Comparison of telomere length among different life cycle stages of the jellyfish Cassiopea andromeda

The polyp (scyphistoma) of the jellyfish Cassiopea andromeda reproduces asexually repeatedly, while the medusa, the sexually reproducing stage, exhibits a relatively shorter life span. As a first step to understand the mechanism behind the differences in the life spans of the polyp and medusa stages of the jellyfish, we compared the lengths of the telomere region of one targeted chromosome between the polyp and medusa stages using a modified single telomere length assay (STELA). The double-stranded regions of the telomeres were amplified by PCR, and the average length of the PCR products was estimated by densitometry analysis of the gel smear. Chromosomes within cells of the bell region of the medusa were characterized by longer telomeres than those of polyps, asexual propagules, or other regions of the medusa. This is the first study to estimate the telomere lengths of targeted chromosomes in a cnidarian and opens a way to understand the mechanism underlying different life spans of the polyp and medusa stages.     

Complex reproductive cycle inEucheilota paradoxica (Hydrozoa: Leptomedusae): Medusae,polyps and frustules produced from medusa stage

Eucheilota paradoxica Mayer, 1900 is a small leptomedusa unknown in the Mediterranean Sea until 1977. Since then, it has become endemic and occurs in great abundance in autumn in the bay of Villefranche-sur-mer. Since no sexual stages have ever been collected, either from the Atlantic Ocean or from the Mediterranean Sea, we decided to investigate the still unknown life cycle of this species. Specimens were obtained in the bay of Villefranche-sur-mer from plankton hauls between 0 and 50 m depth during October and November 1986. At temperatures >18°C, the medusa reproduces intensively by asexual medusal budding (one young medusa liberated per two days). This asexual reproduction explains the rapid proliferation of the species and the origin of the large population every autumn. In cultures maintained at temperatures <18°C, two other reproduction modes, not yet reported in a leptomedusa, were observed: (1) At 16° to 17°C, frustules bud along the canals; these frustules are dormant, giving rise to a small polyp when the temperature increases once more above 18°C. (2) At temperatures close to 15°C each medusa, in place of the gonads, differentiate into one or two polyps; these polyps develop progressively, concomitant with gradual regression of the mother medusa.     

Derivation of the reduced life cycle of <Emphasis Type="Italic">Thecoscyphus zibrowii</Emphasis> Werner, 1984 (Cnidaria,Scyphozoa)

The species Thecoscyphus zibrowii Werner, 1984 has an exceptional life cycle, which lacks a medusa stage but develops an extraordinary structure (egg sac) for reproduction. Investigation of the life cycle, as well as anatomical and histological studies of the different developmental stages of T. zibrowii were performed to provide evidence for a possible homology of the egg sac with the medusa stage and to determine whether the reduced metagenesis of T. zibrowii is derived from strobilation. The egg sac showed several characteristics, which were compared to those of coronate medusae. The ectodermis of the egg sac had a plate-like appearance and was completely ciliated as is typical for coronate medusae. The number and the location of the gonads were similar to those of coronate medusae. The cnidocysts were significantly larger in the egg sac than in the polyp. A size difference of cnidocysts in the medusa and the polyp stage is known for several Coronatae. Characteristics of egg sac formation were compared to characteristics of strobilation. The formation of the early operculum was similar in T. zibrowii and N. eumedusoides. The constriction of egg sac and strobila occurred in the same mode and the gastric cavities of two egg sacs stayed in contact in a similar fashion to the gastric cavities of the strobila discs. The developmental zones of cnidoblasts of the egg sac and polyp were separated during the formation of the egg sac which showed a similar developmental gradient to a strobila. The existence of all of these consistent characteristics makes it very likely that the egg sac structure was homologous to a medusa. The species T. zibrowii would therefore be derived from a metagenetic ancestor. This species has reduced the medusa generation to the greatest extent within the Nausithoidae and has demonstrated thus far the endpoint of a regressive evolution of the medusa generation.     

Life cycle of the jellyfish <Emphasis Type="Italic">Rhizostoma pulmo</Emphasis> (Scyphozoa: Rhizostomeae) and its distribution,seasonality and inter-annual variability along the Catalan coast and the Mar Menor (Spain,NW Mediterranean)

Rhizostoma pulmo is one of the most abundant scyphomedusae along the Mediterranean coasts. To understand changes in the population densities of the medusa stage and its relationship with the benthic stage, we describe all developmental stages from the life cycle of R. pulmo, from the scyphistoma stage to young medusae reared in the laboratory. Mature scyphistomae showed a mean total body length of 1.7 mm and the average tentacle number was 16. Asexual reproduction occurred by lateral budding, podocyst and pedalocyst production. Each strobila released up to 8 ephyrae that had a mean total body diameter of 3.5 mm. Moreover, we also present data on the temporal and spatial distribution of the species in the Catalan Sea and the coastal lagoon on Mar Menor (NW Mediterranean) during the years 2007–2009. In the Catalan Sea, the presence of adult R. pulmo was recorded as extended along the whole coast, but most of the observation was concentrated in the central area; the highest abundances were recorded during the months of July and August. The highest number of observations was detected in 2008 in coincidence with the inter-annual variation observed in the Mar Menor lagoon.     

Polyp and medusa of Dipurena bicircella n. sp. (Hydrozoa: Corynidae) from Northern California

The polyp and medusa of Dipurena bicircella n. sp., a metagenic hydrozoan from Northern California, USA, is described. The arrangement of capitate tentacles of the polyp, in two alternating cycles or circlets, is unique to the genus Dipurena as well as to the family Corynidae. Medusae released in the laboratory attained sexual maturity in 2 weeks. The adult medusa can be distinguished from other medusae of the genus by means of 2 gonad rings, a slight terminal nematocyst cluster on each tentacle, and a relatively small size (about 2 mm in bell height). The polyp was not found in association with sponges, as is the case with some of the other polyps of the genus Dipurena. The medusa is not yet known from the plankton.     

Life cycle of <Emphasis Type="Italic">Carybdea marsupialis</Emphasis> Linnaeus, 1758 (Cubozoa,Carybdeidae) reveals metamorphosis to be a modified strobilation

Two types of metamorphosis occur in the life cycle of Carybdea marsupialis Linnaeus 1758 (Cubozoa, Carybdeidae). In addition to the metamorphosis described several times over, during which the entire polyp transforms into one medusa, we investigated a second type of metamorphosis which leaves a regenerative remnant. This mode of medusa formation seems to be derived from the strobilation known from Scyphozoa. Both types are described and the implications these results have on the idea about the origin of the class Cubozoa, are discussed.     

Life cycle of the rhizostome jellyfish <Emphasis Type="Italic">Rhizostoma octopus</Emphasis> (L.) (Scyphozoa,Rhizostomeae), with studies on cnidocysts and statoliths

Stages in the life cycle of the rhizostome jellyfish Rhizostoma octopus (L.) were reared in the laboratory from planula to young medusa and are described here. Fertilization of eggs was external, and planulae, 110–150 μm in length, appeared after 2 days. These settled and developed into the scyphistoma stage. Scyphistomae reached a maximum size of 2.3 mm, bore up to 24 tentacles, and had a large manubrium. Polyps reproduced asexually mainly by podocysts. Strobilation was induced by temperature change. Each strobila released up to five ephyrae that measured 2.7–5.8 mm in diameter at liberation. During transformation from newly released ephyra to young medusa, velar lappets appeared and increased in number, the manubrium developed eight branched oral arms with epaulettes, and a marginal gastric network arose. Only one cnidocyst type, the “a”-atrichous haploneme, was present in the planula. In addition to these haplonemes, heterotrichous microbasic euryteles were observed in polyps, ephyrae, and medusae. Statoliths, located in the rhopalia, had a characteristic compact shape. These sensory structures increased in number and size with the growth of ephyrae and medusae.     

Invertebrate introductions in marine habitats: two species of hydromedusae (Cnidaria) native to the Black Sea,Maeotias inexspectata and Blackfordia virginica,invade San Francisco Bay

The hydrozoans Maeotias inexspectata Ostroumoff, 1896 and Blackfordia virginica Mayer, 1910, believed to be native to the Black Sea (i.e. Sarmatic) and resident in a variety of estuarine habitats worldwide, were found as introduced species in the Petaluma River and Napa River, California, in 1992 and 1993. These rivers are mostly-estuarine tributaries that flow into north San Francisco Bay. Both species appeared to be well-established in this brackishwater habitat. Salinities at the collection sites were about 11 during the summer, rising to nearly 20 in the early autumn and falling to near 0 in the winter. Large numbers of all sizes of both species of medusae were observed and collected, indicating that the hydroid stages of the life cycles of the two are also well-established in these rivers. In the Petaluma River, populations of both species were at maximum in late July, with numbers of individuals declining through August and into September; the Napa River was sampled only in October, and at that time only B. virginica was found. Examination of full guts of M. inexspectata and B. virginica medusae revealed that both species had fed nearly exclusively on small crustaceans, principally barnacle nauplii, copepods and their eggs and nauplii, and crab zoea larvae (M. inexspectata only). All the M. inexspectata medusae were males, indicating that the population has probably developed from the introduction of perhaps only a single male polyp or polyp bud. In spite of its inability to reproduce sexually, this population appears to be maintained by the prodigious ability of the polyp to bud and reproduce asexually, and is fully capable of invading additional low-salinity habitats from its present Petaluma River site. Male and female B. virginica medusae were collected in both the Petaluma River and the Napa River, indicating that B. virginica may have been introduced by either the polyp or medusa stage (or both), but that multiple individuals (of both sexes) must have arrived from another port in one or more invasions. As indicated for M. inexspectata, the B. virginica population will also probably seed new populations in San Francisco Bay and elsewhere. Based on its cnidome as well as the morphology of both medusa and polyp, M. inexspectata has been reclassified by moving it from the family Olindiidae, Limnomedusae, to the family Moerisiidae, Anthomedusae.     

Life cycle ofRhopilema nomadica: a new immigrant scyphomedusan in the Mediterranean

Rhopilema nomadica is an Indopacific scyphomedusan, which has migrated into the eastern Mediterranean in recent years. Large aggregations of the medusae were recorded in Haifa Bay, Israel, reaching 5.5×10⁵ medusae per square nautical mile during summer 1989. The life cycle ofR. nomadica from planula to young medusa is described. Fertilization is external and planulae are formed within a few hours at 20°C. After settlement, polyps were fed withArtemia sp. nauplii and developed into polydisc strobilae within 45 d. The strobilation process was completed within 7 d, and the liberated ephyrae developed into young medusae within 2 mo. Asexual reproduction occurred mainly via podocyst formation. The population explosion ofR. nomadica could be attributed to its high reproductive potential.     

Release of dissolved organic carbon (DOC) by the scyphozoan jellyfish Aurelia aurita and its potential influence on the production of planktic bacteria

A series of incubation experiments were made to measure the rate of release of dissolved organic carbon (DOC) by the jellyfish Aurelia aurita (L.) (collected in 1991–1992 in Gullmarsfjorden, Sweden). Release of DOC by medusae (9.5 to 18 cm in diameter) from the Skagerrak ranged from 0.70 to 1.6 mg C ind^-1 d^-1 with a mean of 1.2 mg C ind^-1 d^-1 (SD=0.29 mg C ind^-1 d^-1, n=10). Based on data from the literature for two medusa populations, this can be equivalent to 2.5 and 7.1% of the carbon assimilated in one season (June to September). This was similar to the amount of carbon allocated to reproduction. Bacterial abundance was monitored to evaluate the possible stimulating effect of the DOC released. Bacterial growth was stimulated by the presence of A. aurita. The importance of A. aurita as a source of DOC on a large scale is small compared to exudate from primary producers. The volume surrounding each medusa, wherein the DOC released may be enough to sustain a bacterial production such as the one reported from the Swedish west coast, is equivalent to a sphere with a diameter of 0.5 m. Thus, considering the patchy distribution of medusae, the local influence of their DOC release could be important.     

The life cycle ofClytia attenuata (calyptoblastea: Campanulariidae)

The life cycle of the hydroidClytia attenuata (Calkins) (Calyptoblastea: Campanulariidae) has been completed in the laboratory including development of the medusa, previously described asPhialidium lomae Torrey (Leptomedusae: Campanulariidae). Under laboratory conditions, the hydroid exhibits some morphological variation. Characteristic branching of the hydroid occurs at temperatures between 17° to 19°C. At 13° to 15°C the colonies are unbranched and cannot be distinguished fromClytia cylindrica L. Agassiz. Young medusae are similar to other young species ofPhialidium. Development to the adult form requires 25 to 30 days at 17° to 24°C. The adult medusae are 6 to 10 mm in diameter, watch-glass shaped, and have 20 to 28 tentacles. Based on the adult medusa,Clytia attenuata is maintained as a valid species.     

Rate-temperature responses in scyphozoan medusae and polyps

The effects of temperature on oxygen consumption and spontaneous rhythmic activity have been investigated in various stages of the life histories of 3 species of jellyfish from the Chesapeake Bay, USA. All 3 species clearly show the ability to acclimate positively to temperature change. Thermal sensitivity of metabolism in the winter medusa Cyanea capillata fulva is fairly low at temperature intervals which are experienced in nature. Polyps of the two summer medusae, Chrysaora quinquecirrha and Aurelia aurita, show reduced metabolic sensitivity at temperatures normally accompanying high developmental activity and the onset of strobilation.     

Spermatozeugmen und Paarungsverhalten bei Tripedalia cystophora (Cubomedusae)

New observations on the complete life cycle of Tripedalia cystophora Conant have revealed that—because of the radialsymmetrically constructed body of the polyp and its complete metamorphosis into one medusa—the “Cubozoa” are unique in their development, systematics and evolution. the same is true for the sexual biology of their medusae. It has long been known that the female T. cystophora are larviparous; fertilized eggs develop within the gastral pockets into free-swimming planulae. How do spermatozoa approach the eggs inside the female? In laboratory cultures, young medusae could be raised to maturity. Rearing experiments and observations yielded surprising results, revealing a situation which is new for Cnidaria. In T. cystophora, ripe medusae of both sexes can be identified easily by the different colour and structure of the gonads. In the gonads of the ripe male, numerous spermatozoa are joined to form spermatozeugmata of a simple type. Numerous spermatozeugmata form big globular bodies (spermatophores), which develop in small grooves on the inside surface of the stomach. The spermatophores are transferred directly from the male to the female during successive steps of special mating behaviour. The observations confirm that Cubomedusae have reached the peak of medusan specialization.     

Hebella parasitica (Cnidaria,Hydroida): A thecate polyp producing an anthomedusa

The thecate hydroid Hebella parasitica (Ciamician), reared under controlled conditions, produced an ephemerous medusa with gonads on the manubrium. This feature does not agree with the current classification of hydroids, according to which a thecate polyp is expected to produce a medusa with gonads on its radial canals. As no data on the reproduction of other species of Hebella are available, the systematic position of H. parasitica should be considered uncertain.Work done within the Finalized Project Oceanografia e i fondi marini, sub-project Risorse biologiche of the C.N.R.     

Periods of non-feeding in Polysyncraton lacazei (Ascidiacea: Didemnidae): a rejuvenative process?

Polysyncraton lacazei (Giard) (Ascidiacea: Didemnidae) displays short periods of non-feeding during the warm season in the northwestern Mediterranean Sea (NE of Spain). These periods were analyzed from 1988 to 1990 by monitoring naturally occurring colonies and by morphological and histological observation of non-feeding colonies. During this phase the surface of the colonies is covered by a glassy pellicle and the siphonal apertures are sealed. The phenomenon consists of a reabsorption of the branchial portion of the zooids and a budding of new thoraces. This process does not fit into either the propagative or survival categories of budding proposed for ascidians, and is interpreted as a rejuvenative phenomenon which extends the life span of the zooids.     

The life cycle of the commensal hydromedusa Eutima sapinhoa n. sp.

Eutima sapinhoa n. sp. is a small hydroid, which lives attached by a basal disc to the mantle, foot, gills and labial palps of the bivalve Tivela mactroides (Born, 1778), found on the northern littoral of São Paulo State, Brazil. This bivalve, locally known as “sapinhoá”, is used as food by the coastal inhabitants. The hydroid produces a leptomedusa which belongs to the family Eutimidae. The medusa bud develops as a small knob-like protuberance near the base of the polyp and, after 61/2 days, reaches the free-swimming stage in covered preparation dishes containing about 200-ml filtered sea water at a temperature of 20° to 22°C. After 25 days the medusa is 4 mm high, 4-mm in diameter, and possesses 4 radial tentacles —each about 2 to 3 times as long as the bell diameter, 8 marginal vesicles — 2 in each quadrant, and 28 small marginal swellings — 7 in each quadrant. The peduncle is as long as the height of the bell, 4 single long gonads develop on the subumbrella on each radial canal. The nematocysts are small atrichous isorhizae, with capsules averaging 7 μm in length.     

Temperature,salinity, and prey effects on polyp versus medusa bud production by the invasive hydrozoan<Emphasis Type="Italic"> Moerisia lyonsi</Emphasis>

Hydrozoan species are renowned for flexible asexual reproduction, which may predispose them to be successful invaders. Polyps of the invasive hydrozoan Moerisia lyonsi (Boulenger, 1908) have very high rates of asexual production of both polyp and medusa buds. In order to determine how environmental factors affect asexual reproduction in M. lyonsi, the quantitative relationships between polyp bud and medusa bud production were studied in a 31-day laboratory experiment during August 2001. The combined effects of prey (4, 8, 12, 16 Acartia tonsa copepods polyp^–1 day^–1), temperature (20°C, 29°C), and salinity (5, 15, 25) were tested on the development times for polyp buds (DT_p) and medusa buds (DT_m), the total asexual reproduction rate (ARR, no. buds polyp^–1 day^–1), and the ratio of medusa bud to total bud production (R_m). Greater food consumption significantly and directly enhanced ARR and R_m and shortened DT_p and DT_m. A lower temperature (20°C) and higher salinity (25) reduced food consumption, lengthened development times, and decreased ARR and R_m, with opposite effects for the higher temperature (29°C) and lowest salinity (5). The patterns of variation of these reproductive parameters are more complex. DT_m was most sensitive and was significantly and directly affected by all three measured factors. In addition to food consumption, direct effects were seen by temperature on DT_p and by salinity on R_m. ARR was directly affected only by food consumption. Overall, DT_p, DT_m, and R_m were more sensitive to environmental differences than was ARR. More favorable conditions enhanced medusa bud production. The adaptive reproductive processes and their significance for the maintenance and dispersal of M. lyonsi are discussed.Communicated by J.P. Grassle, New Brunswick     

Substrate choice and settlement preferences of planula larvae of five Scyphozoa (Cnidaria) from German Bight,North Sea

The settlement behaviour of planula larvae and their development to young polyps was investigated in laboratory experiments in five scyphozoan species [Aurelia aurita (L.), Cyanea capillata (L.), Cyanea lamarckii Péron and Leseur, Chrysaora hysoscella (L.), and Rhizostoma octopus (L.)]. The undersides of settling plates were strongly preferred for settlement. Shells, the only natural substrate type offered, were less attractive than artificial substrates (concrete, machined wood, polyethylene, and glass). The advantages of colonization of substrate undersides for survival and reproduction of polyps are discussed. It is supposed that the increase of artificial substrates in our seas, due to marine litter pollution and submarine building activities, enlarge the areas of distribution of scyphozoan polyps, in coastal as well as in off-shore regions. Subsequent increases in ephyra production by polyps are probably one reason for the increase in mass occurrences of jellyfish recognized worldwide during the last few decades. It is suggested that the early developmental stages in the cnidarian life cycle, the planula larvae, and the polyps, play the key role in the development of jellyfish outbursts.