Young Medusae Research Articles

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.

Ultrastructural observations on prey capture and digestion in the scyphomedusa Aurelia aurita

Aurelia aurita medusae are able to catch their prey with their entire body surface. Catch efficiency in medusae caught in Kiel harbour in May 1985 was found to be highest at the tentacles and lowest at the subumbrella. Surface structures of the medusa as well as the cnidom are described by SEM observations. Microbasic heterotrichous euryteles and atrichous isorhizas were found. Discharged nematocysts on the prey's skin indicate different functions of the two types. The villi in the gastral cavity show a characteristic morphological differentiation that consists of a ciliated distal and a basal area covered by vesicles. Four types of glandular cells were identified by TEM observations. Mucous cell types preferably occur in densely ciliated areas. The presence of serous cells is restricted to the basal region of the gastral villi and gastral cavity where the extracellular predigestion takes place. The time of food passage in young medusae of A. aurita decreases from 19 h at 4°C to 4 h at 22°C.

Cytological changes during the metamorphosis from the cubopolypTripedalia cystophora (Cubozoa, Carybdeidae) to a medusa

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 Reproductive Ground of the Common Jelly-fish, Aurelia aurita, in Urazoko Bay, Fukui Prefecture

In spite of the world-wide distribution and common occurrence of Aurelia aurita, the details of its reproductive ground have little been given. A series of work to make the reproductive ground of this medusa clear was carried out in Urazoko Bay, a small inlet, situated in the eastern part of Wakasa Bay on the Japan Sea coast, in the period from November 1970 through April 1973.The occurrence patterns of early liberated ephyrae, metephyrae and young medusae at their maximum season were respectively checked by examining the samples collected by means of vertical hauls of a plankton-net (45cm in mouth diameter and 0.33mm in mesh szie) at each of the stations settled in the bay (Fig. 1). The settlements of planulae and early polyps were examined by monthly observations throughout the breeding season from late November 1970 through July 1971, using the collectors made of five upper shells of Pecten albicans and hung at the depth of 0, 2, 5 and 10 meters (Fig. 3) from the rafts which were set at each of the stations in the bay (Fig. 2). The results obtained are summarized as follows:1) Early ephyrae were mainly distributed in the inner part of the inlet or the coastal shallow areas of the waters (Figs. 4 and 5).2) Planulae and early polyps were found on the collectors in the inner part of the bay from January to June, most abundantly between the surface and 5 meter layer (Fig. 6).3) According to these results and the distribution patterns of marine plants in the bay, it will be concluded that the reproductive ground of this medusa in the bay is the areas that are covered with marine plants such as Sargassum and Zostera (Figs. 8 and 9).

On Pelagiana trichodesmiae n.gen., n.sp., family Pandeidae, (Anthomedusae/Athecatae, Cnidaria), a new hydrozoan associated with the planktonic cyanophyte Trichodesmium thiebautii

A new athecate hydroid and its young medusa are described, the hydranths of which are commonly found embedded in colonies of the planktonic blue-green alga Trichodesmium thiebautii Gomont in the tropical and subtropical Atlantic. The hydroid and its medusa, named Pelagiana trichodesmiae n.gen., n.sp., are placed tentatively in the family Pandeidae (order Anthomedusae/Athecatae) because of the structure of the medusa and the one circle of filiform tentacles on the hydroid. The medusa is known only from one specimen which was 0.3 mm wide and 0.4 mm high immediately after release. It is deep bell shaped with a stomach one-third of the subumbrella and two marginal tentacles with large triangular marginal bulbs.

Notes on Stauridiosarsia producta (Hydrozoa, Corynidae), a New Addition to the New England Marine Fauna1

The hydroid and medusa of Stauridiosarsia producta (Wright, 1858) are reported for the first time from the New England coast of North America. The laboratory reared hydroid exhibits variation encompassing the previously reported forms from England and Helgoland. Nematocysts of the hydroid are stenoteles of two sizes. Young medusae have nematocysts irregularly scattered over the exumbrella. These are lost after 5–7 days. The characteristic umbilical canal of the medusa becomes distinct about 24 hours after liberation. Development to sexual maturity requires about 30 days. In addition to the two sizes of stenoteles, the medusa also possesses desmonemes.

Laboratory observations on the life history of Rhopilema verrilli (Scyphozoa: Rhizostomeae)

The life history of the scyphozoan Rhopilema verrilli is described from the planula to the young medusa stages. Planulae are retained within the gonadal tissue of the medusa until fully developed. On liberation, most planulae set and developed into small scyphistomae within 7 to 10 days. The scyphistoma differs from those of other described species in having an unusually large, clavate manubrium. The only means of asexual reproduction observed in the scyphistoma cultures involved the formation of podocysts. Strobilation was usually of the monodisc variety, although polydics strobilation was not infrequent. The process of strobilation was completed within 7 days at 20°C. Newly liberated ephyrae typically had 8 pairs of lappets, and 8 rhopalia. Ephyral development resembled that of the closely related rhizostome Rhizostoma pulmo. The cnidome of the planula and scyphistoma consisted of atrichous isorhizas (“a” atrichs) and microbasic heterotrichous euryteles, while that of the strobila and ephyra consisted of “a” atrichs, euryteles, and holotrichous haplonemes

福井県浦底湾におけるミズクラゲの生態-IV

So far as we know, very few reports are available on the year-round growth of the jelly-fish, Aurelia aurita (LINNE), excepting for reports confined to partial or limited seasons. In continued studies on the ecology of the Aurelia aurita in Urazoko Bay, a small inlet of the Wakasa Bay on the south-western coast of the Japan Sea, the author was able to collect fairly sufficient data on the monthly changes in the bell-length composition of this Scyphomedusa, enough to discuss its breeding season, growth and longevity. Field sampling was carried out every month by vertical and horizontal hauls with two types of plankton-nets (100cm in mouth aperture, 2mm in mesh and 45cm in mouth aperture 0.33mm in mesh) and also hand-nets (40×20cm opening, 2mm in mesh), together with hydrographic observations throughout the period from April 1969 to April 1970. About 3, 600 individuals of the medusae were collected and their bell diameter was measured while alive. Also the condition of the fertilized eggs or planula larvae attached to the oral-arms or subumbrella was simultaneously checked. The results obtained are summarized as follows: 1) From monthly changes in the bell-length composition, season of appearance of planula and also from the results of the previous reports, the longevity of Aurelia aurita was supposed to be from more than one year to less than two years (Fig. 1). 2) A number of young medusae which appeared in May or June were 1cm in bell-length, 0.2 to 0.9 in body weight. Their growth was most rapid in summer (July to August) and spring (March to April). They attained 22cm in bell-length and 400 g in body weight in 11 months. 3) A close correlation was observed between the increase in bell-length or body weight and the seasonal change in water temperature. 4) The fertilized eggs or planulae were observed from January to June in water temperature of 8 to 19°C and its peak from January to May with temperature of 8 to 18°C. 5) The medusae with fertilized eggs or planulae ranged from 7 to 31cm in bell diameter.

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 lomaeTorrey (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 cylindricaL. 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.

HYDROID AND YOUNG MEDUSA STAGES OFDIPURENA STRANGULATA(HYDROZOA, CORYNIDAE)

The hydroid stage in the life history of Dipurena strangulata, a relatively well-known medusa along the United States east coast, is described for the first time. A previous description of the young medusa does not accord with observations recorded here, but is similar to and may have been based on young Linvillea agassizi rather than D. strangulata. Of the described hydroids of Dipurena, D. strangulata is most like D. reesi morphologically, but differs in the position of the filiform tentacles and the number of endodermal cells in the capitate tentacles. The status of the various species of Dipurena described from the North American Atlantic coast is reviewed.

A commensalic hydroid from wood-boring molluscs

Summary The occurrence of a commensalic hydroid of the genus Eugymnanthea has been noted in the wood-boring molluscs such as Nausitora hedleyi, Teredo furcifera and Martesia striata. Both the polyp and the young medusa are described. The mode of formation of the colony, movements of the hydroid and preliminary observations on the general ecology are noted and the nature of the relationship indicated.

Hydroid generation and developmental history ofEucheilota maculata (Thecata — Leptomedusae). With a contribution to the methods of culturing marine hydroids

Polyps and medusae differ in regard to habitats, evolution, and morphological structures. In order to replace the former taxonomic systems which deal with polyp and medusa generations separately, by a single valid classification including both generations, knowledge of all essential life history phases is necessary. Modern methods of culturing marine hydroids are outlined briefly. Successful culturing provides the means to link formerly unidentified polyps or medusae with one another. The present paper is concerned with the hydroidEucheilota maculata Hartlaub, the medusa of which is common in the southern North Sea. The polyps formerly unknown have been reared from fertilized eggs of the medusae. They were raised to full size, formed colonies, and produced gonangia and medusae. Thus the morphology of the single polyp, the polyp colony, and of the young medusa could be investigated in detail. The nematocyst equipment of the two generations and of all developmental stages is described as well as the number of chromosomes. The systematic position of the genusEucheilota is discussed and the diagnosis of the speciesE. maculata, including the two generations, given.

A calycopsid medusa from the Firth of Clyde

Anthomedusae of the family Calycopsidae are in general oceanic in distribution. The only species recorded from British waters isBythotiara murrayiGünther, reported from fairly deep water far offshore from the west and southwest coasts of Ireland. Its early stages have been unknown. A very young medusa caught at the surface in the Firth of Clyde has been reared through several stages, which are described and figured. It is considered to be a young B.murrayi.

Hydramoeba hydroxena (Entz), a Parasite on the Fresh‐water Medusa, Craspedacusta sowerbii Lankester, and its Pathogenicity for Hydra cauliculata Hyman

SYNOPSIS.An amoeba found on the fresh‐water medusa, Craspedacusta sowerbii Lankester, collected in the Southampton Quarry Pond at Richmond, Virginia, is described and found to be identical with Hydramoeba hydroxena (Entz) which occurs on various species of fresh‐water hydras. Transfer of the amoeba to Hydra cauliculata Hyman, and other experiments, show it to be a facultative parasite for this species. The pathogenicity of the amoeba is decreased by fouling of the culture medium; the resistance of the hydra is decreased by starvation. Hydramoeba is also capable of destroying adult fresh‐water medusae in six days. Its relation to young medusae is not known, but the amoeba apparently does not attack the polyps or other developmental stages.

The Hydroid of the Medusa Dipurena Halterata (Forbes)

Although the medusa Dipurena halterata (Forbes, 1846) is well known, and has been figured by a number of authors (e.g. Forbes, 1848; Browne, 1897), the hydroid of this peculiar species has remained unknown. This medusa is rather scarce at Plymouth (Russell, 1938). On May 3 1938 I had the good fortune to find at Plymouth a small hydroid of the Syncoryne type which later liberated young medusae, and these proved to be young specimens of Dipurena halterata.

Observations on British and Norwegian Hydroids and Their Medusae

The newly liberated medusa of Perigonimus muscoides M. Sars has been found to be a Bougainvillia. A specimen from the plankton points to the extreme probability that it can be regarded as synonymous with a previously described medusa, B. nordgaardi (Browne). The name of both hydroid and medusa now becomes B. muscoides (M. Sars 1846).The systematic importance of the above discovery is discussed, and the genus Rhizorhagium M. Sars 1877 is redefined to include all those species of “Perigonimus” with fixed gonophores, viz. Rhizorhagium roseum, R. sarsi, R. antarcticum, R. formosum, and a new species, R. album, from the Cornish coast.Variations in the form of the hydroid of Leuckartiara octona are described. The newly liberated medusa of Perigonimus abyssi G. O. Sars is figured for the first time and the species referred to the genus Leuckartiara.A new Bimeria-like hydroid, Thamnostoma russelli, is described. The characters of the medusa indicate that it belongs to the genus Thamnostoma Haeckel, and the characters of the hydroid show that the genera Thamnitis and Thamnostoma must be united.Corymorpha annulicornis M. Sars is redescribed from living specimens and the medusa is shown to be Euphysa aurata Forbes. It must henceforth be known as Corymorpha aurata (Forbes).A new species of Campanulina, C. paracuminata, with its young medusa is described from Plymouth.Notes are included on Boreohydra simplex, Stauridium productum and Staurocoryne filiformis.Certain points in the synonymy of all these species are discussed.

On Rearing the Hydroids of Certain Medusae, with an Account of the Methods Used

The development of the hydroid of Amphinema dinema (Peron &amp; Lesueur) has been followed in the laboratory until the production of young medusae and the hydroid identified as Perigonimus serpens Allman.The hydroid of Amphinema rugosum (Mayer) is described for the first time. It is very similar to P. serpens but more robust.The hydroid has been reared from Rathkea octopunctata (Sars); it is very minute and the hydranths possess a single whorl of long filiform tentacles/A small Cuspidella hydroid was reared from Mitrocomella brownei (Kramp).Certain points in the synonymy of these species are discussed. An account of the methods of rearing used is also given.