Evolution and taxonomy in capitate hydroids and medusae (Cnidaria: Hydrozoa)

A cladistic analysis of Capitata groups the families in four suborders based on medusa characters (such as manubrium morphology, position of gonads, and position and number of marginal tentacles) and hydroid characters (such as presence or absence of an oral tentacle whorl, and the different development of the tentacles of the oral and aboral whorls). On the family and generic levels, the revision results in changes which unite the separate hydroid and medusa taxonomic systems, defining genera which are not based on characters solely relating to the reduction of medusae to fixed gonophores. In those families where the reduction of the medusa can be analysed, it is shown that the reduction occurred after all synapomorphies defining the genera had evolved and usually affected individual species within a genus rather than the original species from which the other species in the genus evolved. This supports the view that medusa reduction is not in itself a valid generic character. A discussion of the theories of 'inconsistent' or 'mosaic' evolution concludes that no difference in evolutionary rate or degree of specialization can be demonstrated among taxa with free medusae and taxa with gonophores.     

拟柄突和平水母在中国的首次发现及其生活史观察

报道青岛海洋科技馆培养的和平水母属(软水母亚纲,和平水母科)一种我国的新纪录--拟柄突和平水母西 Eirene lacteoides Kubota and Horita,1992.首次提供该种水母水螅体的形态,并对各期水母体的特征进行描述,为编写水螅水母动物志提供参考.     

The life cycle of Hydrichthys tnirus (Gnidaria: Hydrozoa: Anthomedusae: Pandeidae)

The previously unknown life cycle of the parasitic hydroid Hydrichthys mirus is described. The adult medusa has 5–6 tentacles and could be referred to Leuckartiara. Another species of Hydrichthys has previously been shown to have a Stomotoca -like medusa, characterized by the possession of two tentacles. It is proposed that Hydrichthys originated from the Leuckartiara lineage and that, through paedomorphosis in at least one species, the medusa retained the two-tentacle state of the newly-released medusa of all pandeids, thus becoming referable to Stomotoca. It is suggested that Stomotoca has hitherto constituted a polyphyletic taxon, embracing parallel lineages of pandeids, each retaining juvenile features. An additional genus, Larsonia , is introduced to accommodate species with Stomotoca-like medusae and Hydrichthys -like hydroids.     

Advanced Cambrian hydroid fossils (Cnidaria: Hydrozoa) extend the medusozoan evolutionary history

Primitive cnidarians are crucial for elucidating the early evolution of metazoan body plans and life histories in the late Neoproterozoic and Palaeozoic. The highest complexity of both evolutionary aspects within cnidarians is found in extant hydrozoans. Many colonial hydrozoans coated with chitinous exoskeletons have the potential to form fossils; however, only a few fossils possibly representing hydroids have been reported, which still require scrutiny. Here, we present an exceptionally well-preserved hydroid found in the Upper Cambrian Fengshan Formation in northern China. It was originally interpreted as a problematic graptolite with an uncertain systematic position. Based on three characteristic morphological traits shared with extant hydroids (with paired hydrothecae, regular hydrocaulus internodes and special intrathecal origin pattern of hydrocladium), we propose this fossil hydroid as a new genus, Palaeodiphasia gen. nov., affiliated with the advanced monophyletic hydrozoan clade Macrocolonia typically showing loss of the medusa stage. More Macrocolonia fossils reviewed here indicate that this life strategy of medusa loss has been achieved already as early as the Middle Devonian. The early stratigraphical appearance of such advanced hydroid contrasts with previous molecular hypotheses regarding the timing of medusozoan evolution, and may be indicative for understanding the Ediacaran cnidarian radiation.     

The Medusa of Velella velella (Linnaeus, 1758) (Hydrozoa, Chondrophorae)

A mature medusa of Velella velella (Linnaeus, 1758) is reportedfor the first time from the North Atlantic; previously adultmedusae were known only from the Mediterranean. This specimen,collected by SCUBA divers, is the largest specimen recordedto date. Distinctive features are: two opposite adaxial-axialpairs of perradial capitate tentacles; two marginal bulbs lackingtentacles; conical manubrium with 4 perradial longitudinal gonads;perradial exumbrellar cnidae tracts; cnidome of stenoteles andmacrobasic euryteles; and zooxanthellae within the subumbrella.Since this specimen was collected near the surface and has zooxanthellae,it is likely that V. velella medusae are epipelagic.     

Redescription of Laomedea exigua M. Sars, a hydroid new to Scandinavia, with comments on its nematocysts, life cycle and feeding movements

The little-known hydroid Laomedea exigua M. Sars, 1857, is recorded for the first time from Scandinavian waters. The species is redescribed and the life cycle, lacking a medusa stage, is confirmed by rearing. The nematocysts are diagnostic of the species. Tentacles and hypostome co-operate in capturing prey.     

Temporally and spatially restricted expression of a gland cell gene during regeneration and in vitro transdifferentiation in the hydrozoan Podocoryne carnea

An antiserum to transdifferentiated striated muscle cells from the medusa of Podocoryne carnea was prepared and used to screen a gt11-expression library prepared from gonozoids of P. carnea. We isolated a cDNA clone termed Pod-EPPT with at least 63 tandem repeats of the tetrapeptide-motive glu-pro-pro-thr, named Pod-EPPT. Using Pod-EPPT as a molecular marker for head quality the morphological relationship between the two metagenic life stages of this hydroid, the polyp and the medusa, was studied. In situ hybridization demonstrated that expression of the gene corresponding is restricted to secretory cells in the endoderm of the oral hypostome region of polyps and medusae and, presumably, to progenitor cells of this type. Cells expressing Pod-EPPT could not be observed in the larval stage. During head regeneration in polyps, Pod-EPPT expression is upregulated soon after head removal in previously non-expressing cells and in newly differentiating secretory cells. This activation of a head-specific gene precedes the morphologically obvious events of head regeneration. Pod-EPPT is one of the genes that are activated during manubrium (mouth) regeneration from experimentally combined subumbrellar plate endoderm and striated muscle of the medusa.     

Nematocysts of the Mediterranean hydroid Halocordyle disticha

The morphology, distribution and function of nematocysts in the hydroid Halocordyle disticha were studied by light and scanning electron microscopy. Two types of stenoteles, two types of microbasic b-mastigophores (one with a capsular inclusion) and one type of desmoneme were identified. Prey-capturing experiments were performed with Artemia sp. nauplii. Stenoteles and microbasic mastigophores (those with inclusions) penetrated and paralyzed Artemia larvae, whereas desmonemes kept them in a firm grip by winding around setae.     

Larval behavioral,morphological changes,and nematocyte dynamics during settlement of actinulae of Tubularia mesembryanthemum,Allman 1871 (Hydrozoa: Tubulariidae)

The marine colonial hydroid Tubularia mesembryanthemum produces a morphologically unique dispersive stage, the actinula larva. Detailed observations were made on the behaviors and nematocyte dynamics of actinula larvae during attachment and morphogenesis by employing microscopic and time lapse video techniques. These observations produced four primary results. (1) Actinula larvae demonstrated two forms of attachment: temporary attachment by atrichous isorhiza (AI)-nematocysts discharged from the aboral tentacle (AT) tips-and permanent settlement by cement secretion from the columnar gland cells of the basal protrusion. (2) During larval settlement, numerous AIs were discharged from the AT tips with sinuous movement and rubbing of the tentacles onto the substrata, leading to "nematocyte-printing" around the settlement site. (3) Simultaneous with the discharge of the AIs, migration of stenoteles, desmonemes, and microbasic mastigophores occurred, resulting in a dramatic change of nematocyte composition in the ATs after larval settlement. This was in parallel with changes in larval behavior and the tentacle function. (4) Nematocyte-printing behavior during settlement could be recognized as metamorphic behavior responsible for irreversible changes in AT function, from attachment to feeding and defense.     

Larval necrophilia: the odd life cycle of a pandeid hydrozoan in the Weddell Sea shelf

Colonies of an athecate hydroid were found at six stations in the high Antarctic (Weddell Sea) growing on dead specimens of Flabelligera mundata (Annelida, Polychaeta). All living specimens of F. mundata at the same stations were free of epibionts. Transplantation experiments showed that hydropolyps did not produce stolons on substrates other than the epidermal jelly coat and chetae of dead F. mundata specimens. The largest colonies (>1,000 polyps) producing medusa buds were cultured until medusa liberation: growth of medusae was then surveyed for the next 5 weeks, but development of adult features was extremely slow. Young medusae were ascribed to the suborder Pandeida by the presence of two main characters, namely (1) hollow marginal tentacles, and (2) a mouth with four simple lips. Considering polyp and young medusa features, this species is acknowledged as newly recorded for the Southern Ocean, and assigned to the genus Neoturris (Hydroidomedusae, Pandeidae).     

FMRF-amide immunoreactivity pattern in the planula and colony of the hydroid Gonothyraea loveni

Gonothyraea loveni (Allman, 1859) is a colonial thecate hydrozoan with a life cycle that lacks a free-swimming medusa stage. The development from zygote to planula occurs within meconidia attached to the female colony. The planula metamorphosis results in the formation of a primary hydranth. The colony then grows by development of new colony elements. In the present work, we studied the temporal pattern of the formation of FMRF-amide-positive cells during embryogenesis, in larvae and during early colony ontogeny. FMRF-amide-positive cells appear in the planula only after its maturation. However, they disappear after planula settlement. For the first time, we show that neural cells are present in the coenosarc of the hydroid colony. We also trace the process of neural net formation during the development of a new shoot internode of the G. loveni colony.     

The development of cnidarian stinging cells: maturation and migration of stenoteles of Hydra vulgaris

The late stages of stenotele development and the migration and installation of freshly matured stenoteles in Hydra have been studied by kinetic and immunofluorescence investigations with rhodamine-labelled polyps. It was found that the high concentration of osmotic pressure-generating poly(-glutamic acid)s is synthesised exclusively within the lumen of the immature nematocyst. Assembly of the polymers, which is completed after approximately 0.5 days, is accompanied by a swelling of the capsule and ends when the cyst is mature. Active migration of the stenoteles to the tentacles begins only about 1.0 day later, and the time required for installation of a stenotele on the outer surface of the tissue amounts to about another 1.5 days. Furthermore, the results obtained suggest that the disintegration of the clusters of growing stenoteles, which begins 0.5 to 1.0 days before maturation, is a passive process; the ability of a nematocyte to migrate actively to the tentacles is acquired after maturation and might be controlled directly by regulating factors contained in the tissue.Abbreviations BrdU 5-bromo-2-deoxy-uridine - BSA bovine serum albumine - DIC differential-interference contrast - DTE 1,4-dithioerythritol - FITC fluoresceinisothiocyanate - MBS m-maleimidobenzoyl-n-hydroxysuccinimide ester - PBS phosphate-buffered saline - PEG poly(ethylene glycol) - p/GA poly(a/y-glutamic acid) - TRITC tetramethyl-rhodamine6-isothiocyanate - TROMI tetramethyl-rhodamine-5/6-maleimide     

Reproduction of the colonial hydroid Obelia geniculata (L., 1758) (Cnidaria,Hydrozoa) in the White Sea

Populations of the colonial hydroid Obelia geniculata in the White Sea reproduce asexually by frustule formation. Young medusae appear in the plankton during July and August. The number of medusae rarely exceeds 36 per m³, and the average number varies every year from 0.4 to 10 per m³. The size of medusae is smaller than reported from other regions. The umbrella of the largest recorded medusa was only 0.57 mm in diameter and the specimen had just 35 tentacles. Only a few mature medusae were found during the study. The colonies in the White Sea are epiphytic and grow only on laminarian thalli. At the beginning of July there are no colonies on thalli from the upper subtidal zone. By the end of August, colonies of O.␣geniculata had increased in density to 30 per m². Hydroid recruitment was attributed to active frustule production by colonies living below that zone. The frustules detach from the stems of the hydroids and are found in plankton. Production of frustules on branches occurs continuously during colony growth until water temperatures climb above 0 °C. We found that water temperature in this Arctic environment is generally too low for medusa maturation and planula development in the species. Propagation by frustule formation is the principal means of reproduction in Obelia geniculata within the White Sea, and this phenomenon accounts for the species being a dominant epiphyte on laminarian thalli there.     

桃花水母生活史的实验观察

记录了中国产信阳桃花水母(Craspedacusta xinyangensis)的生活史及各阶段主要发育特征。25～28℃条件下,卵受精23h后发育成长0.14～0.21mm的圆棍状浮浪幼虫,养殖环境下,浮浪幼虫在水中漂浮3～5d后固定到人工玻璃底质上,3～4d后发育成长度0.3～0.6mm的螅状体。水螅体产生无纤毛的类浮浪幼虫形成新的螅状体。一个螅状体成熟后产生一个水母芽,新释放的幼水母具有16只触手。     

Serotonin involvement in the metamorphosis of the hydroid Eudendrium racemosum

Hydroid planulae metamorphose in response to an inducing external stimulus, usually a bacterial cue. There is evidence that neurotransmitters participate in the signal transduction pathway of hydroid metamorphosis. Eudendrium racemosum is a colonial hydroid common in the Mediterranean Sea. It lacks the medusa stage and the planulae develop on female colonies during the fertile season. In this work, serotonin (5-HT) was localized in some planula ectodermal cells. Co-localization of serotonin and beta-tubulin suggested that 5-HT was present in sensory nervous cells and in different ectodermal cells. To investigate the role of neurotransmitters in metamorphosis, E. racemosum planulae were treated with serotonin and dopamine and with agonists and antagonists of the corresponding receptors. Serotonin and a serotonin receptor agonist induced metamorphosis, while a 5-HT receptor antagonist inhibited it. Dopamine and all dopaminergic drugs used did not show any significant effect on the onset of metamorphosis. Results from this work showed that 5-HT could stimulate metamorphosis in E. racemosum planulae in the presence of a natural inducer. A mechanism by which this neurotransmitter could act in this phase is proposed.     

Experimentelle Untersuchungen zum Stockwachstum und zur Medusenbildung bei dem marinen HydrozoonEirene viridula

The development of both slide-grown and non-substrate bound colonies ofE. viridula (Thecata-Leptomedusae) ranging in size from 1 to 50 hydranths was investigated under various temperature conditions. The majority of slide-grown colonies reached a larger final size than non-substrate bound ones, in 20°, 25° and 29° C. Raising the temperature did not stimulate propagation of hydranths as expected. Most of the colonies transferred to 25° or 29° C finally were even smaller than those reared at 20° C. This was partially due to resorption of several hydranths about 9 days after the temperature rise; the influence of “physiological competition” between development of new hydranths and budding of medusae on colony growth is discussed. Transfer from higher to lower temperatures affected colony growth negatively. Raising the temperature from 20° to 25° or 29° C initiated formation of gonozooids from the distal part of hydranth stalks and development of medusa buds in both types of colonies. With the exception of slide-grown colonies transferred to 25° C, also young medusae were budded off. There was a remarkable coincidence in predominance of colony growth in slide-grown colonies and of medusa budding in non-substrate bound cultures. In the latter, medusa buds developed 1 to 2 days earlier. Most buds did not differentiate into liberated medusae, but were resorbed. Transformation of medusa buds into hydranths was not observed. In the clone ofE. viridula, onset of medusa budding did not depend on a “minimal colony size”. Even single hydranths were able to produce medusa buds after transfer to higher temperatures; budded off medusae were recorded from non-substrate bound colonies with an initial size of 3 hydranths. In slide-grown cultures, medusa buds developed into colonies with an initial size of only 3 hydranths. No hydranth propagation prior to medusa budding occurred in these cases. After raising temperature from 25° to 29° C medusa buds were observed in nonsubstrate bound colonies only; a small number of medusae were budded off from some of these colonies. Lowering the temperature from 29° or 25° to 20° C caused resorption of existing medusa buds. In several non-substrate bound colonies, transfer from 29° to 25° C induced development of gonozooids with medusa buds and, in some cases, of young medusae. Incubation with the alkylating cytostaticTrenimon and transfer from 20° to 25° C caused irreversible resorption of all hydranths when 4 × 10^?2 mg/ml were administered for 10 mins. Thereafter, only development of stolonial structures was observed. With one exception, the colonies treated with 4 × 10^?3 mg/ml, and all others submitted to 4 × 10^?4 mgTrenimon/ml were able to produce new hydranths and also medusa buds; some of the colonies first had to overcome a degressive phase. Treatment with 4 × 10^?2 mg destroyed all interstitial cells (I-cells). Incubation with 1 × 10^?3 or 1 × 10^?4 mg/ml left the I-cells at least partially intact. It is concluded that I-cells are indispensable for hydranth and medusan morphogenesis inE. viridula.     

A new hydroid from the Upper Cretaceous of Mississippi

A new fossil hydroid is reported as an organic impression on a calcareous gastropod steinkern from the Prairie Bluff Chalk (Maastrichtian), Oktibbeha County, Mississippi. This is the first such hydroid reported from the Upper Cretaceous of the Atlantic Coastal Plain. The fossil organism consists of anastomosing hydrorhizae forming a holdfast, a fascicled hydrocaulus, and elongated, crenulated and ribbed hydrothecae. The fossil is unlike other Mesozoic hydroids that have been reported from Europe and North America; it is described as Mesodendrium oktibbehaensis gen. et sp. nov. and tentiatively referred to an extant family, the Campanulariidae (Calyptoblastina). The complete preservation of the holdfast, hydrocaulus and hydrothecae suggests that this hydroid lived inside gastropod shells. In analogy with Recent symbiotic hydroids inhabiting mollusc shells, the new specimen described here possibly represents the oldest known example of a symbiotic relationship between hydroids and hermit crabs.     

Synchronized release of medusae from three species of hydrozoan fire corals

 The release of medusae from three hydrozoan fire corals, Millepora dichotoma, M. murrayi and M. platyphylla, was investigated at three sites in southern Taiwan from February 1994 to July 1995. All three species were gonochoristic, and developed and released several batches of medusae between April and May. The duration of open ampulla appearing on the surface of coralla was short, about three months, and could be used to infer the reproductive season of the fire corals between April and May. No obvious lunar cycles of medusa release were found in these species. Medusa release started before dark at approximately 17:00 h and continued for several hours. Males began releasing medusae earlier than females. Synchronization of medusa release between colonies, i.e., the probability of occurring on the same nights, was significantly higher within a species than between different species. Hybridization in nature among the three species is, therefore, unlikely due to segregation in the spawning dates. Moreover, the synchronization within each species was often significantly higher within versus between sites. The free-swimming medusae released gametes within approximately one hour, and the spent medusae lived for a few more hours. Medusae may facilitate fertilization rates as a result of an apparently negatively geotactic swimming response that results in medusa aggregation at the surface. No differences in the sizes of medusae, eggs and sperm were detected among the three species; however, some characteristic differences of medusa nematocysts were found. Accepted: 25 September 1997     

水母雪莲培养细胞对糖尿病小鼠血糖的影响

目的:探讨水母雪莲细胞培养物对糖尿病小鼠的降血糖作用。方法:将KKay糖尿病小鼠随机分为水母雪莲组、二甲双胍组和对照组,连续灌胃6周,每7 d称重并测量给药后3 h的空腹血糖,6周后测试药物的时-效关系及动物的糖耐量,最后检测甘油三酯、胆固醇、血清胰岛素等生化指标。结果:KKay小鼠饲喂雪莲7 d后,血糖值明显下降(P0.01),在此后的5周时间内,一直维持在较低血糖水平,其效应与阳性药物二甲双胍类似。连续给药6周后,雪莲组动物的糖代谢调节能力得到明显改善,甘油三酯、胆固醇、血清胰岛素较对照组显著降低。与二甲双胍组相比,雪莲的时-效关系表现为起效时间长、维持时间久等特点,即血糖值在给药后6 h明显下降,14 h达到最低,20 h左右逐渐恢复到给药前水平;而二甲双胍在给药后2 h即可见血糖明显下降,6 h血糖值最低,14 h后逐渐恢复到药前水平。结论:雪莲细胞培养物能有效降低KKay糖尿病小鼠的血糖水平,其作用机制可能与胰岛素的敏感性增加以及脂代谢调节有关。     

Effects of turbulence on the feeding rate of a pelagic predator: The planktonic hydroid Clytia gracilis

Relatively little is known about the role of turbulence in a predator-prey system where the predator is a passive, pelagic forager. The Campanulariid hydroid Clytia gracilis (Cnidaria, Hydrozoa) is unusual because it occurs as planktonic colonies and is reported to forage passively in the water column on Georges Bank, Massachusetts, USA. In this study, we investigated the role of various turbulence conditions on the feeding rate of C. gracilis colonies in laboratory experiments. We found a positive relationship between turbulence velocities and feeding rates up to a turbulent energy dissipation rate of ca. 1 cm² s^− 3. Beyond this threshold feeding rate decreased slightly, indicating a dome-shaped relationship. Additionally, a negative relationship was found between feeding efficiency and hydroid colony size under lower turbulent velocities, but this trend was not significant under higher turbulence regimes.