Les Porpitidae forment une famille de cnidaires hydrozoaires pélagiques, aussi appelés chondrophores. Sommaire. 1 Description et caractéristiques; 2 Liste. La famille des Hydridae est une famille d’animaux de l’embranchement des cnidaires (les cnidaires sont des animaux relativement simples, spécifiques du. L’endosymbiose trophique établie entre un hôte animal du groupe des Cnidaires et ses symbiotes Dinoflagellés photosynthétiques du genre.
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Conceived and designed the experiments: Life cycles cmidaires medusozoan cnidarians vary widely, and have been difficult to document, especially in the most recently proposed class Staurozoa. However, molecular kes can be a useful tool to cnidairres medusozoan life cycles by tying together different life history stages.
Genetic data from fast-evolving molecular markers mitochondrial 16S, nuclear ITS1, and nuclear ITS2 show that cnidaites that were presumed to be a hydrozoan, Microhydrula limopsicola Limnomedusae, Microhydrulidaeare actually an early stage of the life cycle of the staurozoan Haliclystus antarcticus Cnidqires, Lucernariidae.
Similarity between the haplotypes of three markers of Microhydrula limopsicola and Haliclystus antarcticus settles the identity of these taxa, expanding our understanding of the staurozoan life cycle, which was thought to cnidaaires more straightforward and simple. The consequences are likely to be replicated in other medusozoan groups.
For instance we hypothesize that other species of Microhydrulidae are likely to represent life stages of other species of Staurozoa. As with other organisms displaying complex life cycles, documenting all the life history stages in medusozoan species is an enormous challenge. The usual approach has been to attempt to rear species through their various life stages in the laboratory.
However, each life stage is adapted for different and often unknown conditions, making the task difficult, time consuming, and in many cases so far, impossible. Because the genome is the same in different life history stages of any given species, molecular data provide another tool that can help elucidate medusozoan life cycles by tying together different life stages.
While there is great variation in medusozoan life cycles, there exist some broad-scale patterns of congruence between life cycle differences and the origins of major medusozoan taxa suggesting that evolutionary changes in life cycle have sometimes corresponded to the establishment of distinct lineages.
One of the most intriguing findings from these phylogenetic studies has been the hypothesis that the Stauromedusae so-called stalked jellyfishes form an cniidaires medusozoan clade that is separate from Scyphozoa Coronatae and Discomedusaewithin which Stauromedusae was traditionally classified . Because of its distinct origin and some putatively unique life history characteristics, Marques and Collins  established the class Staurozoa and noted that the finding raises important issues about the evolution of cnidarian development and life cycles.
The present view holds that the life cycle of staurozoans is relatively simple, consisting of a planula larva that attaches to the substrate and grows into a primary polyp, which subsequently undergoes an apical transformation into the adult form. Because the transformation to adult takes cnidaiees without fission or budding, this development results in a mosaic individual, in which the structures of xnidaires oral part are similar to those of an adult medusa particularly scyphozoans and cubozoanswhereas the basal part retains characteristics of the sessile polyp .
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However, knowledge of staurozoan development is based on a handful of observations on a small cnisaires of species. Studies about juvenile stauropolyp development include only Haliclystus octoradiatus Lamarck,  and two species of StylocoronellaS. Polyps of cnidaaires latter species are interstitial and it is unknown whether or not this cnidalres condition is common in the group.
Based on analyses of nuclear genes coding for the small and large subunits of the ribosome SSU or 18S and LSU or 28S, respectivelyCollins and co-workers  suggested that the diminutive polyp form of the Antarctic species Microhydrula limopsicolaoriginally described by Jarms and Tiemann  in the class Hydrozoa Trachylina, Limnomedusaecould be an unknown life stage of a species of Stauromedusae.
The hypothesis was immersed in a broader analysis of the phylogeny and evolution of Trachylina, and many issues remain unattended: The goal of this study is to address these questions, cnidaifes new molecular and morphological evidence to this conundrum.
Specimens of Haliclystus antarcticus Pfeffer, from Antarctica Figure 2 were collected manually during low tide tide prediction between 0.
Specimens of the Chilean Haliclystus antarcticusoriginally mis identified as H. Zagal  and J.
Classification des Cnidaires de l’Europe de l’Ouest
Stars are records of Haliclystus antarcticus: Pictures from Morandini, AC. Sequences included in our analysis were derived for this study or have come from GenBank Table 1. The markers were already adopted and proved to be efficient for the species level identification in Medusozoans 16S-  ; ITS- . To confirm molecular data, the sequences of M. Uncorrected pairwaise distances were calculated in Bioedit.
Gaps were treated as missing data. The most appropriate model for each of the datasets was chosen by employing the Akaike information criterion AIC. The cladograms show that M. Haliclystus antarcticus from Chile forms a clade with these specimens and is only slightly diverged from them.
Bootstrap indices under both MP and ML respectively at each node. Topologies are congruent under MP and ML analysis. All ten sequenced specimens of Cnidaiers. Species of stauromedusae, for which we led more than one haplotype H.
Collins and co-workers  did not formally establish a synonym for Lew limopsicola.
However, a very close relationship of M. Our analyses are obviously constrained by the non-availability of other cultures or samples of M. With increased taxon sampling and data from fast-evolving markers, we conclude that M. Several points support this conclusion. While intraspecific variation of these genetic markers is not very well known for species of stauromedusae, available data indicate that some intraspecific genetic variation exists, and that it is smaller than observed interspecific variation compare Table 3 with Table 2.
This would suggest that identity in these genetic markers can only happen if the samples are taken from the same species. Finally, one might question whether there are other Antarctic species of Haliclystus that could confound our identification of Microhydrula limopsicola as H.
With the remainder of the discussion, we synthesize the relevant historical literature to address the implications of our identification of M. The implications of this synonymy for the family Microhydrulidae were only briefly touched upon by Collins and co-workers . The family Microhydrulidae Hydrozoa, Limnomedusae encompassed three species in two genera: Microhydrula pontica Valkanov,M. One is now clearly established as a stauromedusa.
It remains to be explicitly tested whether M. We note that M. Sars,Lucernariopsis campanulata Lamouroux, and Craterolophus convolvulus Johnston,  have also been found. Of course, additional data, particularly genetic data, from other species of Microhydrulidae are necessary to test our hypothesis that these species represent stages in the development of species of Stauromedusae. As a result, M. No doubt the scarce literature on early stages of staurozoans made it difficult to establish reliable comparisons among taxa.
Even though dissimilarities are evident there are several morphological similarities between M. Moreover, both lack mouth and a permanent gastrovascular cavity necessitating intracellular digestion .
A further similarity is the production of frustules . More specifically, the settled, rounded up planula of H. Likewise, the frustules of Microhydrulidae are formed from a lateral budding of the body . The planulae of H. These protuberances, which are provided with numerous nematocysts, result from a local thickening of the ectoderm and seem to play an important role in prey capture prior to the development of tentacles . Homology between the protuberances, found in H.
However, the cauliflower structure can also be a simple result of a strong aggregation of larvae see below  since at a more advanced stage, the larva of H. Another interpretation is that the development of H. Recently metamorphosed individuals of Haliclystus borealis Uchida,H. A—C different stages of M. D—E process of frustulation observed in both species: D planula of H.
F—G possible correspondences of stages of both species: F a group of H. The hemispherical shape and the production of frustules A, D, E are similar in settled planulae of H.
The same gregarious behavior to feeding was observed in both species B, F. At a more advanced stage, the larva of H. Figures modified from . Histological similarities between M. Stalks of adult individuals of the genus Haliclystus also present fibrillar components at the attachment sites .
In addition, the endoderm of M. One feature remarked by Jarms and Tiemann  and Collins and co-workers  is the cnidome, with microbasic euryteles being present in M. This nematocyst type is a common feature of H. Accepting the identity of M. Indeed, nematocysts of the creeping planula larvae of Haliclystus salpinx Clark, are different from the adults of the same species . The planula larval stage of H. Based on our finding that M.
Thus far, early stages of the cnnidaires cycle of H. In fact, few staurozoan pre-adult stages are known. Only the creeping benthic planula cnidaiers of H. Therefore, it is presently impossible to assert that the Microhydrula stage is present in all species of Staurozoa. Similarly, it is unclear how widespread the presence of frustule stages is in other stauromedusae.
Nevertheless, we suggest that the study of sediments and potential associations with overlooked substrata e. The main life cycle was based on for H. Stauropolyp stage and its ability to create frustules white arrows are hypothesized based on observations of Stylocoronella .
Figures modified from . We hypothesize that this stage occurs right after the settlement of the planula cnidalres or sometime after the settlement of the frustuleadding a stage Figure 5 to the hypothetical cniddaires cycle proposed for staurozoans, since the best known life cycle of a staurozoan, the odd psammic Stylocoronella lea.
Settlement of planulae occurs in groups of 3—20 individuals in H. Experimental procedures restricting larval aggregation of H.