once belonged to its prey. Little is known about how common cellular mechanisms, like phagocytosis, can be modified to selectively internalize and store foreign structures. One form of defensive sequestration involves animals that sequester stinging organelles (nematocysts) from their cnidarian prey. While it has been hypothesized that nematocysts are identified by specialized phagocytic cells for internalization and storage, little is known about the cellular and developmental mechanisms of this process in any metazoan lineage. This knowledge gap is mainly due to a lack of genetically tractable model systems among predators and their cnidarian prey. Results Here, we introduce the nudibranch Berghia stephanieae as a model system to investigate the cell, developmental, and physiological features of nematocyst sequestration selectivity. We first show that B. stephanieae, which feeds on Exaiptasia diaphana, selectively sequesters nematocysts over other E. diaphana tissues found in their digestive gland. Using confocal microscopy, we document that nematocyst sequestration begins shortly after feeding and prior to the formation of the appendages (cerata) where the organ responsible for sequestration (the cnidosac) resides in adults. This finding is inconsistent with previous studies that place the formation of the cnidosac after cerata emerge. Our results also show, via live imaging assays, that both nematocysts and dinoflagellates can enter the nascent cnidosac structure. This result indicates that selectivity for nematocysts occurs inside the cnidosac in B. stephanieae, likely in the cnidophage cells themselves. Conclusions Our work highlights the utility of B. stephanieae for future research, because: (1) this species can be cultured in the laboratory, which provides access to all developmental stages, and (2) the transparency of early juveniles makes imaging techniques (and therefore cell and molecular assays) feasible. Our results pave the way for future studies using live imaging and targeted gene editing to identify the molecular mechanisms involved in nematocyst sequestration. Further studies of nematocyst sequestration in B. stephanieae will also allow us to investigate how common cellular mechanisms like phagocytosis can be modified to selectively internalize and store foreign structures.

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Abstract Complex biological traits often originate by integrating previously separate parts, but the organismal functions of these precursors are challenging to infer. If we can understand the ancestral functions of these precursors, it could help explain how they persisted and how they facilitated the origins of complex traits. Animal eyes are some of the best studied complex traits, and they include many parts, such as opsin‐based photoreceptor cells, pigment cells, and lens cells. Eye evolution is understood through conceptual models that argue these parts gradually came together to support increasingly sophisticated visual functions. Despite the well‐accepted logic of these conceptual models, explicit comparative studies to identify organismal functions of eye precursors are lacking. Here, we investigate how precursors functioned before they became part of eyes in Cnidaria, a group formed by sea anemones, corals, and jellyfish. Specifically, we test whether ancestral photoreceptor cells regulated the discharge of cnidocytes, the expensive single‐use cells with various functions including prey capture, locomotion, and protection. Similar to a previous study of Hydra, we show an additional four distantly related cnidarian groups discharge significantly more cnidocytes when exposed to dim blue light compared with bright blue light. Our comparative analyses support the hypothesis that the cnidarian ancestor was capable of modulating cnidocyte discharge with light, which we speculate uses an opsin‐based phototransduction pathway homologous to that previously described in Hydra. Although eye precursors might have had other functions like regulating timing of spawning, our findings are consistent with the hypothesis that photoreceptor cells which mediate cnidocyte discharge predated eyes, perhaps facilitating the prolific origination of eyes in Cnidaria.

Nudibranchs have a mostly carnivorous diet, and they prey on a wide variety of other animal taxa. Many species, mainly belonging to the Cladobranchia suborder, feed on cnidarians, including member of the class Hydrozoa. Several hydrozoan species display a symbiotic lifestyle, being associated with other benthic invertebrates, including for instance bryozoans, corals, octocorals, and sponges. In our knowledge, no record of nudibranch predation on symbiotic hydrozoans has been reported so far, possibly thanks to the protective action by the host towards its symbiotic hydrozoan. Here, we show the unexpected case of a nudibranch belonging to the recently described species Sakuraeolis marhe (Fernández-Simón and Moles, 2023) feeding on Zanclea sp. 2, a hydrozoan associated with the cheilostome bryozoan Celleporaria sp. This trophic association is confirmed by the presence and storage of the nematocysts into the nudibranch cnidosacs. Moreover, the nudibranch appears to selectively store mostly a single type of nematocyst, that is large size stenotele. The observation here reported represents the first well-documented record of a nudibranch feeding on a symbiotic hydrozoan and the first confirmed case of predation on Zanclea polyps. Moreover, we provide additional genetic information and the first description of the internal anatomy of S. marhe.

Background: Intracellular sequestration requires specialized cellular and molecular mechanisms allowing a predator to retain and use specific organelles that once belonged to its prey. Little is known about how common cellular mechanisms, like phagocytosis, can be modified to selectively internalize and store foreign structures. One form of defensive sequestration involves animals that sequester stinging organelles (nematocysts) from their cnidarian prey. While it has been hypothesized that nematocysts are identified by specialized phagocytic cells for internalization and storage, little is known about the cellular and developmental mechanisms of this process in any metazoan lineage. This knowledge gap is mainly due to a lack of genetically tractable model systems among predators and their cnidarian prey. Results: Here, we introduce the nudibranch Berghia stephanieae as a model system to investigate the cell, developmental, and physiological features of nematocyst sequestration selectivity. We first show that B. stephanieae, which feeds on Exaiptasia diaphana, selectively sequesters nematocysts over other E. diaphana tissues found in their digestive gland. Using confocal microscopy, we document that nematocyst sequestration begins shortly after feeding and prior to the formation of the appendages (cerata) where the organ responsible for sequestration (the cnidosac) resides in adults. This finding is inconsistent with previous studies that place the formation of the cnidosac after cerata emerge. Our results also show, via live imaging assays, that both nematocysts and dinoflagellates can enter the nascent cnidosac structure. This result indicates that selectivity for nematocysts occurs inside the cnidosac in B. stephanieae, likely in the cnidophage cells themselves. Conclusions: Our work highlights the utility of B. stephanieae for future research, because: (1) this species can be cultured in the laboratory, which provides access to all developmental stages, and (2) the transparency of early juveniles makes imaging techniques (and therefore cell and molecular assays) feasible. Our results pave the way for future studies using live imaging and targeted gene editing to identify the molecular mechanisms involved in nematocyst sequestration. Further studies of nematocyst sequestration in B. stephanieae will also allow us to investigate how common cellular mechanisms like phagocytosis can be modified to selectively internalize and store foreign structures. [ABSTRACT FROM AUTHOR]

Although the biometric investigation of the cnidome represents an essential diagnostic feature to successfully identify cnidarian species, further efforts are needed to fully characterize eventual differences. Important model actiniarians, such Anemonia viridis and Aiptasia spp., are commonly used for scientific purposes; however, their identification is often difficult, and the description of their cnidome is, therefore, essential. To contribute to this necessity, specimens of Anemonia viridis and Aiptasia couchii from the North Adriatic Sea were collected to acquire data (i.e. length, width, size range, length/width ratio) about cnidae from different tissues (i.e. column, tentacles, actinopharynx, mesenteries, and acrorhagi/acontia). Four types of cnidae were observed in each species. A. viridis shows microbasic b-mastigophores, microbasic p-mastigophores, holotrichous isorhizas, and spirocysts, whereas A. couchii harbored basitrichs, microbasic p-mastigophore, microbasic p-amastigophore and spirocysts. Molecular and phylogenetic analyses were also performed using three mitochondrial markers to confirm the correct classification of the specimens here analysed. [ABSTRACT FROM AUTHOR]

The American ctenophore Mnemiopsis leidyi, recently found in Skagerrak off the Swedish west coast, carried parasitic anemone larvae identified as Edwardsiella sp. In the Western Atlantic Ocean, M. leidyi are commonly infected by larvae of American Edwardsiella lineata anemones. It was questioned whether the parasitic larvae came across the Atlantic with the invasive ctenophore, or whether they belonged to the native E. carnea anemones. However, recent molecular investigations identified E. carnea and E. lineata as different species and the Swedish larvae from M. leidyi as E. carnea. Present morphological investigation supports the distinction of E. carnea anemones from E. lineata by a changeable rounded to flattened physa without rugae and by white pigmentation on basal outer tentacles. One Swedish larva developed into a juvenile with this characteristic column differentiation, identifying our larva as E. carnea and confirming its ability to produce parasitic larvae. Cnidome descriptions of E. carnea anemones and larvae reveal three similar cnidae in E. carnea and E. lineata anemones and larvae, and cnidae specific to either anemone or larval stages. Cnidome characteristics support our parasitic larvae as an Edwardsiella member, but further comparable studies of E. lineata cnidomes are warranted for evaluating their taxonomic significance. [ABSTRACT FROM AUTHOR]

The family Eucodoniidae currently comprises five species in a single genus Eucodonium. Only one described species Eucodonium brownei has been reported in Japanese waters. We made detailed observations of the morphology of one of the species newly recorded in Japan: Eucodonium crassonemalis. This species possesses the following unique morphological characters: one to four medusa buds produced on stomach, marginal bulbs two, containing blackish or deep purple pigment granules, without apparent ocelli, tentacles two, with 10-20 yellow ring cnidocysts. [ABSTRACT FROM AUTHOR]

Organisms escape consumers using a variety of behaviors and structural or physiological defenses (e.g., toxins and irritants). Portuguese men o’ war (Physalia physalis) rely on nematocysts to immobilize or kill their prey, chiefly fish, but the nematocysts can also be painful or deadly to predators. Consequently, few species are known to approach, let alone consume, P. physalis. During an opportunistic birding excursion in coastal Texas, ~5 Ring-billed Gulls (Larus delawarensis) were observed picking up beached P. physalis, taking them to the water’s edge, and thrashing them in the water briefly before consuming them, or at least parts of them. These are among a very limited number of records of birds consuming P. physalis.

Members of the family Haloclavidae, belonging to the order Actiniaria, are characterized by the presence of a large siphonoglyph next to their actinopharynx and an aboral end without a basal disc. Members of the genus Haloclava Verrill, 1899 have been reported primarily from Europe and America, and have not yet been described from Japanese waters based on the collected specimen. In this study, I describe a new species, Haloclava hercules sp. nov., from the Pacific coast of Japan. This new species is chiefly characterized by cudgel-like blunt massive tentacles with knob-like acrospheres in the outer tentacular cycle and gigantic basitrichs over 250 µm in length, which are the largest known from sea anemones. [ABSTRACT FROM AUTHOR]

Background: One of the most charismatic, and yet not completely resolved example of mutualistic interaction is the partnership of clownfish and its symbiotic sea anemone. The mechanism explaining this tolerance currently relies on the molecular mimicry of clownfish epithelial mucus, which could serve as camouflage, preventing the anemone's nematocysts' discharge. Resident bacteria are known as key drivers of epithelial mucus chemical signature in vertebrates. A recent study has proposed a restructuration of the skin microbiota in a generalist clown fish when first contacting its symbiotic anemone. We explored a novel hypothesis by testing the effect of remote interaction on epithelial microbiota restructuration in both partners. Methods: With metataxonomics, we investigated the epithelial microbiota dynamic of 18 pairs of percula clownfish (Amphiprion percula) and their symbiotic anemone Heteractis magnifica in remote interaction, physical interaction and control groups for both partners during a 4-week trial. Results: The Physical and Remote Interaction groups' results evidence gradual epithelial microbiota convergence between both partners when fish and anemone were placed in the same water system. This convergence occurred preceding any physical contact between partners, and was maintained during the 2-week interaction period in both contact groups. After the interaction period, community structure of both fish and anemone's epthelial community structures maintained the interaction signature 2 weeks after fish–anemone pairs' separation. Furthermore, the interaction signature persistence was observed both in the Physical and Remote Interaction groups, thus suggesting that water-mediated chemical communication between symbiotic partners was strong enough to shift the skin microbiota durably, even after the separation of fish–anemone pairs. Finally, our results suggest that fish–anemone convergent microbiota restructuration was increasingly associated with the parallel recruitment of three Flavobacteriaceae strains closely related to a tyrosinase-producing Cellulophaga tyrosinoxydans. Conclusions: Our study shows that bacterial community restructuration, in the acclimation process, does not only rely on direct physical contact. Furthermore, our results challenge, for the first time, the traditional unidirectional chemical camouflage hypothesis, as we argue that convergence of the epithelial microbiota of both partners may play essential roles in establishing mutual acceptance. 9p4RZDq8XFt4wx9Qb_GP5v Video abstract Fish−anemone symbiotic relationship. [ABSTRACT FROM AUTHOR]

Some species of Cnidarians, well known venomous organisms, are able to induce serious health problems as well as economic and social trouble. A lot of data show that cnidarian venoms can be cytotoxic to cultured cells. Therefore, a priority of the research is to find tools which could counteract the damaging activity of venoms. In this connection, the modulatory effects exerted by extracts of plants Ananas comosus (L.) and Carica papaya (L.) on cytotoxicity of heterotrichous microbasic eurytele nematocysts isolated from the jellyfish Pelagia noctiluca was evaluated. The nematocyst extract induced strong cytotoxicity at highest tested doses with reduction of cell survival below 40% and IC50 value of 40×103 nematocysts/mL. Both plant extracts significantly improved the survival of cells, so that the IC50 resulted 74×103 and 100×103 nematocysts/mL in the presence of A. comosus and C. papaya extracts, respectively, both used at 10 and 100 μg/mL. Taking into account that heterotrichous microbasic eurytele nematocysts are present mainly in tentacles, which Pelagia noctiluca utilizes both for predation and defence, this result is particularly interesting from both ecological and sanitary point of view and demonstrates the potential of these plants extracts against cnidarian venoms.

Predator specialization has often been considered an evolutionary "dead end" due to the constraints associated with the evolution of morphological and functional optimizations throughout the organism. However, in some predators, these changes are localized in separate structures dedicated to prey capture. One of the most extreme cases of this modularity can be observed in siphonophores, a clade of pelagic colonial cnidarians that use tentilla (tentacle side branches armedwith nematocysts) exclusively for prey capture. Herewe study how siphonophore specialists and generalists evolve, and what morphological changes are associated with these transitions. To answer these questions, we: a) Measured 29 morphological characters of tentacles from 45 siphonophore species, b) mapped these data to a phylogenetic tree, and c) analyzed the evolutionary associations between morphological characters and prey-type data from the literature. Instead of a dead end, we found that siphonophore specialists can evolve into generalists, and that specialists on one prey type have directly evolved into specialists on other prey types. Our results show that siphonophore tentillum morphology has strong evolutionary associations with prey type, and suggest that shifts between prey types are linked to shifts in the morphology, mode of evolution, and evolutionary correlations of tentilla and their nematocysts. The evolutionary history of siphonophore specialization helps build a broader perspective on predatory niche diversification via morphological innovation and evolution. These findings contribute to understanding how specialization and morphological evolution have shaped present-day food webs. [ABSTRACT FROM AUTHOR]

Nematocysts are secretory organelles in cnidarians that play important roles in predation, defense, locomotion, and host invasion. However, the extent to which nematocysts contribute to adaptation and the mechanisms underlying nematocyst evolution are unclear. Here, we investigated the role of the nematocyst in cnidarian evolution based on eight nematocyst proteomes and 110 cnidarian transcriptomes/genomes. We detected extensive species-specific adaptive mutations in nematocyst proteins (NEMs) and evidence for decentralized evolution, in which most evolutionary events involved non-core NEMs, reflecting the rapid diversification of NEMs in cnidarians. Moreover, there was a 33–55 million year macroevolutionary lag between nematocyst evolution and the main phases of cnidarian diversification, suggesting that the nematocyst can act as a driving force in evolution. Quantitative analysis revealed an excess of adaptive changes in NEMs and enrichment for positively selected conserved NEMs. Together, these findings suggest that nematocysts may be key to the adaptive success of cnidarians and provide a reference for quantitative analyses of the roles of phenotypic novelties in adaptation.

A new species of box jellyfish, Carybdea wayamba sp. nov. is described here based on forty specimens collected from the south and northeast coasts of Sri Lanka, with the type location being Bonavista Reef, Galle Bay. This species is classified in the genus Carybdea due to the possession of a typical heart-shaped rhopaliar niche ostia with only one upper scale and epaulette-shaped gastric phacellae in the four corners of the stomach. This new species can be distinguished from other valid members of the genus Carybdea by the combination of the structure of the two velarial canal roots per octant with one broadly bi-forked velarial canal with narrow, lateral lobations on each root, and other morphological characters such as having typical knee-shaped pedalial canal bends without any appendages, and epaulette-shaped gastric phacellae with single-rooted, brush-shaped, multiple (three to five) short-stemmed, dendritically branched (both short and long branches) gastric filaments. This is the first novel cubomedusa described from Sri Lankan waters; and the first Carybdea species described with material from the North Indian Ocean. [ABSTRACT FROM AUTHOR]

Some species of Cnidarians, well known venomous organisms, are able to induce serious health problems as well as economic and social trouble. A lot of data show that cnidarian venoms can be cytotoxic to cultured cells. Therefore, a priority of the research is to find tools which could counteract the damaging activity of venoms. In this connection, the modulatory effects exerted by extracts of plants Ananas comosus (L.) and Carica papaya (L.) on cytotoxicity of heterotrichous microbasic eurytele nematocysts isolated from the jellyfish Pelagia noctiluca was evaluated. The nematocyst extract induced strong cytotoxicity at highest tested doses with reduction of cell survival below 40% and IC50 value of 40×103 nematocysts/mL. Both plant extracts significantly improved the survival of cells, so that the IC50 resulted 74×103 and 100×103 nematocysts/mL in the presence of A. comosus and C. papaya extracts, respectively, both used at 10 and 100 μg/mL. Taking into account that heterotrichous microbasic eurytele nematocysts are present mainly in tentacles, which Pelagia noctiluca utilizes both for predation and defence, this result is particularly interesting from both ecological and sanitary point of view and demonstrates the potential of these plants extracts against cnidarian venoms. [ABSTRACT FROM AUTHOR]

Cnidaria is the sister taxon to bilaterian animals, and therefore, represents a key reference lineage to understand early origins and evolution of the neural systems. The hydromedusa Aglantha digitale is arguably the best electrophysiologically studied jellyfish because of its system of giant axons and unique fast swimming/escape behaviors. Here, using a combination of scanning electron microscopy and immunohistochemistry together with phalloidin labeling, we systematically characterize both neural and muscular systems in Aglantha, summarizing and expanding further the previous knowledge on the microscopic neuroanatomy of this crucial reference species. We found that the majority, if not all (~2,500) neurons, that are labeled by FMRFamide antibody are different from those revealed by anti‐α‐tubulin immunostaining, making these two neuronal markers complementary to each other and, therefore, expanding the diversity of neural elements in Aglantha with two distinct neural subsystems. Our data uncovered the complex organization of neural networks forming a functional "annulus‐type" central nervous system with three subsets of giant axons, dozen subtypes of neurons, muscles, and a variety of receptors fully integrated with epithelial conductive pathways supporting swimming, escape and feeding behaviors. The observed unique adaptations within the Aglantha lineage (including giant axons innervating striated muscles) strongly support an extensive and wide‐spread parallel evolution of integrative and effector systems across Metazoa. [ABSTRACT FROM AUTHOR]

Natural substances produced by venomous marine organisms are thought to be possible sources of useful compounds and new drugs having the potential to open new ways for pharmacology, nutrition and environmental applications. In this framework, cnidarians are very interesting being widely distributed and all are venomous organisms; so, a deep knowledge of their occurrence, morphology of venomous structures and of effects of venoms at cellular level is fundamental to evaluate the possible utilization of venomous compounds or extracts. In this research, the morphology and occurrence of nematocysts in two cnidarian species (Aurelia aurita , Velella velella), and the preliminary evaluation of the cytotoxicity of V. velella crude extract, of which cytotoxicity on cell cultures at present is unknown, were considered. The specimens were sampled in Güllük Bay, Southwestern coast of Turkey, and in the Gulf of Genova, Northwestern coast of Italy. Six nematocyst types (a-isorhiza, A-isorhiza, O-isorhiza, eurytele, polyspiras, birhopaloid) having different sizes, were observed in A. aurita , and two types (eurytele and stenotele) in V. velella. The crude extract from V. velella showed cytotoxic activity against cultured fibroblasts L929 at high doses, while inducing cell proliferation at low doses. The protein content in the extract increased remarkably after disruption of nematocysts. Image 1098 • The shape of some nematocyst types differs in A. aurita sampled in different zones. • Nematocyst number-bell diameter relationship was not observed in A. aurita. • Only eurytele and stenotele nematocyst types were observed in V. velella. • High doses of V. velella crude venom caused decrease of survival in L929 cells. • Low doses of V. velella crude venom had positive effects on L929 cells. [ABSTRACT FROM AUTHOR]

Nematocysts, the stinging organelles of cnidarians, have remarkable mechanical properties. Hydra nematocyst capsules undergo volume changes of 50% during their explosive exocytosis and withstand osmotic pressures of beyond 100 bar. Recently, two novel protein components building up the nematocyst capsule wall in Hydra were identified. The cnidarian proline-rich protein 1 (CPP-1) characterized by a "rigid" polyproline motif and the elastic Cnidoin possessing a silk-like domain were shown to be part of the capsule structure via short cysteine-rich domains that spontaneously crosslink the proteins via disulfide bonds. In this study, recombinant Cnidoin and CPP-1 are expressed in E. coli and the elastic modulus of spontaneously crosslinked bulk proteins is compared with that of isolated nematocysts. For the fabrication of uniform protein nanofibers by electrospinning, the preparative conditions are systematically optimized. Both fibers remain stable even after rigorous washing and immersion into bulk water owing to the simultaneous crosslinking of cysteine-rich domains. This makes our nanofibers clearly different from other protein nanofibers that are not stable without chemical crosslinkers. Following the quantitative assessment of mechanical properties, the potential of Cnidoin and CPP-1 nanofibers is examined towards the maintenance of human mesenchymal stem cells. [ABSTRACT FROM AUTHOR]

Olindias muelleri is a hydromedusa distributed in the Mediterranean Sea and tropical Atlantic Ocean. Although this species is frequently reported in the Mediterranean Sea and its sting can cause serious human health problems, no data are currently available on its nematocysts. Therefore, the aim of the present investigation is to provide the description of its cnidome. Three types of nematocysts (microbasic b-mastigophores, pseudostenoteles and microbasic euryteles) and two unidentified types were identified in O. muelleri hydromedusa. For each nematocysts type, the location and abundance were recorded from tentacles, bell margin and manubrium. The three types of nematocysts identified in O. muelleri match with the types observed in the Brazilian Olindias sambaquiensis, the only species of the same genus for which information about the cnidome is available. However, the two species are clearly distinguished in terms of nematocyst size and location. No nematocysts have been observed in the exumbrella and subumbrella of O. muelleri, indicating that only its tentacles, bell margin or manubrium are responsible of envenomation, while the contact with all structures of O. sambaquiensis could be stinging. In addition, the unidentified medium-size capsules represent a character exclusive of O. muelleri. [ABSTRACT FROM AUTHOR]

Marine sponges thrive in benthic environments despite intense spatial competition and predator pressure. The sessile filter-feeders usually compensate their lack of physical defense and behavioral escape by a high level of bioactivity. In the stinging black sponge (Haliclona cnidata sp. nov.), these chemical defense mechanisms are complemented by “cellular weapons”—functional nematocysts likely acquired from cnidarians (kleptocnidism). Whereas, kleptocnidism might be facilitated by a close contact with cnidarian donors, preliminary investigations suggest that the stinging black sponge sustains nematocysts even if kept apart from cnidarians. As the underlying mechanisms causing this phenomenon remain unknown, the development of its nematocysts was studied in both presence and absence of potential cnidarian donors. First, we compared inherent nematocysts of adult sponge individuals with foreign nematocysts of co-cultivated cnidarians to identify potential donors. Second, we experimentally assessed the donor-independent and donor-dependent development of inherent and foreign nematocysts within cultures of sponge cell aggregates (SCAs). The inherent nematocysts comprised two specific types that both differed from those of the eight co-cultivated cnidarians. Specifically, we showed that the number of sponge-inherent nematocysts increased in SCAs over time in the absence of potential donors. Numbers of supplied foreign nematocysts, however, did not increase in the SCAs. We conclude that the observed increase of inherent nematocysts is due to the maturation of nematocyst precursor cells. Given these findings, we here propose the precursor hypothesis of sponge kleptocnidism. Accordingly, nematocyst precursors or immature nematocyte-nematocyst complexes might be initially acquired by sponges through filtration, maintained in sponge tissues, and nurtured to fully functioning nematocyte-nematocyst complexes. The underlying evolutionary processes are likely facilitated by bacteria-derived secondary metabolites and photosynthetically active dinoflagellates. Due to a simple body plan and the in vitro proliferation capacity of sponge cells, H. cnidata sp. nov. may serve as a novel evolutionary model system to further assess fundamental research questions regarding kleptocnidism. This study not only sheds new light on kleptocnidism in sponges, it also calls for a holobiontic view at defense mechanisms that involves the actual sponge, cnidarian nematocysts, dinoflagellate endosymbionts, and a complex microbial community.Life Science Identifier (LSID): urn:lsid:zoobank.org:act:509A075A-5D5D-417F-811E-52D3421D48BC

The substantial development of microscopic techniques and histological examination methods during the past five decades allowed for many new insights into the histology and microanatomy of Rhizostomeae. The present review focuses on new findings about histologically important structures: nerves, senses, muscles, gonads, zooxanthellae and nematocysts. Different ontogenetic stages of rhizostome species were included in the literature research, supplemented with the authors' unpublished data and figures. The overview of the research results reveals that the application of chemo- and immunohistochemical techniques have provided deeper insights into neuronal and sensory structures and their interconnections. Modern microscopic methods led to new findings on the histological gonadal organization and details of the processes of gametogenesis, fertilization, cleavage, gastrulation, and brooding. Advanced optical methods also allowed for a better understanding of Rhizostomeae-zooxanthellae associations and the morphology and function of nematocysts. Improvements in molecular biology allowed for more precise identification of zooxanthellae associated with rhizostome species. Although there has been significant progress in all of the research subjects covered here, we identify several knowledge gaps and conclude with some recommendations for future research., (Copyright © 2024. Published by Elsevier Ltd.)

Scientific knowledge and records on staurozoans are limited probably because of their inconspicuous life habit and the small number of specialists for this taxon. To increase the awareness for Staurozoa, we identified morphological and molecular features of the three staurozoan species Haliclystus tenuis Kishinouye, 1910, Haliclystus auricula Clark, 1863, and Craterolophus convolvulus (Johnston, 1835) collected on the coast of the island Helgoland to evaluate their suitability as diagnostic characters. Useful macromorphological diagnostic features were the patterns of white spots of nematocysts and internal arm structures, whereas tentacle and gonad follicle numbers showed high intraspecific variations. Morphometric measurements on photographs of living specimens provided reliable data for interspecific comparisons. Comprehensive nematocyst analyses revealed interspecific shape differences of isorhizas and three types of rhopaloids, indicating that the staurozoan cnidome is more diverse than previously assumed. However, the taxonomic value of nematocyst analyses in Staurozoa remains unclear because comprehensive data is still lacking for most species. Comparative molecular genetic sequence analyses of mitochondrial 16S and cytochrome c oxidase subunit I (COI) and nuclear 18S ribosomal DNA identified the three species and confirmed their morphological identification. In comparison to published data, our analyses indicate similarities between H. auricula and Haliclystus antarcticus Pfeffer, 1889. Proteomic fingerprinting by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) differentiated all three species, suggesting that this technique could provide an alternative rapid identification method for staurozoans. [ABSTRACT FROM AUTHOR]

Abstract Manual annotation and counting of entities in underwater photographs is common in many branches of marine biology. With a marked increase of jellyfish populations worldwide, understanding the dynamics of the polyp (scyphistoma) stage of their life-cycle is becoming increasingly important. In-situ studies of polyp population dynamics are scarce due to small size of the polyps and tedious manual work required to annotate and count large numbers of items in underwater photographs. We devised an experiment which shows a large variance between human annotators, as well as in annotations made by the same annotator. We have tackled this problem, which is present in many areas of marine biology, by developing a method for automated detection and counting. Our polyp counter (PoCo) uses a two-stage approach with a fast detector (Aggregated Channel Features) and a precise classifier consisting of a pre-trained Convolutional Neural Network and a Support Vector Machine. PoCo was tested on a year-long image dataset and performed with accuracy comparable to human annotators but with 70-fold reduction in time. The algorithm can be used in many marine biology applications, vastly reducing the amount of manual labor and enabling processing of much larger datasets. The source code is freely available on GitHub. Highlights • PoCo - computer-vision-based automated detection and counting algorithm. • Over 70× speedup over human annotator at comparable precision and recall. • Enables processing of large datasets and new possibilities in jellyfish research. [ABSTRACT FROM AUTHOR]

Certain species of sea anemone live in tightly packed communities, among clonemates and non-clonemates. Competition for space leads to intraspecific and interspecific aggressive interactions among anemones. The initial aggressive interactions appear to involve reciprocal discharge of cnidae triggered by contact with non-self feeding tentacles. We asked whether molecules contained in anemone-derived mucus constituted an important cue alone or in combination with cell surface molecules in stimulating aggressive or avoidance behaviors. In this study, we found that self and non-self stimuli differentially influenced two effector systems: cnida discharge and tentacle contraction. Interspecific mucus enhanced nematocyst discharge by 44% and spirocyst discharge by 90%, as compared to baseline discharge obtained in seawater alone. Conspecific stimuli accompanying touch inhibited specific tentacle contractions occurring on the far side of anemones relative to the site of contact. The greatest tentacle contractions occurred with exposure to interspecific mucus and tissue. Thus, several receptor systems are involved that integrate chemical and mechanical cues in order to initiate appropriate and graded effector responses during competition for space. [ABSTRACT FROM AUTHOR]

Background: Cnidocytes are specialized cells that define the phylum Cnidaria. They possess an "explosive" organelle called cnidocyst that is important for prey capture and anti-predator defense. An extraordinary morphological and functional complexity of the cnidocysts has inspired numerous studies to investigate their structure and development. However, the transcriptomes of the cells bearing these unique organelles are yet to be characterized, impeding our understanding of the genetic basis of their biogenesis. Results: In this study, we generated a nematocyte reporter transgenic line of the sea anemone Nematostella vectensis using the CRISPR/Cas9 system. By using a fluorescence-activated cell sorter (FACS), we have characterized cell type-specific transcriptomic profiles of various stages of cnidocyte maturation and showed that nematogenesis (the formation of functional cnidocysts) is underpinned by dramatic shifts in the spatiotemporal gene expression. Among the genes identified as upregulated in cnidocytes were Cnido-Jun and Cnido-Fos1—cnidarian-specific paralogs of the highly conserved c-Jun and c-Fos proteins of the stress-induced AP-1 transcriptional complex. The knockdown of the cnidocyte-specific c-Jun homolog by microinjection of morpholino antisense oligomer results in disruption of normal nematogenesis. Conclusions: Here, we show that the majority of upregulated genes and enriched biochemical pathways specific to cnidocytes are uncharacterized, emphasizing the need for further functional research on nematogenesis. The recruitment of the metazoan stress-related transcription factor c-Fos/c-Jun complex into nematogenesis highlights the evolutionary ingenuity and novelty associated with the formation of these highly complex, enigmatic, and phyletically unique organelles. Thus, we provide novel insights into the biology, development, and evolution of cnidocytes. [ABSTRACT FROM AUTHOR]

The sea anemone Condylactis gigantea is an ecologically important member of the benthic community in coral reefs of the tropical Atlantic, and displays two morphotypes with respect to the color in their tentacular tips: the green tip morphotype and the pink/purple tip morphotype. Although some molecular and ecological differences have been found between these morphotypes, no other morphological distinctions have been reported, and currently both are still considered a single taxonomic species. In the present study, we perform an exploration on the variability in the size of cnidae between these two morphotypes and performed statistical analyses to compare the 10 categories of cnidae from specimens hosted in the Cnidarian Collection of Gulf of Mexico and Mexican Caribbean, of the Universidad Nacional Autónoma de México, which were previously collected in several coral reefs localities of the Yucatán Peninsula. Results reveal no significant variation in cnidae size between the two morphotypes, but significant variations were found within each morphotype. In addition, we update the composition of the cnidom of C. gigantea, and the utility of the size of cnidae to distinguish between morphotypes or closely related species is discussed. [ABSTRACT FROM AUTHOR]

A new dinoflagellate, Paragymnodinium stigmaticum Yokouchi, Onuma & Horiguchi sp. nov., was described from sand samples collected at Sumiyoshi beach, Sado Island, Niigata Prefecture, Japan, based on observations at the light, scanning and transmission electron microscope levels together with molecular characterisation. The cells were 8.5–15.2 μm long and 6.3–12.4 μm wide. The episome and hyposome were subequal and hemispherical; although, the episome could also be conical. The cingulum was wide, well excavated and descended one quarter to a half of its own width. The sulcus was straight and widened slightly as it reached the antapex. A slightly curved sulcal extension-like furrow (SEF) ran from the right end of cingulum toward the apex. Cells possessed five to 10 yellowish brown chloroplasts, a red eyespot and small nematocysts. The dinoflagellate ingested prey cells despite the possession of chloroplasts, indicating a mixotrophic mode of nutrition. Paragymnodinium stigmaticum shared many morphological features and nutritional strategies with a known species of the genus Paragymnodinium, Paragymnodinium shiwhaense, including the possession of nematocysts, small polygonal amphiesmal vesicles and a mixotrophic mode of nutrition. However, it is clearly distinguished from P. shiwhaense by its feeding mechanism, its chloroplast ultrastructure, the presence of an eyespot, the absence of a plate-like structure in the amphiesmal vesicles and a benthic lifestyle (P. shiwhaense is planktonic). A phylogenetic analysis inferred from concatenated small and large subunit ribosomal DNA sequences recovered P. stigmaticum in a robust clade with P. shiwhaense that was included in the clade Gymnodinium sensu stricto. Therefore, it is reasonable to conclude that this dinoflagellate from Japan is a new species in the genus Paragymnodinium. [ABSTRACT FROM AUTHOR]

Nematocysts are characteristic organelles of the phylum cnidaria. They are designated kleptocnidae when sequestered in animals that feed on cnidaria. Kleptocnidae are known for more than a century. Nevertheless it is still enigmatic how selected nematocyst types survive in the predator and how they reach their final destination in the foreign body. In the free-living Platyhelminth Microstomum lineare the fate of nematocysts of the prey Hydra oligactis was analyzed at the ultrastructural level and by fluorescence microscopy using hydra polyps that had been stained in vivo with the fluorescent dyes TROMI and TRITC. M. lineare digested hydra tissue in its intestine within 30 min and all nematocyst types were phagocytosed without adherent cytoplasm by intestinal cnidophagocytes. Desmoneme and isorhiza nematocysts were digested whereas cnidophagocytes containing the venom-loaded stenotele nematocysts started to migrate out of the intestinal epithelia through the parenchyma to the epidermis thereby traversing the subintestinal and subepidermal muscle layer. Within one to two days, M. lineare began to form a muscle layer basolateral around epidermal cnidophagocytes. Epidermal stenoteles survived in M. lineare for at least four weeks. The ability of epidermal stenotele nematocysts to discharge suggest that this hydra organelle preserved its physiological properties in the new host. [ABSTRACT FROM AUTHOR]

Our team aimed to create a new, simple, and inexpensive technique for collecting and transferring of toxic jellyfish specimens and for nematocysts identification. We collected tentacles of Chironex spp., Morbakka spp., and Physalia spp., and transferred them from the beaches by standard and by 'vacuum sticky tape' (VST) techniques. For the VST technique, our team placed the sticky tape on a tentacle and then folded it over to seal the tentacle in the equivalent of a vacuum. We kept the VST in room temperature. For nematocyst identification, we placed the VST on a glass microscope slide and took photographs down the microscope's eye piece using a mobile phone camera. The image quality was as good as when produced by standard techniques. Different classes of toxic jellyfish could be identified. Thus, VST is a potential public health breakthrough because it is practical, durable, inexpensive, allows good discrimination. It enables early warning of danger to health and rapid response via social network. [ABSTRACT FROM AUTHOR]

Corallimorpharians are sessile cnidarians that are widely distributed from tropical to the polar region. Corallimorpharians exhibit a high level of intraspecific morphological variation and this causes problems in identification and uncertainty of the species boundary. Metarhodactis is a monotypic genus of the family Discosomidae and widely distributed in Thai waters. However there were a few studies on the detailed morpho-anatomical structure of Metarhodactis species in Thailand. This study aimed to examine the morphological and anatomical characteristic of Metarhodactis aff. boninensis, and to confirm the taxonomic status of this species. Our specimens collected from Prachuap Khiri Khan Province, Thailand, exhibited an oval-shaped oral disc with curled edge and produced only unbranched papilliform tentacles. Zooxanthellae densely inhabit in the tentacle gastrodermal tissue. M. aff. boninensis bears only one nematocyst in which six cnidae types were found. Holotrichs III and microbasic p-mastigophores were the most abundant cnidae, followed by holotrichs I. Male and female reproductive organs were observed in separate individuals. It was obvious that the M. aff. boninensis in this study was clearly distinct from the original description of M. boninensis from Japan on the basis of tentacle shape, cnidae type, and its locality. We suggest that further study to clarify the taxonomic position of M. aff. boninensis is required considering a combined data of morpho-anatomical characteristics and molecular markers. [ABSTRACT FROM AUTHOR]

Background: Pollution of marine ecosystems and, specifically, heavy metals contamination may compromise the physiology of marine animals with events occurring on a cellular and molecular level. The present study focuses on the effect of short-term exposure to heavy metals like Zinc, Cadmium, Cobalt and Lanthanum (2-10 mM) on the homeostasis of Pelagia noctiluca (Cnidaria, Scyphozoa), a jellyfish abundant in the Mediterranean sea. This species possesses stinging organoids, termed nematocysts, whose discharge and concomitant delivery of venom underlie the survival of all Cnidaria. Methods: Nematocysts discharge response, elicited by combined chemico-physical stimulation, was verified on excised oral arms exposed to heavy metals for 20 min. In addition, the hemolytic activity of toxins, contained in the crude venom extracted from nematocysts isolated from oral arms, was tested on human erythrocytes, in the presence of heavy metals or their mixture. Results: Treatment with heavy metals significantly inhibited both nematocysts discharge response and hemolytic activity of crude venom, in a dose-dependent manner, not involving oxidative events, that was irreversible in the case of Lanthanum. Conclusion: Our findings show that the homeostasis of Pelagia noctiluca, in terms of nematocysts discharge capability and effectiveness of venom toxins, is dramatically and rapidly compromised by heavy metals and confirm that this jellyfish is eligible as a model for ecotoxicological investigations.

Hydra, a fresh water Cnidarian, has been used as a model system to study regeneration and pattern formation. Here we report a newly identified hydra from Naukuchiatal, India. Comparison of Hydra vulgaris Naukuchiatal with Hydra magnipapillata, Hydra vulgaris AEP and Hydra vulgaris Ind-Pune showed variations in morphology. Nema arrangement in holotrichous isorhiza nematocytes showed transverse coiling pattern, a characteristic feature of the 'vulgaris' group. Phylogenetic analysis using conserved mitochondrial genes confirmed that Naukuchiatal hydra belongs to the 'vulgaris' group though it is a different strain particular to the type locality. Its morphological peculiarities could be the result of pristine environment. [ABSTRACT FROM AUTHOR]

Turritopsoides marhei, a new species of the hydrozoan family Oceaniidae, is described from the Maldives. This species can be distinguished from the only other member of the genus by the presence of more branched colonies, branches not being adnate to pedicels, longer pedicels, larger nematocysts, nematocyst-rich nematophore-like outgrowths from pedicels, smaller male gonophores, and a different geographic distribution. This finding represents the first record of the genus outside the type locality of its type species, in Belize. Molecular phylogenetic analyses show that, as expected, T. marhei belongs to the clade Filifera IV. However, the phylogenetic hypothesis based on both mitochondrial and nuclear DNA sequences reveals that most of the families of this group are polyphyletic, including Oceaniidae, and suggests that the morphological characters used to discriminate among filiferan families need to be revised thoroughly. [ABSTRACT FROM AUTHOR]

Cnidarians are probably the oldest group of animals to be venomous, yet our current picture of cnidarian venom evolution is highly imbalanced due to limited taxon sampling. High-throughput tandem mass spectrometry was used to determine venom composition of the scyphozoan Chrysaora lactea and two cubozoans Tamoya haplonema and Chiropsalmus quadrumanus . Protein recruitment patterns were then compared against 5 other cnidarian venom proteomes taken from the literature. A total of 28 putative toxin protein families were identified, many for the first time in Cnidaria. Character mapping analysis revealed that 17 toxin protein families with predominantly cytolytic biological activities were likely recruited into the cnidarian venom proteome before the lineage split between Anthozoa and Medusozoa. Thereafter, venoms of Medusozoa and Anthozoa differed during subsequent divergence of cnidarian classes. Recruitment and loss of toxin protein families did not correlate with accepted phylogenetic patterns of Cnidaria. Selective pressures that drive toxin diversification independent of taxonomic positioning have yet to be identified in Cnidaria and now warrant experimental consideration. [ABSTRACT FROM AUTHOR]