Programa LIFE Comisión Europea (LIFE NAT 080064 CUBOMED; Ministerio de Agricultura, Alimentación y Medio Ambiente; Fundación Biodiversidad; Dirección General del Agua, Generalitat Valenciana; Fundació Baleària; El Portet de Denia.

Made available in DSpace on 2014-06-12T15:07:27Z (GMT). No. of bitstreams: 2 arquivo5620_1.pdf: 8916043 bytes, checksum: 669ed68c15dd8910790b9473691f2d57 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2010 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Na ausência de um sistema imune adaptativo propriamente dito, os cnidários se valem de uma série de mecanismos bioquímicos e celulares que coletivamente compreendem sistemas da imunidade inata e são utilizados para o reconhecimento de micro-organismos, tanto parasitas quanto simbiontes. O objetivo do presente trabalho foi investigar se precursores gênicos relacionados a três polipeptídios envolvidos na resposta inata (CTL: lectina do tipo C, MBL: lectina ligante de manose e C3: componente 3 do sistema complemento) seriam expressos em Palythoa caribaeorum. Tendo como base dados moleculares descritos na literatura para os cnidários Nematostella vectensis, Pocillopora damicornis, Acropora millepora e Swiftia exserta, foram utilizadas duas estratégias metodológicas distintas para responder tal proposição: (1) síntese direta de cDNA a partir do RNAm e amplificação dos homólogos por RT-PCR e (2) construção de uma biblioteca de cDNA para propagação e resgate dos precursores completos (full length cDNAs). Ao todo, foram obtidos 11 produtos de RT-PCR (cDNAs amplificados), dos quais um se refere a um segmento similar a um domínio do receptor de imunoglobulinas das células NK (KIR), encontrado em gorilas. A presença de um domínio semelhante a KIR em P. caribaeorum sugeriria a existência de formas alternativas de imunidade antecipatória em cnidários. Tão importante quanto esse achado foi a obtenção de amplicons de CTL. Dessa forma, os níveis de expressão de transcritos de CTL foram comparados entre colônias sadias e doentes (em processo de branqueamento) de P. caribaeorum. Os resultados para o ensaio de expressão diferencial mostraram que a CTL teve uma expressão aumentada entre 63,2 e 65,5% nas colônias branqueadas, o que sugere um possível papel na resposta ao branqueamento, uma vez que essas moléculas participam do processo de reconhecimento celular. Esse resultado pode ser interpretado de duas formas: o aumento na transcrição de CTL após o branqueamento seria uma tentativa de proteção imediata contra patógenos ou estaria envolvido no recrutamento de novos simbiontes. Como um todo, o estudo de moléculas polipeptídicas da imunidade de cnidários é de importância considerável. Não somente fornece dados sobre a ancestralidade e evolução das reações imunes, mas também serve de base para uma série de aplicações de caráter científico e biotecnológico, que vão desde o monitoramento e conservação de espécies marinhas até estudos voltados ao tratamento e cura de doenças que acometem vertebrados superiores

La présence d’un récepteur de type RXR a récemment été rapporté chez la pensée de mer, Renilla koellikeri, de même que chez d’autres anthozoaires, et le NO semble jouer des différents rôles physiologiques, chez plusieurs cnidaires. L’acide rétinoïque (AR) et le monoxyde d’azote (NO) sont connus pour leur implication dans l’induction de la croissance des neurites chez les vertébrés ainsi que chez les invertébrés. Mais jusqu’à présent, aucun rôle de ces agents n’a encore été identifié chez ce phylum ancien des invertébrés. Dans le but de montrer que ces agents morphogénétiques ont un rôle dans le développement neuronal chez ces ancêtres des métazoaires bilatéraux, nous avons utilisé des cultures primaires de cellules du cnidaire anthozoaire Renilla koellikeri (pensée de mer), doté d’un système nerveux des plus primitif. Nous avons trouvé que les deux types d’acide rétinoïque, 9-cis et 11-trans, induisent une prolifération cellulaire dose-dépendante en fonction du temps dans les boîtes de pétri enduites de polylysine. Les cultures cellulaires exposées à l’acide rétinoïque dans les boîtes sans polylysine montrent une différenciation en des cellules épithéliales. D’autre part, le NO induit exclusivement une différenciation neuronale dans les boîtes enduites de polylysine. Aucun autre type de cellules subit un différenciation en présence de NO et la densité des cellules dédifférenciées a diminué. Les prolongements des neurones différenciés semblent s’enchevêtrer et former un réseau neuronal assez dense. L’ensemble de ces observations suggère que l’acide rétinoïque, contrairement à NO, est associé à l’activité mitotique, et que l’acide rétinoïque et le NO sont impliqués différemment dans la spécification cellulaire, respectivement épithéliale et neuronale, chez la pensée de mer. Le type d’action déclenchée, qu’il soit la mitogénèse ou la différenciation (épithéliale ou neuronale), varie alors selon l’état d’adhésion des cellules au substrat. Comme les données moléculaires et paléontologiques rapprochent les cnidaires, telle la pensée de mer, des ancêtres des eumétazoaires, nos résultats suggèrent que le rôle morphogénétique de l’acide rétinoïque et du NO est enraciné dans l’ancêtre commun de tous les métazoaires. / Retinoic acid receptors were recently reported in the sea pansy, Renilla koellikeri, and in other anthozoans, and NO seems to play various roles in several cnidarians. Retinoic acid (RA) and nitric oxide (NO) are known for their implication in inducing neurite outgrowth in both vertebrates and invertebrates. But so far, no role of these agents has been identified in this basal metazoan phylum. In order to show that these agents have a morphogenetic role in neuronal development in the ancestors of bilateral metazoan. We used primary cultures of cells from the cnidarian anthozoan Renilla koellikeri (sea pansy), with the most primary nervous system. We found that both 9-cis and 11-trans retinoic acid induced cell proliferation in dose- and time-dependant manners in petri dishes coated with polylysine. Cell cultures exposed to retinoic acid in dishes devoid of polylysine were observed to differentiate into epithelial cells. On the other hand, NO induced extensive neurite outgrowth in polylysine-coated culture dishes. No other celle type underwent differentiation in the presence of NO, and the density of dedifferentiated cells was reduced. The neurites of the differentiating neurons appeared to intertwine and form a loose nerve net. These observations suggest that retinoic acid, but not NO, has mitogenic activity, and that retinoic acid and NO are differentially involved in nerve cell specification in the sea pansy. The type of action, mitogenesis or cell differenciation (epithelial or neural), depends on the degree of cell adhesion to substrate. As both molecular and paleontological evidence place cnidarians such as the sea pansy closest to the eumetazoan ancestor, our results suggest that the morphogenetic role of retinoic acid and NO was rooted in the commun ancestor of all metazoans.

Os ciclos de vida de Clytia linearis (Thornely, 1899) e de duas espécies apresentando caracteres considerados diagnósticos de Clytia gracilis (M. Sars, 1850) – aqui denominadas Clytia cf. gracilis sp. 1 e Clytia cf. gracilis sp. 2 – foram estudados com base em espécimes coletados no infralitoral raso da costa de São Sebastião e Ilhabela, sudeste do Brasil, entre fevereiro de 1999 e abril de 2000. Medusas foram cultivadas em laboratório, a temperatura de 22-24oC. Colônias de C. linearis são monossifônicas, simpodiais, com até 21,5mm de altura e portando até 26 hidrantes e 10 gonângios. Medusas adultas, alcançando 2,5-3,6mm de diâmetro e até 29 tentáculos e 28 estatocistos, podem ser distinguidas de outras espécies de Clytia pela presença de nematocistos microbásicos mastigóforos do tipo C. Medusas adultas de Clytia cf. gracilis spp. 1 e 2 podem ser distinguidas das demais espécies do gênero estudadas até o momento pela presença de uma fileira de nematocistos microbásicos mastigóforos do tipo A na umbrela, no nível do canal circular. Medusas adultas de C. cf. gracilis sp. 1 e C. cf. gracilis sp. 2 apresentam até 16 tentáculos e podem ser distinguidas entre si pelo diâmetro da umbrela: 6,6-10,1mm e 3,6-5,5mm, respectivamente. Quanto ao estágio de pólipo, C. cf. gracilis sp. 1 apresenta usualmente colônias dicotômicas eretas, hidrotecas alongadas, e gonotecas na hidrorriza e pedículos. Estes caracteres concordam com a descrição de C. gracilis, mas as espécies diferem entre si pela morfometria das gonotecas e dos nematocistos microbásicos mastigóforos do tipo B: aproximadamente 15mm de comprimento para C. gracilis e 9-10mm para C. cf. gracilis sp. 1. Por outro lado, nematocistos do tipo B de C. cf. gracilis sp. 2, com aproximadamente 14,5mm de comprimento, em média, são morfometricamente semelhantes aos de C. gracilis. No entanto, C. cf. gracilis sp. 2 difere de C. gracilis pela forma da hidroteca, por apresentar gonotecas apenas na hidrorriza, e pelo hábito polissifônico do colônias bem desenvolvidas. Uma terceira espécie, C. cf. gracilis sp. 3, é descrita com base em uma colônia sem gonângios. Aspectos da sistemática de Clytia são discutidos. / he life-cycles of Clytia linearis (Thornely, 1899) and two species with characters considered diagnostic of Clytia gracilis (M. Sars, 1850) – Clytia cf. gracilis sp. 1 and Clytia cf. gracilis sp. 2 – have been studied based on specimens collected in the shallow subtidal coast of São Sebastião and Ilhabela, southeast Brazil, between February 1999 and April 2000. Medusae were cultured in the laboratory (22-24oC). Colonies of C. linearis are monosiphonic, sympodial, up to 21.5mm high and bearing up to 26 hydranths and 10 gonangia. Adult medusae reached 2.5-3.6mm in diameter, and up to 29 tentacles and 28 statocysts. The presence of microbasic mastigophore type C nematocysts distinguishes adult medusae of C. linearis from other species of Clytia. A band of microbasic mastigophore type A nematocysts in the umbrella, at the level of the circular canal, distinguishes adult medusae of Clytia cf. gracilis spp. 1 and 2 from other species of the genus. Adult medusae of C. cf. gracilis sp. 1 and C. cf. gracilis sp. 2 have up to 16 tentacles, and can be distinguished by the diameter of the umbrella: 6.6-10.1mm and 3.6-5.5mm, respectively. Colonies of C. cf. gracilis sp. 1 are usually erect and dichotomous, the hydrothecae are elongated and the gonothecae present in the hydrorhiza and pedicels. These features closely match with the description of C. gracilis, but both species differ in the morphometry of the gonothecae and microbasic mastigophore type B nematocysts: about 15mm (length) for C. gracilis and 9-10mm for C. cf. gracilis sp. 1. Type B nematocysts of C. cf. gracilis sp. 2 (about 14.5mm in length) are more similar in size to those of C. gracilis. However, the former species differs from the latter in the shape of the hydrothecae, by having gonothecae only at the hydrorhiza and polysiphonic well-developed colonies. A third species, C. cf. gracilis sp. 3, is described based on an unfertile colony. Aspects of the systematics of Clytia are discussed.

Nausithoe aurea Silveira & Morandini, 1997 é uma espécie metagenética e dióica com fecundação externa. Os oócitos são liberados continuamente (55 dias em laboratório), porém com grandes variações no número a cada dia. No desenvolvimento embrionário a clivagem, após o estágio de 8 células, passa de holoblástica e igual para pseudoespiral. A gastrulação ocorre por ingressão multipolar e inicia-se aproximadamente 24 horas após a fecundação. A estrutura histológica geral das gônadas assemelha-se a outros Scyphozoa, onde os gonócitos proliferam a partir da gastroderme, migram e diferenciam-se na mesogléia. Na gônada masculina as células germinativas formam camadas razoavelmente distintas e constituem folículos testiculares. Na gônada feminina os oócitos surgem da zona germinativa na gastroderme e apresentam um gradiente de maturação a partir deste ponto (cortes no sentido oral-aboral). Os oócitos encontram-se livres na mesogléia da gônada, sem associação com outras células. A relação espacial entre a musculatura circular, as gônadas e o sulco coronal, é uma característica a ser usada na sistemática do gênero Nausithoe Kölliker, 1853. / Nausithoe aurea Silveira & Morandini, 1997 is a metagenetic and dioecious species with external fertilization. The oocytes are released continuously (55 days in laboratory), but with great variations in the daily number. In the embryonic development the cleavage, after the 8 cells stage, changes from holoblastic and adequal to pseudospiral. The gastrulation occurs through multipolar ingression and begin 24 hours after fertilization. The general histological structure of the gonads resembles other Scyphozoa, in which the gonocytes proliferate from the gastrodermis, migrate and differentiate in the mesoglea. In the male gonad the germ cells are arranged in distinctive layers and form follicles (cysts). In the female gonad the oocytes develop from the germinative zone in the gastrodermis and present a maturing gradient from this point on (oral-aboral sections). The oocytes are free in the gonad mesoglea, without association to any cell. The spatial relation of the coronal musculature, gonads and coronal groove, is a character to be used in the systematics of the genus Nausithoe Kölliker, 1853.

Individuals of the cnidarian genus Physalia are a common sight at New Zealand beaches and are the primary cause of jellyfish stings to beachgoers each year. The identity of the species and the environmental factors that determine its presence are unknown. Lack of knowledge of many marine species is not unusual, as pelagic invertebrates often lack detailed taxonomic descriptions as well as information about their dispersal mechanisms such that meaningful patterns of distribution and dispersal are almost impossible to determine. Molecular systematics has proven to be a powerful tool for species identification and for determining geographical distributions. However, other techniques are needed to indicate the causal mechanisms that may result in a particular species distribution. The aim of this study was to apply molecular techniques to the cnidarian genus Physalia to establish which species occur in coastal New Zealand, and to apply models to attempt to forecast its occurrence and infer some mechanisms of dispersal. Physalia specimens were collected from New Zealand, Australia and Hawaii and sequenced for Cytochrome c oxidase I (COI) and the Internal transcribed spacer 1 (ITS1). Three clans were found: a Pacific-wide clan, an Australasian clan and New Zealand endemic clan with a distribution confined to the Bay of Plenty and the East Coast of the North Island. Forecasting Physalia occurrence directly from presence data using artificial neural networks (ANN) proved unsuccessful and it was necessary to pre-process the presence data using a variable sliding window to reduce noise and improve accuracy. This modelling approach outperformed the time lagged based networks giving improved forecasts in both regions that were assessed. The ANN models were able to indicated significant trends in the data but would require more data at higher resolution to give more accurate forecasts of Physalia occurrence suitable for decision making on New Zealand beaches. To determine possible causal mechanisms of recorded occurrences and to identify possible origins of Physalia the presence and absence of Physalia on swimming beaches throughout the summer season was modelled using ANN and Naϊve Bayesian Classifier (NBC). Both models were trained on the same data consisting of oceanographic variables. The modelling carried out in this study detected two dynamic systems, which matched the distribution of the molecular clans. One system was centralised in the Bay of Plenty matching the New Zealand endemic clan. The other involved a dynamic system that encompassed four other regions on both coasts of the country that matched the distribution of the other clans. By combining the results it was possible to propose a framework for Physalia distribution including a mechanism that has driven clan divergence. Moreover, potential blooming areas that are notoriously hard to establish for jellyfish were hypothesised for further study and/or validation.

Many members of the Phylum Cnidaria are mutualistic with unicellular dinoflagellates belonging to the genus Symbiodinium. Corals are the most widely recognized example of these associations due to their key ecological importance in coral reef ecosystems where they serve as the structural and trophic foundation of these rich ecosystems. Coral reefs are severely threatened by human activities worldwide and are at great risk from global climate change, in particular the increase in seasurface temperatures. Detailed knowledge of how corals respond to stress is scarce. The most serious and immediate response of corals to environmental stress is a process referred to as coral bleaching (a.k.a. cnidarian bleaching). Nevertheless, the cellular and molecular processes by which elevated temperatures elicit the bleaching response are poorly understood. This dissertation deals with this important question by describing two mediators of cnidarian bleaching in the model symbiotic tropical sea anemone Aiptasia pallida (Verril), namely nitric oxide and cyclophilin. After an introduction to the topic of cnidarian-algal symbioses and cnidarian bleaching (Chapter 1), I present results from a study describing the involvement of nitric oxide (NO) in the anemone A. pallida (Chapter 2). Elevated temperature as well as oxidative stress induces production of NO and exposure of A. pallida to NO induces bleaching at non-stressful temperatures. Co-incubation with an NO scavenger suppresses bleaching. I propose that the host up-regulates NO production in response to elevated oxidative stress and that this situation leads to cytotoxicity and bleaching. Chapter 3 examines the role of cyclophilin from A. pallida in the regulation of the symbiosis. Cyclophilins belong to a highly conserved family peptydyl-prolyl cistrans isomerases (PPIases). Incubation of A. pallida with cyclosporin A (CsA), a potent inhibitor of cyclophilin resulted in bleaching and a decrease in tolerance to elevated temperatures. Protein extracts from A. pallida exhibited CsA-sensitive PPIase activity. Laser scanning confocal microscopy using superoxide and nitric oxide-sensitive fluorescent dyes on live A. pallida revealed that CsA strongly induced the production reactive oxygen species as well as NO. We tested weather the CsAsensitive isomerase activity is important for maintaining the activity of the antioxidant enzyme superoxide dismutase (SOD). SOD activity of protein extracts was not affected by pre-incubation with CsA in vitro. In Chapter 4 I review what is known about the molecular and cellular mechanisms of bleaching and describe a model of bleaching based on the results presented herein as well as studies of non-cnidarian models. / Graduation date: 2007

La présence d’un récepteur de type RXR a récemment été rapporté chez la pensée de mer, Renilla koellikeri, de même que chez d’autres anthozoaires, et le NO semble jouer des différents rôles physiologiques, chez plusieurs cnidaires. L’acide rétinoïque (AR) et le monoxyde d’azote (NO) sont connus pour leur implication dans l’induction de la croissance des neurites chez les vertébrés ainsi que chez les invertébrés. Mais jusqu’à présent, aucun rôle de ces agents n’a encore été identifié chez ce phylum ancien des invertébrés. Dans le but de montrer que ces agents morphogénétiques ont un rôle dans le développement neuronal chez ces ancêtres des métazoaires bilatéraux, nous avons utilisé des cultures primaires de cellules du cnidaire anthozoaire Renilla koellikeri (pensée de mer), doté d’un système nerveux des plus primitif. Nous avons trouvé que les deux types d’acide rétinoïque, 9-cis et 11-trans, induisent une prolifération cellulaire dose-dépendante en fonction du temps dans les boîtes de pétri enduites de polylysine. Les cultures cellulaires exposées à l’acide rétinoïque dans les boîtes sans polylysine montrent une différenciation en des cellules épithéliales. D’autre part, le NO induit exclusivement une différenciation neuronale dans les boîtes enduites de polylysine. Aucun autre type de cellules subit un différenciation en présence de NO et la densité des cellules dédifférenciées a diminué. Les prolongements des neurones différenciés semblent s’enchevêtrer et former un réseau neuronal assez dense. L’ensemble de ces observations suggère que l’acide rétinoïque, contrairement à NO, est associé à l’activité mitotique, et que l’acide rétinoïque et le NO sont impliqués différemment dans la spécification cellulaire, respectivement épithéliale et neuronale, chez la pensée de mer. Le type d’action déclenchée, qu’il soit la mitogénèse ou la différenciation (épithéliale ou neuronale), varie alors selon l’état d’adhésion des cellules au substrat. Comme les données moléculaires et paléontologiques rapprochent les cnidaires, telle la pensée de mer, des ancêtres des eumétazoaires, nos résultats suggèrent que le rôle morphogénétique de l’acide rétinoïque et du NO est enraciné dans l’ancêtre commun de tous les métazoaires. / Retinoic acid receptors were recently reported in the sea pansy, Renilla koellikeri, and in other anthozoans, and NO seems to play various roles in several cnidarians. Retinoic acid (RA) and nitric oxide (NO) are known for their implication in inducing neurite outgrowth in both vertebrates and invertebrates. But so far, no role of these agents has been identified in this basal metazoan phylum. In order to show that these agents have a morphogenetic role in neuronal development in the ancestors of bilateral metazoan. We used primary cultures of cells from the cnidarian anthozoan Renilla koellikeri (sea pansy), with the most primary nervous system. We found that both 9-cis and 11-trans retinoic acid induced cell proliferation in dose- and time-dependant manners in petri dishes coated with polylysine. Cell cultures exposed to retinoic acid in dishes devoid of polylysine were observed to differentiate into epithelial cells. On the other hand, NO induced extensive neurite outgrowth in polylysine-coated culture dishes. No other celle type underwent differentiation in the presence of NO, and the density of dedifferentiated cells was reduced. The neurites of the differentiating neurons appeared to intertwine and form a loose nerve net. These observations suggest that retinoic acid, but not NO, has mitogenic activity, and that retinoic acid and NO are differentially involved in nerve cell specification in the sea pansy. The type of action, mitogenesis or cell differenciation (epithelial or neural), depends on the degree of cell adhesion to substrate. As both molecular and paleontological evidence place cnidarians such as the sea pansy closest to the eumetazoan ancestor, our results suggest that the morphogenetic role of retinoic acid and NO was rooted in the commun ancestor of all metazoans.

Nausithoe aurea Silveira & Morandini, 1997 é uma espécie metagenética e dióica com fecundação externa. Os oócitos são liberados continuamente (55 dias em laboratório), porém com grandes variações no número a cada dia. No desenvolvimento embrionário a clivagem, após o estágio de 8 células, passa de holoblástica e igual para pseudoespiral. A gastrulação ocorre por ingressão multipolar e inicia-se aproximadamente 24 horas após a fecundação. A estrutura histológica geral das gônadas assemelha-se a outros Scyphozoa, onde os gonócitos proliferam a partir da gastroderme, migram e diferenciam-se na mesogléia. Na gônada masculina as células germinativas formam camadas razoavelmente distintas e constituem folículos testiculares. Na gônada feminina os oócitos surgem da zona germinativa na gastroderme e apresentam um gradiente de maturação a partir deste ponto (cortes no sentido oral-aboral). Os oócitos encontram-se livres na mesogléia da gônada, sem associação com outras células. A relação espacial entre a musculatura circular, as gônadas e o sulco coronal, é uma característica a ser usada na sistemática do gênero Nausithoe Kölliker, 1853. / Nausithoe aurea Silveira & Morandini, 1997 is a metagenetic and dioecious species with external fertilization. The oocytes are released continuously (55 days in laboratory), but with great variations in the daily number. In the embryonic development the cleavage, after the 8 cells stage, changes from holoblastic and adequal to pseudospiral. The gastrulation occurs through multipolar ingression and begin 24 hours after fertilization. The general histological structure of the gonads resembles other Scyphozoa, in which the gonocytes proliferate from the gastrodermis, migrate and differentiate in the mesoglea. In the male gonad the germ cells are arranged in distinctive layers and form follicles (cysts). In the female gonad the oocytes develop from the germinative zone in the gastrodermis and present a maturing gradient from this point on (oral-aboral sections). The oocytes are free in the gonad mesoglea, without association to any cell. The spatial relation of the coronal musculature, gonads and coronal groove, is a character to be used in the systematics of the genus Nausithoe Kölliker, 1853.

Os ciclos de vida de Clytia linearis (Thornely, 1899) e de duas espécies apresentando caracteres considerados diagnósticos de Clytia gracilis (M. Sars, 1850) – aqui denominadas Clytia cf. gracilis sp. 1 e Clytia cf. gracilis sp. 2 – foram estudados com base em espécimes coletados no infralitoral raso da costa de São Sebastião e Ilhabela, sudeste do Brasil, entre fevereiro de 1999 e abril de 2000. Medusas foram cultivadas em laboratório, a temperatura de 22-24oC. Colônias de C. linearis são monossifônicas, simpodiais, com até 21,5mm de altura e portando até 26 hidrantes e 10 gonângios. Medusas adultas, alcançando 2,5-3,6mm de diâmetro e até 29 tentáculos e 28 estatocistos, podem ser distinguidas de outras espécies de Clytia pela presença de nematocistos microbásicos mastigóforos do tipo C. Medusas adultas de Clytia cf. gracilis spp. 1 e 2 podem ser distinguidas das demais espécies do gênero estudadas até o momento pela presença de uma fileira de nematocistos microbásicos mastigóforos do tipo A na umbrela, no nível do canal circular. Medusas adultas de C. cf. gracilis sp. 1 e C. cf. gracilis sp. 2 apresentam até 16 tentáculos e podem ser distinguidas entre si pelo diâmetro da umbrela: 6,6-10,1mm e 3,6-5,5mm, respectivamente. Quanto ao estágio de pólipo, C. cf. gracilis sp. 1 apresenta usualmente colônias dicotômicas eretas, hidrotecas alongadas, e gonotecas na hidrorriza e pedículos. Estes caracteres concordam com a descrição de C. gracilis, mas as espécies diferem entre si pela morfometria das gonotecas e dos nematocistos microbásicos mastigóforos do tipo B: aproximadamente 15mm de comprimento para C. gracilis e 9-10mm para C. cf. gracilis sp. 1. Por outro lado, nematocistos do tipo B de C. cf. gracilis sp. 2, com aproximadamente 14,5mm de comprimento, em média, são morfometricamente semelhantes aos de C. gracilis. No entanto, C. cf. gracilis sp. 2 difere de C. gracilis pela forma da hidroteca, por apresentar gonotecas apenas na hidrorriza, e pelo hábito polissifônico do colônias bem desenvolvidas. Uma terceira espécie, C. cf. gracilis sp. 3, é descrita com base em uma colônia sem gonângios. Aspectos da sistemática de Clytia são discutidos. / he life-cycles of Clytia linearis (Thornely, 1899) and two species with characters considered diagnostic of Clytia gracilis (M. Sars, 1850) – Clytia cf. gracilis sp. 1 and Clytia cf. gracilis sp. 2 – have been studied based on specimens collected in the shallow subtidal coast of São Sebastião and Ilhabela, southeast Brazil, between February 1999 and April 2000. Medusae were cultured in the laboratory (22-24oC). Colonies of C. linearis are monosiphonic, sympodial, up to 21.5mm high and bearing up to 26 hydranths and 10 gonangia. Adult medusae reached 2.5-3.6mm in diameter, and up to 29 tentacles and 28 statocysts. The presence of microbasic mastigophore type C nematocysts distinguishes adult medusae of C. linearis from other species of Clytia. A band of microbasic mastigophore type A nematocysts in the umbrella, at the level of the circular canal, distinguishes adult medusae of Clytia cf. gracilis spp. 1 and 2 from other species of the genus. Adult medusae of C. cf. gracilis sp. 1 and C. cf. gracilis sp. 2 have up to 16 tentacles, and can be distinguished by the diameter of the umbrella: 6.6-10.1mm and 3.6-5.5mm, respectively. Colonies of C. cf. gracilis sp. 1 are usually erect and dichotomous, the hydrothecae are elongated and the gonothecae present in the hydrorhiza and pedicels. These features closely match with the description of C. gracilis, but both species differ in the morphometry of the gonothecae and microbasic mastigophore type B nematocysts: about 15mm (length) for C. gracilis and 9-10mm for C. cf. gracilis sp. 1. Type B nematocysts of C. cf. gracilis sp. 2 (about 14.5mm in length) are more similar in size to those of C. gracilis. However, the former species differs from the latter in the shape of the hydrothecae, by having gonothecae only at the hydrorhiza and polysiphonic well-developed colonies. A third species, C. cf. gracilis sp. 3, is described based on an unfertile colony. Aspects of the systematics of Clytia are discussed.