The life cycle of Chrysaora lactea Eschscholtz, 1829 (Cnidaria,Scyphozoa) with notes on the scyphistoma stage of three other species

The life cycle of Chrysaora lactea Eschscholtz, 1829, a common species on the Brazilian coast, is described. Mature medusae were collected and isolated in a planktonkreisel, whereupon planulae appeared after 1–2 days. These planulae settled and metamorphosed into polyps. Fully developed scyphistomae typically possessed 16 tentacles, and on strobilation produced from 2 to 10 ephyrae. The ephyrae were transparent and had characteristic nematocyst warts on the exumbrella. Tentacles first appeared near the margin on the subumbrella. Ephyrae and young medusae were maintained in laboratory conditions up to 7 months.     

Stephanoscyphus eumedusoides n. spec. (Scyphozoa,Coronatae), ein Höhlenpolyp mit einem neuen Entwicklungsmodus

The new solitary scyphopolypStephanoscyphus eumedusoides was detected in submarine caves of the rocky shore near Marseille (Mediterranean Sea), where it lives attached to colonies of corals at a depth of 2–3 m to 40–50 m. The new mode of development has been described briefly in an earlier paper in which the polyp was given the preliminary nameTesseroscyphus eumedusoides (Werner 1971a) but by a more detailed investigation it proved to belong to the genusStephanoscyphus. The essential characteristics of the peridermal tube and the soft body are outlined. Most of them are not sufficient to identify significantly the new species. Identification was possible by the observations on the new mode of development by sessile medusoids which is unique in the order Coronatae and the class Scyphozoa. The medusoids originate in the normal way by the process of strobilation. But other than in the known scyphozoan development by which free-swimming young medusae are produced, the medusoids remain connected with each other and the basal residue of the polyp's body within the peridermal tube. Development, morphology and anatomy of the medusoids are described. As they exhibit essential medusan characteristics they belong to the type of eumedusoid. On the other hand, there are remarkable signs of reduction due to progressive steps of evolution. The hermaphroditic medusoids become mature and reproduce within the polyp's tube. The fertilized eggs develop within the gastric cavity of the medusoids into free-swimming planulae which are released by the chain of degenerating and dying medusoids being pushed out of the tube by the regenerating polyp. After a planktonic period of several weeks, the planula attaches to a substratum in the normal way and undergoes development into the young polyp. This is described briefly. The cnidom of the polyp, the medusoid, and the planula consists of holotrichous haplonemes and heterotrichous microbasic euryteles. The vertical and horizontal distribution, and some details of the ecology are outlined according to the present state of knowledge. Because the new species has been collected and found only in submarine caves it is considered to be a true cave-living animal. Its diagnosis is given.     

Evolution and development of scyphozoan jellyfish

Scyphozoan jellyfish, or scyphomedusae, are conspicuous members of many ocean ecosystems, and have large impacts on human health and industry. Most scyphomedusae are the final stage in a complex life cycle that also includes two intermediate stages: the larval planula and benthic polyp. In species with all three life‐cycle stages, the metamorphosis of a polyp into a juvenile scyphomedusa (ephyra) is termed strobilation, and polyps can produce one ephyra (termed monodisc strobilation) or many ephyrae (termed polydisc strobilation). In contrast to species with planula, polyp and medusa stages, a handful of scyphozoan species possess modified life cycles with reduced or absent stages. The evolutionary patterns associated with strobilation and life‐cycle type have not been thoroughly investigated, and many studies of ephyra development and strobilation induction are not yet synthesized. Herein, I place the development of scyphomedusae in an evolutionary context. I first review the current evolutionary hypotheses for Scyphozoa. Next, I review what is known about scyphomedusa development across a broad diversity of species, including the first signs of strobilation, the formation of strobila segments, and the morphogenesis of ephyrae. I then review cases where the canonical scyphozoan life cycle has been modified, and take advantage of phylogenetic hypotheses to place these observations in an evolutionary context. I show that the evolution of monodisc strobilation occurred at least twice, and that the loss of intermediate life‐cycle stages occurred several times independently; by contrast, the reduction of the medusa stage appears to have occurred within a single clade. I then briefly review the major natural cues of strobilation induction. Finally, I summarize what is currently known about the molecular mechanisms of strobilation induction and ephyra development. I conclude with suggestions for future directions in the field.     

Effect of variable phases of tide cycle on reproduction of Laomedea flexuosa (Hydroidea, Thecaphora

Colonial hydroid Laomedea flexuosa inhabits the narrow belt of low littoral zone in the White Sea. What is a reason of so limited habitat? The authors studied the time of planulae release and its behavior during free swimming stages and settlement of larvae in nature and under laboratory conditions. Three methods were used to registrate the tidal dependent dynamic of planulae release: 1) plankton collecting bags around Fucus inflatus kelp with mature hydroids colonies; 2) active stirring kelps with hydroids in container with water, which is an old way to stimulate planulae release; 3) direct account of the mature planulae into gonangia. The dynamic of intensity of L. flexuosa planulae release was investigated according 3-4 phases of tidal cycle. All data were statistically tested. For L. flexuosa a moment of general larvae release was found in phase with the period of low water. This correlation could explain strict limitation in occurrence of L. flexuosa only in the lower part of intertidal zone. Laboratory experiments show that planulae release is stimulated by littoral drainage, and renewal of water movement during the beginning of tide. The decrease in time of planulae settlement is an affective way for marine sedentary species to stay in a narrow zone of optimal habitat.     

Effects of temperature and light intensity on asexual reproduction of the scyphozoan, <Emphasis Type="Italic">Aurelia aurita</Emphasis> (L.) in Taiwan

Jellyfish blooms cause problems worldwide, and they may increase with global warming, water pollution, and over fishing. Benthic polyps (scyphistomae) asexually produce buds and small jellyfish (ephyrae), and this process may determine the population size of the large, swimming scyphomedusae. Environmental factors that affect the asexual reproduction rates include food, temperature, salinity, and light. In this study, polyps of Aurelia aurita (L.), which inhabit Tapong Bay, southwest Taiwan, were tested in nine combinations of temperature (20, 25, 30°C) and light intensity (372, 56, and 0 lux) in a 12 h light–12 h dark photoperiod. Production of new buds decreased with warmer temperature and stronger light intensity. Warm temperature accelerated strobilation and increased the daily production of ephyrae. The proportion of ephyrae of total asexual reproduction (new buds + ephyrae) increased dramatically in warmer temperature and more light. Survival was reduced in the highest temperature. Strobilation did not occur in the lowest temperature in darkness. All measures of total asexual reproduction indicated that mid- to high temperatures would lead to faster production of more jellyfish. Continuous high temperatures might result in high polyp mortality. Light affected asexual reproduction less than did temperature, only significantly accelerating the strobilation rate. Because the interactive effects of light and temperature were significant for the time period polyps survived and the potential production of jellyfish polyp⁻¹, combined light and temperature effects probably are important for strobilation in situ. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Early Life History of the ‘Irukandji’ Jellyfish Carukia barnesi

Adult medusae of Carukia barnesi were collected near Double Island, North Queensland Australia. From 73 specimens, 8 males and 15 females spawned under laboratory conditions. These gametes were artificially mixed which resulted in fertilized eggs. Post fertilization, most eggs developed to an encapsulated planula stage and then paused for between six days and six months prior to hatching as ciliated planulae. The paused stage planulae were negatively buoyant and adhered to substrate. The first planula was produced six days post fertilization, lacked larval ocelli, remained stationary, or moved very slowly for two days prior to metamorphosis into primary polyps. Mature polyps reproduced through asexual reproduction via lateral budding producing ciliated swimming polyps, which in turn settled and developed into secondary polyps. Medusae production for this species was in the form of monodisc strobilation, which left behind polyps able to continue asexual reproduction.     

Effects of low salinity on settlement and strobilation of scyphozoa (Cnidaria): Is the lion’s mane <Emphasis Type="Italic">Cyanea capillata</Emphasis> (L.) able to reproduce in the brackish Baltic Sea?

Several species of scyphozoan medusae occur in river estuaries and other brackish waters but it is often unknown if the planulae settle and the scyphopolyps reproduce in those low-salinity waters. In the present study, scyphozoan species from the German Bight (North Sea) were tested in laboratory experiments to investigate their tolerance of low salinity. Planula larvae released from medusae in salinity 32 were still active after the salinity was reduced to 10 (Cyanea capillata, Cyanea lamarckii) and to 7 (Chrysaora hysoscella) in laboratory treatments. Planulae did not settle on the undersides of floating substrates when salinity was reduced to <20. By contrast, planulae released from C. capillata medusae in Kiel Bight (western Baltic Sea) in salinity 15 developed into polyps in laboratory cultures. Polyps reared from planulae in salinity 36 survived a reduction to 12 (C. capillata, C. lamarckii) and to 8 (Aurelia aurita). Polyps of all tested species strobilated and released young medusae (ephyrae) in salinity 12. These results show a high tolerance of planulae and polyps to low salinity, indicating their possible occurrence in estuaries and brackish waters. In addition to laboratory observations, young C. capillata ephyrae were collected in the western Baltic Sea (Kiel Bight) in salinity 15, which indicates that they were probably released by a local polyp population. We suggest that the polyps of the painfully stinging lion’s mane, C. capillata, may be more widespread in the Baltic Sea than previously assumed and that the occurrence of the medusae may not only depend on inflow of water masses from the North Sea.     

Release and growth of Cyanea capillata (L.) ephyrae in the Gullmar Fjord,western Sweden

In an investigation carried out in the Gullmar Fjord, western Sweden, the autecology of the scyphozoans Aurelia aurita (L.) and Cyanea capillata (L.), has been studied. This paper focuses on results concerning C. capillata, but comparisons with Aurelia aurita are made and discussed. The main period of strobilation was in winter and early spring. The extent of ephyrae release was only one tenth of that of A. aurita. The period of rapid growth of ephyrae and medusae during the spring was delayed one month compared to the pattern for Aurelia. The Cyanea scyphistomae are exposed to predation by the nudibranch Coryphella verrucosa and only very limited settling of Cyanea planulae occurred in the area. Immigration from the North Sea is probably a major factor regulating the appearance of Cyanea capillata along the western coast of Sweden.     

D-Methionine and gold chloride alleviate adverse effects of glutamate on motility of ephyrae of Aurelia aurita (Linnaeus, 1758) (Scyphozoa: Semaeostomeae)

Glutamate (MSG) causes low pulse numbers and swimming cessation in Aurelia jellyfish ephyrae. Ephyrae given MSG for 1h and subsequently maintained in artificial sea water (ASW) were observed at 1, 3, 24, and 48 h intervals. Abnormality of motility was found at all post-treatment periods but some ephyrae resumed swimming and normal pulsing within 48 h. Swimming and pulsing were impaired in a significant number of ephyrae within 15 min of MSG treatment. The mechanism of MSG action on ephyrae motility is unknown, but glutamate damage to neurons and hair cells of higher animals is partly attributed to the formation of reactive oxygen species (ROS). Laser confocal fluorescent microscopy of ephyrae following MSG treatment indicated an increase of calcium and free radicals in the ephyrae as early as 5 min following MSG exposure. To determine whether antioxidants could alleviate MSG effects, we exposed ephyrae to gold chloride before, during, and after treatment with MSG. Ephyrae given gold chloride pre-treatment for 1h and then transferred into gold chloride plus MSG for 1h showed statistically significant recovery from MSG impairment of pulsing at the 3, 24, and 48 h post-glutamate time periods and higher numbers of swimmers at 3 h and 24 h. Ephyrae groups given gold plus MSG but without gold pretreatment showed recovery of swimming at 24 h and pulsing at 48 h. d-methionine given simultaneously with MSG significantly improved the pulse numbers and swimming of ephyrae at the 3, 24, and 48h post-glutamate time periods compared to those receiving MSG alone. Both d-methionine and gold chloride accelerated the time of recovery from glutamate-induced motility impairment, possibly through their antioxidant activities.     

Fish assemblage structure in urban streams of Puerto Rico: the importance of reach- and catchment-scale abiotic factors

Cotylorhiza tuberculata is a common symbiotic scyphozoan in the Mediterranean Sea. The medusae occur in extremely high abundances in enclosed coastal areas in the Mediterranean Sea. Previous laboratory experiments identified thermal control on its early life stages as the driver of medusa blooms. In the present study, new ecological aspects were tested in laboratory experiments that support the pelagic population success of this zooxanthellate jellyfish. We hypothesized that planulae larvae would have no settlement preference among substrates and that temperature would affect ephyra development, ingestion rates and daily ration. The polyp budding rate and the onset of symbiosis with zooxanthellae also were investigated. Transmission electron microscopy revealed that zooxanthella infection occurred by the polyp stage. Our results showing no substrate selectivity by planulae and high polyp budding rates in high temperatures suggest increased benthic polyp populations, which would lead to higher medusa abundances. Rates of transition from ephyrae to medusae and the feeding of early medusa stages also increased with temperature. Continuing changes in coastal ecosystems such as future climate warming and marine construction may lead to increased populations of jellyfish to the detriment of fish globally.     

Groups travel further: pelagic metamorphosis and polyp clustering allow higher dispersal potential in sun coral propagules

We report that planulae produced by Tubastraea coccinea can metamorphose and aggregate in groups of up to eight polyps in the water column, without previous settlement on benthic substrate. We also evaluated the survival of propagules to test whether different levels of aggregation allowed for longer planktonic life and, therefore, higher dispersal potential. Our results show that pelagic polyps live longer than planulae, probably because they can feed and meet the presumably high-energy demands of swimming. Clusters of two or more individuals lived longer than solitary polyps. However, mortality did not differ between small (2–3 polyps) and large (4–8 polyps) clusters, suggesting the existence of an upper limit to cluster size. Most swimming clusters (80 %) remained alive after 6 months, suggesting that pelagic metamorphosis and cluster formation can be a key life-history feature increasing dispersal potential, population connectivity, and the colonization of new habitats in this invasive species.     

Rhopalium development in Aurelia aurita ephyrae

Rhopalia of developing ephyrae were examined using the SEM and TEM at 24 h intervals following strobilation induction. Kinocilia are shorter in the ephyra stage than in polyps. A few ephyra-type kinocilia are found in rhopalia as early as 24 h after induction, before a distinct rhopalium is seen. By 72 h, the shorter kinocilia predominate and are almost as numerous as in ephyrae (120 h). Many of the kinocilia are associated with mechanoreceptor cells (MR) found in the rhopalia. These MR cells are compared to those reported for medusae. Although newly released ephyrae lack a touch plate, the MR cells in their rhopalia along with the statocyst and neuromuscular system apparently enable these organisms to detect and respond to gravity.     

Environmental factors inducing the transformation of polyp into medusae in <Emphasis Type="Italic">Aurelia aurita</Emphasis> (Scyphozoa)

The transformation of polyp into medusa is one of the most interesting processes in the life cycle of cnidarians. In the polyps of the class Scyphozoa this transformation occurs in the form of strobilation, which is the transverse fission of polyps with the formation of discoidal ephyrae. At present, the endogenous regulation of strobilation in one of scyphozoans, Aurelia aurita, is being investigated by the methods of molecular biology (Fuchs et al., 2014). However, it is still unclear which key environmental factors induce this process. The main purposes of this review are to summarize the literature data on the conditions in which strobilation in A. aurita occurs in nature and in the laboratory and to try to identify the environmental factors that are most likely to play a signaling role in strobilation.     

Weitere Untersuchungen zur Morphologie,Verbreitung und Ökologie vonStephanoscyphus planulophorus (Scyphozoa,Coronata)

The solitary scyphopolypStephanoscyphus planulophorus Werner, 1971 was detected in the submarine caves of the French Mediterranean coast near Marseille, and on the Sorrent Peninsula as well as near the Isle of Ischia (Italy). It was rare at the French sites studied but in the Italian caves of the upper sublittoral it proved fairly abundant. Its life history is unique because (a) the medusa generation is reduced to a transitional embryonic stage, and (b) no germ cells could be traced in any phase. The polyps reared in the laboratory gave rise to several continuous generations. Thus, previous observations on their morphology, distribution and ecology could be completed. Growth and size (defined as length of the peridermal tube) are analyzed, and calculations of the form quotient D/L (D = upper diameter, L = length of tube) are given. Observations on the structure of peridermal teeth which mark the inner wall of the tube in its basal parts indicate that (a) shape is a characteristic of diagnostic value and (b) number and symmetrical arrangement can be described by the formula 4 P + 4 I + 8 A (B; 5–7). A discontinuous circle of whitish pigment spots restricted to the endodermal cells of tentacle bases is another mark of diagnostic value confined to the soft body.S. planulophorus has a bicnidom of holotriches isorhizas and heterotrich microbasic euryteles. Size and distribution of nematocysts are listed for the life-cycle phases. The difference in distribution and population density between the sites near Marseille and Naples can be explained by local differences of water temperature and the thermal requirements of the polyp, the strobilation phase of which is temperature-sensitive. According to the present state of knowledge,S. planulophorus is one of the few true cave-living scyphopolyps. Considering the evolutionary consequences, the particulars of its life cycle can be interpreted as an adaptation to the special habitat conditions. The evolutionary progress of medusa reduction as well as the disadvantage of apogamous propagation are discussed briefly. A diagnosis is given based on the new morphological observations.     

白色霞水母生活史的实验室观察

本文首次描述了白色霞水母从受精卵至碟状体的生活史。(1)包括受精卵、卵裂、囊胚以及浮浪幼虫等在内的胚胎发育各期均在开放的水体中,在20·8 -21·4℃浮浪幼虫于受精后14 h出现; (2)浮浪幼虫在定置前形成一种凸面的圆形浮浪幼体囊,除了浮浪体囊外,螅状体还可产生足囊和通过产生匍匐茎形成囊胞进而发育成新的螅状体; (3)尽管偶而产生2个碟状体但仍为典型的单碟型横裂; (4)新释放的碟状幼体绝大多数为8个缘叶, 8个感觉棍和8对钝圆的缘瓣,但畸形个体最多12个,最少6个缘叶; (5)雌雄个体间的交互作用对产卵和受精是非常重要的因子[动物学报52 (2) : 389 -395 , 2006]。     

Cytologische Veränderungen während der Metamorphose des CubopolypenTripedalia cystophora (Cubozoa,Carybdeidae) in die Meduse

The life cycle ofTripedalia cystophora includes a sessile saclike polyp — the asexual reproducing form — and a pelagic tetraradial medusa — the sexually reproducing generation. Medusan development can be induced by temperature increase. It reveals neither budding nor strobilation, but a real metamorphosis of a polyp to only one medusa. According to morphological and anatomical criteria the metamorphosis can be subdivided into four different stages: (1) four longitudinal furrows segment the polyp, the tentacles of which are apportionated on the four quadrants of the body. (2) The subumbrellar cavity develops by invagination of the peristom; the relicts of the fused tentacles change to four rhopalia buds. (3) Medusan architecture including four new interradial tentacles, four rhopalia and the subumbrellar swimming musculature is completed. (4) A young tetraradial medusa starts swimming. Ultrastructural analysis of those metamorphic stages show the different processes of morphogenesis: (a) Gastrodermal cells — absorptive and spumous cells — undergo transdifferentiation and proliferation to medusan cells of the same structure and function. (b) Epidermal cells, excluding the epithel muscle cells, dissociate and are autolytically withdrawn. Dedifferentiated epithel muscle cells — interstitial cells — regain the ability to develop a complete new set of somatic cells, not originally present in the polyp. They include amongst others cross-striated muscle cells, medusan typic nematocyts and particularly sensory and nervous cells. Those cells establish a nervous system with lens-eyes, simple ocelli, statocysts, diffuse nerve net and an additional nerve ring.     

The role of polarity in the development of the hydrozoan planula larva

Summary These experiments were done in order to define the role that polarity plays during embryogenesis in hydrozoans.Parts of hydrozoan embryos isolated at different developmental stages from early cleavage to postgastrula will regulate to form normal planulae. During this process, the original anterior-posterior axis of the part is conserved. In normal embryos the posterior pole of the anterior-posterior axis is congruent with the site where the polar bodies are given off and with the site where the first cleavage is initiated. By centrifuging fertilized eggs, it is possible to create embryos in which the first cleavage initiation site does not correspond to the site where the polar bodies are given off. In these embryos the posterior pole of the anterior-posterior axis corresponds to the first cleavage initiation site. When parts of these embryos are isolated at different stages they also regulate to form normal planulae. The axial properties of these planulae are determined by the site of first cleavage initiation.The interactions between regions of the embryo with different axial properties were studied by grafting together parts in such a way as to create embryos with abnormal axial arrangements. Following gastrulation interactions take place between the grafted parts leading to the formation of normal planulae with a new set of axial properties.Blastula stage embryos can be dissociated into single cells and the cells can be reaggregated. These reaggregates form normal planulae. Polarity can be entrained in the reaggregates by grafting a small piece of tissue from any part of an intact blastula to the reaggregate. These cells organize the formation of an axis of symmetry with an appropriate orientation with respect to the graft.     

Substratum preferences and planulae settling of two red sea alcyonaceans: Xenia macrospiculata Gohar and Parerythropodium fulvum fulvum (Forskl)

The settling behaviour and substratum preferences of the planulae of the Red Sea soft corals Xenia macrospiculata Gohar and Parerythropodium fulvum fulvum (Forskl) were examined in the laboratory. The planulae of the two species have a short pelagic phase and they tend to settle immediately upon leaving the parent colonies. Mucous secretion is used by the larvae for crawling and adhering to the substratum. They exhibit an aggregated pattern of settlement. The developing polyps are found in depressions or pits of the substratum. The planulae preferentially settle on rough substrata and avoid smooth surfaces. They search for substrata covered with an organic coating, composed of turf or crustose coralline algae. Such substrata create better conditions for larval settlement and metamorphosis. The planulae of P. f. fulvum exhibit a striking preference for upside-down attachment on undersides of the substrata, while Xenia macrospiculata utilizes both substratum faces for settlement. Light intensity seems insignificant in determining attachment sites. The findings of the experiments correspond well with the distributional patterns of juveniles of the two species as found in the natural environment. The specific requirements for settling of both species increase their chances of successful development and thus enhance their survival.     

Identification key for young ephyrae: a first step for early detection of jellyfish blooms

Although jellyfish blooms are a focus of recent research, the roles that the developmental stages of species play are underestimated. Planulae, polyps and ephyrae are inconspicuous and often overlooked. The importance of production of ephyrae from the sessile polyps has become more apparent. Our objective was to establish an identification system for early ephyrae of scyphozoan species in plankton samples. We studied ephyrae of 18 species. Standard measurements were introduced and the variability of marginal lappets analysed. Characters differentiating the 18 species are described. Photographs and drawings of each species are presented as a catalogue of ephyrae of these species. We developed a key for identification of the 18 species.     

A newly discovered oxidant defence system and its involvement in the development of Aurelia aurita (Scyphozoa, Cnidaria): reactive oxygen species and elemental iodine control medusa formation

In Aurelia aurita, applied iodine induces medusa formation (strobilation). This process also occurs when the temperature is lowered. This was found to increase oxidative stress resulting in an increased production of iodine from iodide. One polyp produces several medusae (initially termed ephyrae) starting at the polyp's oral end. The spreading of strobilation down the body column is controlled by a feedback loop: ephyra anlagen decrease the tyrosine content in adjacent polyp tissue by producing melanin from tyrosine. Endogenous tyrosine is able to remove iodine by forming iodiferous tyrosine compounds. The reduced level of tyrosine causes the ephyra-polyp-border to move towards the basal end of the former polyp. We argue that an oxidant defence system may exist which makes use of iodide and tyrosine. Like other marine invertebrates, polyps of Aurelia contain iodide ions. Inevitably produced peroxides oxidise iodide into iodine. The danger to be harmed by iodine is strongly decreased by endogenous tyrosine which reacts with iodine to form iodiferous tyrosine compounds including thyroxin. Both substances together, iodide and tyrosine, form an efficient oxidant defence system which shields the tissue against damage by reactive oxygen species. In the course of evolution (from a species at the basis of the animal kingdom like Aurelia to a highly evolved species like man) the waste product thyroxin (indicating a high metabolic rate) has developed into a hormone which controls the metabolic rate.