High densities of upside-down jellyfish (Cassiopea spp.) have been documented in anthropogenically disturbed coastal ecosystems including Jobos Bay, Puerto Rico. However, understanding their field ecology remains limited because most studies are laboratory-based, focusing on life history and symbiotic relationships. To investigate recruitment dynamics in field settings and improve ecological studies of this model system, we developed and preliminarily tested three original settlement trap designs to facilitate Cassiopea polyp collection under field conditions. Trap designs 1 and 2 contained only degraded Rhizophora mangle (red mangrove) leaves; trap design 3 included R. mangle leaves, Sargassum fluitans, and Halophila stipulacea; and a control design was void of substrate. Therefore, substrate type was not tested across all trap designs, and comparisons among designs are interpreted primarily in relation to trap structure rather than substrate identity. After 5 weeks, 25 polyps were found in Trap 3, exclusively upon R. mangle leaves; no polyps were observed on substrates in Traps 1 or 2, or the control. These preliminary results suggest that Trap 3 is most suitable for recruiting Cassiopea polyps and the preference for degraded R. mangle leaves is consistent with laboratory studies that show favorable conditions for polyp settlement. Biofilm was observed post hoc on the decomposed leaf in Trap 3 bearing 96% of the recruited polyps which warrants further investigation. The unique Cassiopea polyp settlement traps tested herein offer the potential to investigate recruitment rates in situ amidst changing climate conditions, thereby improving our understanding of Cassiopea spp. population explosion and collapse.

Upside-down jellyfish of the genus Cassiopea are ecologically significant components of tropical and subtropical coastal ecosystems; however, their population dynamics in natural mangrove systems remains poorly characterized. This study provides the first seasonally explicit assessment of Cassiopea spp. population structure in a Caribbean mangrove environment (Bajos de Santa Ana, Havana, Cuba), revealing pronounced seasonal demographic restructuring. Quadrat-based surveys (n = 190 total quadrats) were conducted during dry (December) and rainy (July) seasons across two consecutive years (2023–2024). We quantified jellyfish density, bell diameter, benthic community composition, and physicochemical parameters. Satellite-derived environmental data (turbidity, precipitation, sea surface temperature) provided temporal context. We documented a marked seasonal shift in population structure: the most pronounced seasonal contrast occurred in 2023, when December populations showed 3.8-fold higher densities (35.64 ± 19.70 vs. 9.28 ± 5.17 ind. m⁻2), and 29

Strobilation links the benthic polyp stage of scyphozoans with the pelagic medusa phase and determines when juvenile medusae are released into the water column. Temperature is widely recognized as a major environmental cue for this transition, but comparisons among species remain difficult because both “temperature” and “strobilation” are often treated as single variables. Here, we tested whether separating different components of the thermal regime and of the strobilation process helps clarify species-specific responses. Polyps of Stomolophus sp. 2, Cephea cephea, and Aurelia coerulea were exposed to a standardized experimental framework including warming, cooling, constant temperature, and treatments combining warming and cooling, using species-specific absolute temperature ranges. Temperature regulated strobilation in all three species, but not through a single general pattern. Strobilation onset was associated mainly with warming in Stomolophus sp. 2 and C. cephea, whereas cooling was the clearest thermal condition associated with the onset in A. coerulea. After initiation, thermal effects were expressed through different response variables: strobilation duration and ephyra diameter in Stomolophus sp. 2, strobilation duration in A. coerulea, and repeated strobilation events and total ephyrae production in C. cephea. In Stomolophus sp. 2 and C. cephea, cooling after warming was also associated with interruption of ongoing strobilation. Our results support interpreting strobilation as a sequence of partially separable components, including opening, expression, and closure of a medusa-production window, rather than as a single integrated response. This framework helps reconcile apparent contradictions in the literature and provides a basis for more comparable studies on the environmental regulation of life-cycle transitions in Scyphozoa. Because strobilation connects benthic asexual persistence with pelagic medusa recruitment, identifying both inductive and inhibitory environmental cues may be essential to understand how selection shapes the timing and duration of medusa production.

Cassiopea spp. exhibit mixotrophy through photoautotrophic symbiosis with zooxanthellae and heterotrophic prey capture via venom. Despite this, venom composition data remain limited. We present a 406.6 Mbp draft genome for Cassiopea andromeda, annotated using transcriptomes from aposymbiotic tissues. This genome supported proteomic mapping of venom from nematocysts of C. andromeda and Cassiopea xamachana from pristine and polluted mangroves in Brazil and a pristine mangrove in the Florida Keys. MS/MS data revealed no qualitative interspecific differences in toxin homologs, which were predominantly haemostasis-disrupting, suggesting venom specialization. Toxin abundance and nematocyst counts were higher in specimens from pristine environments, despite similar nematocyst types and sizes across samples. Environmental condition, rather than species or location, influenced venom abundance. We propose that modulation of nematocyst density may serve as an unrecognized mechanism for venom metering in adult Cassiopea.

The genus Hydra (Cnidaria, Hydrozoa) comprises a group of aquatic organisms that inhabit freshwater bodies worldwide, except for Antarctica. Hydras are widely recognized for their significant regenerative capacity and simple body plan. Despite the importance of these organisms in freshwater environments and due to the abundance and diversity of freshwater bodies in the Brazilian territory, curiously, this genus and other freshwater cnidarians are understudied. To assess the diversity of hydra in Brazil, we collected specimens from eight freshwater bodies in the SE and S of the country and built a phylogeny using a COI marker and comparing the morphologies with endemic species. These analyzes have yielded encouraging results, mainly the discovery of the species Hydra sinensis originating in China, highlighting the need to expand studies in less explored areas to better understand the relationship between species represented in Brazil and those from other regions of the world. Molecular and phylogenetic inferences, as proxies for species identity are essential to advance our knowledge of the diversity and evolution of Hydra and its relationship with different freshwater ecosystems in Brazil.

This study was designed to investigate the impact of heat stress on the physiological changes and mortality rates of different life stages of the rhizostome jellyfish species Cassiopea xamachana, including planula larvae, scyphistomae (polyps), and medusae. Both larval and scyphistoma stages of C. xamachana are relatively tolerant to high temperatures, but both experience nearly 100% mortality at 36 °C. Increasing temperatures also induced stage-specific effects. Settlement rates of artificially induced larvae were near 100% at lower temperatures but decreased at 34–36 °C; larvae were dead at 36 °C. When scyphistomae of C. xamachana were subjected to a gradual increase in temperature from 28 to 38 °C, polyp size declined steadily in starved animals, with animals showing clear signs of temperature stress between 35 and 36 °C. Small medusae of C. xamachana pulsed more than larger medusae and tended to have peak pulse rates at higher temperatures (~35 °C) compared to larger medusae (~29–33 °C), though the latter was not significant. At a temperature of 39 °C, all the medusae exhibited signs of heat stress, including pulsing erratically (generally lower) rather than steady rhythmic pulsations, releasing copious amounts of mucus, and having withdrawn oral arms. Temperature data presented here, and in the literature, show that pulsing C. xamachana medusae exhibit a bell-shaped curve, with temperatures over 38 °C being detrimental and becoming lethal at 40 °C. Based on the findings of this study, it is proposed that the medusa stage of C. xamachana has a higher tolerance for elevated temperatures compared to both the larvae and the polyps. Predictions of global climate change indicate that populations of C. xamachana will likely face longer and hotter summer periods, leading to increased population sizes. However, higher temperatures pose a greater risk to the survival of the species as they increase mortality in the polyp and larval stages compared to the medusa stage.

Jellyfishes have ecological and societal value, but our understanding of taxonomic identity of many jellyfish species remains limited. Here, an approach integrating morphological and molecular (16S ribosomal RNA and cytochrome oxidase I) data enables taxonomic assessment of the blubber jellyfish found in the Philippines. In this study, we aimed to resolve doubt on the taxonomy of Acromitoides purpurus, a valid binomen at the time of our research. Our morphological findings confirm that this jellyfish belongs to the genus Catostylus, and is distinct from known species of the genus inhabiting the Western Pacific, such as Catostylus ouwensi, Catostylus townsendi, and Catostylus mosaicus. Detailed morphological and molecular analyses of the type specimens from the Philippines with the other Catostylus species revive the binomen Catostylus purpurus and invalidate A. purpurus. Genetic analysis also distinguishes this Philippine jellyfish from C. townsendi and C. mosaicus. Through this study, we arranged several Catostylidae taxa into species inquirendae (Catostylus tripterus, Catostylus turgescens, and Acromitoides stiphropterus) and one genus inquirenda (Acromitoides) and provided an identification key for species of Catostylus. This comprehensive study confirms the blubber jellyfish as C. purpurus, enriching our understanding of jellyfish biodiversity. The integration of morphological and genetic analyses proves vital in resolving taxonomic ambiguities within the Catostylidae family and in the accurate identification of scyphozoan jellyfishes.

The morphology of members of the order Rhizostomeae is revisited considering all life cycle stages, but with emphasis on the medusa. The current classification of the group is presented, and some aspects of species diversity are discussed. The main issues investigated since the 1970s are briefly presented by decade.

The limited temporal completeness and taxonomic accuracy of species lists, made available in a traditional manner in scientific publications, has always represented a problem. These lists are invariably limited to a few taxonomic groups and do not represent up-to-date knowledge of all species and classifications. In this context, the Brazilian megadiverse fauna is no exception, and the Catalogo Taxonomico da Fauna do Brasil (CTFB) (http://fauna.jbrj.gov.br/), made public in 2015, represents a database on biodiversity anchored on a list of valid and expertly recognized scientific names of animals in Brazil. The CTFB is updated in near real time by a team of more than 800 specialists. By January 1, 2024, the CTFB compiled 133,691 nominal species, with 125,138 that were considered valid. Most of the valid species were arthropods (82.3%, with more than 102,000 species) and chordates (7.69%, with over 11,000 species). These taxa were followed by a cluster composed of Mollusca (3,567 species), Platyhelminthes (2,292 species), Annelida (1,833 species), and Nematoda (1,447 species). All remaining groups had less than 1,000 species reported in Brazil, with Cnidaria (831 species), Porifera (628 species), Rotifera (606 species), and Bryozoa (520 species) representing those with more than 500 species. Analysis of the CTFB database can facilitate and direct efforts towards the discovery of new species in Brazil, but it is also fundamental in providing the best available list of valid nominal species to users, including those in science, health, conservation efforts, and any initiative involving animals. The importance of the CTFB is evidenced by the elevated number of citations in the scientific literature in diverse areas of biology, law, anthropology, education, forensic science, and veterinary science, among others.

Rhizostomeae research based on morphological approaches was reinforced and diversified by new techniques after the 1970s, including developing methodologies for phylogenetic analysis, the rise of the polymerase chain reaction, and the emergence of different sequencing technologies. Here, we summarize the contribution of morphological and molecular data to the study of the classification and phylogenetic relationships of Rhizostomeae in addition to the use of molecular data in studies at the population, species, and supraspecific levels. Throughout the history of the study of the Rhizostomeae systematics, morphological data have been neglected when it comes to phylogenetic inferences, which is reflected in the lack of a phylogenetic analysis of the taxa within Rhizostomeae based on phenotypic characters of the adult medusa. Concerning molecular data, ca. 3,200 nucleotide sequences are available in GenBank and are mainly used for discovering, delimiting, describing, and identifying species. Molecular approaches have also allowed species monitoring by qPCR and metabarcoding of environmental DNA, as well as unveiling the distribution and genetic diversity of jellyfish populations, shedding light on introduction events, conservation, and health of edible jellyfish stocks. Nucleotide sequences have also been key for the development of phylogenetic hypotheses that serve as basis for investigations on the origin and diversification of morphological, ecological, and behavioral traits within Cnidaria; however, despite the progress achieved, phylogenetic uncertainty still exists, especially within the formerly known superfamily Inscapulatae. Future directions in Rhizostomeae research involve generating molecular and morphological data of neglected taxa, which represents a golden opportunity to understand the evolution of Rhizostomeae.

Jellyfish consumption is popular in Asia but neglected in other continents, where their abundance could represent a sustainable food source. This study explored the potential of jellyfish as food in the Latin American population. Through an online survey that included questions about socio-demographics, personality traits, and acceptance of jellyfish as food, responses by 6,597 Latin Americans (55.9 % females; 18 - 90 years old) in nine countries (Argentina, Brazil, Chile, Colombia, Ecuador, El Salvador, Mexico, Peru, and Uruguay) were collected. Jellyfish consumption acceptance (JCA) was positively correlated with age, educational level, and income, and negatively correlated with food neophobia and sensitivity to disgust. Comparing the nine countries, significant differences were identified. The highest levels of JCA were found among Argentinians and Peruvians, while the lowest values were observed among Ecuadorians and Salvadorians. Based on the modality of consumption (visible appearance, ingredient role, cooking method, carrier flavour of the recipe), four groups of countries with similar acceptance were observed: 1) Peru, Argentina, Mexico, Colombia, and Brazil; 2) El Salvador; 3) Chile and Uruguay; and 4) Ecuador. Moreover, differences in food pairing choices were highlighted among countries of the Northern hemisphere (El Salvador, Mexico, and Colombia), middle latitude (Ecuador, Peru, and Brazil) and the southernmost (Uruguay, Argentina, and Chile). In conclusion, this research contributes to the understanding of jellyfish as a sustainable food source in Latin America and provides useful insights for future market development and the adoption of tailored approaches to maximise the use and consumption of jellyfish across the region.

Cilia are widely present in metazoans and have various sensory and motor functions, including collection of particles through feeding currents in suspensivorous animals. Suspended particles occur at low densities and are too small to be captured individually, and therefore must be concentrated. Animals that feed on these particles have developed different mechanisms to encounter and capture their food. These mechanisms occur in three phases: (i) encounter; (ii) capture; and (iii) particle handling, which occurs by means of a cilia-generated current or the movement of capturing structures (e.g. tentacles) that transport the particle to the mouth. Cilia may be involved in any of these phases. Some cnidarians, as do other suspensivorous animals, utilise cilia in their feeding mechanisms. However, few studies have considered ciliary flow when examining the biomechanics of cnidarian feeding. Anthozoans (sessile cnidarians) are known to possess flow-promoting cilia, but these are absent in medusae. The traditional view is that jellyfish capture prey only by means of nematocysts (stinging structures) and mucus, and do not possess cilia that collect suspended particles. Herein, we first provide an overview of suspension feeding in invertebrates, and then critically analyse the presence, distribution, and function of cilia in the Cnidaria (mainly Medusozoa), with a focus on particle collection (suspension feeding). We analyse the different mechanisms of suspension feeding and sort them according to our proposed classification framework. We present a scheme for the phases of pelagic jellyfish suspension feeding based on this classification. There is evidence that cilia create currents but act only in phases 1 and 3 of suspension feeding in medusozoans. Research suggests that some scyphomedusae must exploit other nutritional sources besides prey captured by nematocysts and mucus, since the resources provided by this diet alone are insufficient to meet their energy requirements. Therefore, smaller particles and prey may be captured through other phase-2 mechanisms that could involve ciliary currents. We hypothesise that medusae, besides capturing prey by nematocysts (present in the tentacles and oral arms), also capture small particles with their cilia, therefore expanding their trophic niche and suggesting reinterpretation of the trophic role of medusoid cnidarians as exclusively plankton predators. We suggest further study of particle collection by ciliary action and its influence on the biomechanics of jellyfishes, to expand our understanding of the ecology of this group.

Max Egon Thiel worked as curator of the aquatic invertebrates collection at the Zoological Museum in Hamburg until 1963. Specialising in marine planktonic megafauna, he compiled a broad review of the research history on the Scyphozoa (Coronatae, Cubomedusae, Semaeostomeae) including the Staurozoa (as Stauromedusae), written in German. After publishing major parts in 1936 and 1938, World War II delayed further chapters until 1959 and 1962. A complete bibliography covering references up to 1970 was not printed until 1977. The final section on the taxon Rhizostomeae was completed as a typescript before his death, but was never published. In the present paper, the authors provide a synopsis of the published volumes in English. Following Thiel's original outline, the research history, as well as reviews of the current knowledge at the time about morphology, histology, ontogeny (life cycle), physiology, ecology, and phylogeny of the taxa are presented. The paper is complemented by two electronic supplements: A translated and revised version of the left-behind typescript of Max Egon Thiel about the taxon Rhizostomeae, and the revised digital list of references published in Thiel (1977).

In the present study we reviewed the life cycles and reproduction strategies of the order Rhizostomeae. We found 28 species with described life cycles representing ∼30% of the valid species. The metagenetic life cycle of most scyphozoans, which includes the benthic asexually-reproducing polyp and the pelagic sexually-reproducing medusa, is exhibited by all rhizostome species. Rhizostomeae are dioecious with only two exceptions described as hermaphroditic. Sexual dimorphism can be found in species with special external structures utilised for brooding but others show no sexual dimorphism despite the colour of mature gonads. Six asexual reproduction modes have been described for the production of new polyps but rhizostome polyps propagate through a main mode that differs among taxa. Species belonging to Dactyliophorae produce new polyps by podocysts whereas the Kolpophorae new polyps develop from free-swimming buds. The number of ephyrae formed per strobila differs between taxa with monodisc and polydisc strobilation in the Kolpophorae and Dactyliophorae, respectively. Given the low number of studied species it is expectable that new reproductive strategies will be discovered when additional species are investigated. We recommend increasing (1) descriptions on life cycles and reproductive strategies for a greater number of species, (2) attempts to locate the polyps in the field, (3) the study of species in their natural environment, to understand the population dynamics of Rhizostomeae and to clarify the potential of artificial structures to increase medusa populations. In addition, experimental studies are needed to improve our understanding of the factors affecting transitions between life cycle stages and medusa production rates.

An undescribed species of ulmarid medusa was observed in situ and captured at 812 m depth within the Sumisu Caldera, Ogasawara Islands, Japan. Morphological and molecular evidence points to it being distinct from other ulmarid medusae and a new species (pagesi), genus (Santjordia) and subfamily (Santjordiinae) are herein erected to contain it. This new subfamily of semaeostome ulmarid medusae has both marginal and subumbrellar rhopalia, making it unique within the order Semaeostomeae. Although the combination of subumbrellar tentacles and the lack of branched canals should warrant the erection of a new family within the Semaeostomeae, a lack of information on the gonad structure and poor bootstrap support in the molecular phylogenetic tree cause us to relegate it to the catch-all family Ulmaridae, until greater taxon sampling and phylogenetic analyses are carried out for the Semaeostomeae.

Ephyrae, the early stages of scyphozoan jellyfish, possess a conserved morphology among species. However, ontogenetic transitions lead to morphologically different shapes among scyphozoan lineages, with important consequences for swimming biomechanics, bioenergetics and ecology. We used high-speed imaging to analyse biomechanical and kinematic variables of swimming in 17 species of Scyphozoa (1 Coronatae, 8 "Semaeostomeae" and 8 Rhizostomeae) at different developmental stages. Swimming kinematics of early ephyrae were similar, in general, but differences related to major lineages emerged through development. Rhizostomeae medusae have more prolate bells, shorter pulse cycles and higher swimming performances. Medusae of "Semaeostomeae", in turn, have more variable bell shapes and most species had lower swimming performances. Despite these differences, both groups travelled the same distance per pulse suggesting that each pulse is hydrodynamically similar. Therefore, higher swimming velocities are achieved in species with higher pulsation frequencies. Our results suggest that medusae of Rhizostomeae and "Semaeostomeae" have evolved bell kinematics with different optimized traits, rhizostomes optimize rapid fluid processing, through faster pulsations, while "semaeostomes" optimize swimming efficiency, through longer interpulse intervals that enhance mechanisms of passive energy recapture.

From the late 1890s to the mid-1900s, descriptions of Ceriantharia species based solely on analyses of the larval forms were a common practice. Such approaches resulted in taxonomic inconsistencies and an extensive number of species with unreviewed descriptions. The present study discusses the taxonomic position of individuals from the northern Amazon coast, Brazil, using morphological, molecular, and biogeographic data. DNA samples of three larvae were collected, the COI marker was amplified, and the sequences were analyzed and checked on the NCBI databases. The morphology of each larva collected was analyzed and compared with available data. Morphological, molecular, and biogeographical evidence led to identification of the larvae from Maiandeua Island (Pará) as Isarachnanthus nocturnus (den Hartog, 1977 ), which has a wide distribution along the Brazilian coast (from southern to northern Brazil) and the Caribbean Sea. The records also support the occurrence of the taxa in areas with estuarine influence. The larvae from Pará are morphologically similar to Ovactis brasiliensis van Beneden, 1897 . However, due to inconsistent description performed by van Beneden ( 1897 ), we suggest that O. brasiliensis be considered a species inquirenda .

Unveiling the tempo and mode of animal evolution is necessary to understand the links between environmental changes and biological innovation. Although the earliest unambiguous metazoan fossils date to the late Ediacaran period, molecular clock estimates agree that the last common ancestor (LCA) of all extant animals emerged ~850 Ma, in the Tonian period, before the oldest evidence for widespread ocean oxygenation at ~635-560 Ma in the Ediacaran period. Metazoans are aerobic organisms, that is, they are dependent on oxygen to survive. In low-oxygen conditions, most animals have an evolutionarily conserved pathway for maintaining oxygen homeostasis that triggers physiological changes in gene expression via the hypoxia-inducible factor (HIFa). However, here we confirm the absence of the characteristic HIFa protein domain responsible for the oxygen sensing of HIFa in sponges and ctenophores, indicating the LCA of metazoans lacked the functional protein domain as well, and so could have maintained their transcription levels unaltered under the very low-oxygen concentrations of their environments. Using Bayesian relaxed molecular clock dating, we inferred that the ancestral gene lineage responsible for HIFa arose in the Mesoproterozoic Era, ~1273 Ma (Credibility Interval 957-1621 Ma), consistent with the idea that important genetic machinery associated with animals evolved much earlier than the LCA of animals. Our data suggest at least two duplication events in the evolutionary history of HIFa, which generated three vertebrate paralogs, products of the two successive whole-genome duplications that occurred in the vertebrate LCA. Overall, our results support the hypothesis of a pre-Tonian emergence of metazoans under low-oxygen conditions, and an increase in oxygen response elements during animal evolution.

An extensive sample of well-preserved conulariids from the Pennsylvanian of the North American Midcontinent (Texas and Oklahoma, USA) have been studied using X-ray micro-Computed Tomography (µCT) and have shown structures identified as longitudinal muscle bundles and a potential gastric cavity. These unequivocal structures appear in several specimens coming from different sites. Their preservation varies from a gastric cavity with muscle bundles in some individuals to only longitudinal muscle bundles in others. The muscle bundles fuse apically or medially, normally forming V-shaped pairs, and they extend along the theca/exoskeleton, parallel to the corner, towards the aperture. Longitudinal bundles have predominant perradial positions. Although there have been some articles on conulariid soft parts, most of them refer to relic soft parts. This is the first time that these structures are shown using µCT. Discovery of conulariid soft parts contributes to knowledge of metazoan evolutionary history.