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.     

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.     

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.     

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.     

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.     

Quantification of sexual reproduction in the marine benthic hydroid Campanularia everta

Campanularia everta is an epiphytic hydroid that may form dense populations on the macroalga Halimeda tuna. The main objects of this study were to quantify sexual reporduction and estimate sexual reproductive output of this hydroid. Sexual reproduction occurred from mid-October to mid-December 1991 along the Spanish Mediterranean coast. During this period, male and female colonies formed gonangia. Four oocytes mature in each female gonangium, and embryonic development starts probably after internal fertilization occurs. Planulae complete their development within a mucus sheath attached to the top of the gonotheca (acrocyst). Eight successive gonangia with a life-span of 1 wk each were formed over a 2 mo period. The fertile period was characterized by high initial production of gonangia followed by a progressive decline resulting from a decrease both in the number of fertile colonies and in the gonangia density of fertile colonies. Annual production was estimated at 42000 gonangia m^-2, representing 83000 oocytes m^-2. The high fertilization rates observed (77 to 100%) yielded a minimum production of 64000 planulae m^-2. Reproduction in C. everta is characterized by: (1) a high number of larvae produced m^-2; (2) formation and gradual release of larvae throughout the sexual reproduction period; (3) direct formation of planulae with no intermediate medusa stage; (4) low dispersive ability of the planula. All these mechanisms are part of a reproductive strategy designed to ensure the permanence of the population in its habitat.     

Laboratory study of predation by Aurelia aurita on larvae of cod,flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.     

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.     

Microalgal communities epibiontic on the marine hydroid <Emphasis Type="Italic">Eudendrium racemosum</Emphasis> in the Ligurian Sea during an annual cycle

The microalgal community associated with Eudendrium racemosum, a marine hydroid widely distributed in the Mediterranean Sea, was studied during an annual cycle, at monthly frequency, in a coastal station of the Ligurian Sea. Microalgae were represented mainly by diatoms, which exhibited higher abundance and biomass values between autumn and spring (max 46,752 cells mm⁻² and 1.94 μg C mm⁻², respectively), while during summer a significant decrease was observed (min 917 cells mm⁻² and 0.013 μg C mm⁻²). High levels of abundance of filamentous cyanobacteria were observed in summer. Spatial distribution of epibiontic microalgae showed a markedly increasing gradient from the basal to the apical part of hydroid colonies. Considering the growth forms of diatom communities, motile diatoms (mainly small naviculoid taxa) were the most abundant in all the periods. Adnate (Amphora and Cocconeis spp.) were distributed mainly in the basal and central part of hydroid colonies and showed two peaks (autumn and summer). Erect forms (mainly Tabularia tabulata, Licmophora spp., Cyclophora tenuis) were mainly distributed in the apical part of the colonies and showed their maximum densities in spring–summer. Tube-dwelling (Berkeleya rutilans, Parlibellus sp.) were observed at low densities throughout the study period, without any significant temporal or spatial variability. Comparing the microalgal communities on marine hydroid to those grown on mimic substrata placed in the sampling station during summer, significantly higher values of abundance were observed in the hydroid, suggesting that microalgae may benefit from the polyp catabolites. This fact was particularly evident for the adnate diatoms, whose temporal trend paralleled the cycle of hydroid host.     

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.     

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.     

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.     

Ecology of the bivalve-inhabiting hydroid Eugymnanthea inquilina in the coastal sounds of Taranto (Ionian Sea,SE Italy)

The life history of the bivalve-inhabiting hydroid Eugymnanthea inquilina was investigated in two different hosts, the mussel Mytilus galloprovincialis (collected from 1989–1991 from the Ionian Sea, Italy) and the clam Ruditapes decussatus (collected from 1991–1992, Ionian Sea, Italy). Hydroids living in mussels revealed a size selection for hosts longer than 40 mm, being almost completely absent in mussels below this size. This might be controlled by signals linked to the sexual maturity of the bivalve. The proportion of molluscs inhabited showed a seasonal trend in mussels only, with a sharp decline at the onset of medusoid liberation. Production of medusoids was high in mussels, whereas medusoids were rare and often abortive in clams. This indicates a higher degree of fitness of E. inquilina in mussels than in clams. The hydroid life cycle was not completed in clams, which therefore were presumably supplied by planulae from medusoids produced by mussel-inhabiting hydroids. Mussels played a key role in the stability and persistence of E. inquilina populations in the studied area. Selective ingestion of trematode sporocysts by E. inquilina hydroids indicated a protective role of the hydroid against mussel parasites, leading to reconsideration of this symbiotic association as a possible mutualism rather than a simple inquilinism.     

<Emphasis Type="Italic">Tiburonia granrojo</Emphasis> n. sp., a mesopelagic scyphomedusa from the Pacific Ocean representing the type of a new subfamily (class Scyphozoa: order Semaeostomeae: family Ulmaridae: subfamily Tiburoniinae subfam. nov.)

Submersible observations off Japan, Hawaii, and California, USA, at depths of 645–1497 m, have revealed a previously undescribed species of large semaeostome scyphomedusa. These observations were made from 1993 to 2002. The medusa, Tiburonia granrojo n. sp. is sufficiently different from other species in the family Ulmariidae to justify the creation of a new subfamily (Tiburoniinae). This subfamily and species are distinct in overall bell morphology and color, lacking any marginal tentacles, and having four to seven short, thick oral arms that extend beyond the bell margin. The entire medusa, including the mesoglea, is a deep red. A new key to the subfamilies of the Ulmaridae and large subunit rRNA sequence information for T. granrojo are provided. That new species of this size and mass are still being discovered in the deep waters of the world suggests that deep-water species remain undescribed. Additional information is available at http://www.mbari.org/midwater     

Detection of the thraustochytrid protist Ulkania visurgensis in a hydroid,using immunofluorescence

An immunofluorescence technique was employed to detect the thraustochytrid protist Ulkenia visurgensis (Ulken) Gaertner, originally isolated from an algal bed, in natural samples in Goa, India. Collections were made monthly from September 1985 to November 1986. By treating the samples with antiserum prepared against this organism and conjugated with FITC stain, the protist was regularly found to occur in association with a hydroid. Several cells of the organism were observed in the coelenteron and the hydranth of the hydroid. The thraustochytrid could be repeatedly isolated in cultures from the hydroid. The cells of the protist differed from those in culture in that they lacked ectoplasmic net elements.     

To what extent does upright sessile epifauna affect benthic biodiversity and community composition?

Small-scale habitat complexity, including that caused by biological structures, is an important factor in structuring benthic communities and also sometimes in increasing biodiversity. The aim of this study was to determine if hydroid colonies have an effect on the composition of benthic communities in the Irish Sea, and if so, which components of the fauna are affected. Forty-six seabed core samples were taken by divers from two sites off Port Erin, Isle of Man, Irish Sea. Half of these were centred on hydroid colonies, half were not. All taxa retained by a 63-m sieve from the cores were identified and counted. Community composition and diversity were compared between hydroid and non-hydroid cores using multivariate and univariate methods. Benthic communities were significantly different between the two sample groups. This was almost entirely due to the presence of sessile and mobile epifaunal taxa in the hydroid cores. The tube-building amphipod, Ericthonius punctatus, was particularly abundant attached to the hydroid stems. Infauna was not significantly different between the two groups. Upright sessile epifauna may play a particularly important role in the Irish Sea as a settlement substrate for juvenile scallops (Pecten maximus and Aequipecten opercularis), which are an important fishery resource in this area. The 11-year closure of an area to dredging has not only enhanced scallop stocks but has had the added benefit of enhancing habitat complexity and biodiversity.Communicated by J.P. Thorpe, Port Erin