A jellyfish-eating sea anemone (Cnidaria,Actiniaria) from Palau: Entacmaea medusivora sp. nov.

Entacmaea medusivora sp. nov., a member of the family Actiniidae, inhabits Jellyfish Lake in Palau, western Caroline Islands, and eats the rhizostome jellyfish Mastigias papua. The anemone is azooxanthellate, despite its jellyfish prey containing symbiotic algae. Well fed anemones released ciliated planula-like larvae in the laboratory when maintained at more than 30 °C. It could not be determined whether the larvae, which usually settled around the parent within 24 h of release, were produced sexually or asexually.     

An ultrastructural study of the establishement of the testicular cysts during spermatogenesis in the sea anemone Actinia fragacea (Cnidaria: Anthozoa)

Spermatogenesis in the sea anemone Actinia fragacea takes place in numerous testicular cysts located in the mesoglea of the gonads. Prospermatogonia arise among the bases of the gonadal epithelial cells bordering the mesoglea, and later migrate into the mesoglea to establish the cysts. The prospermatogonia arise singly, but soon most are found as small groups within the endoderm. They are small cells, 6–7 μm in diameter, and have relatively large nuclei with a single nucleolus. Their cytoplasm is dense, and contains dense bodies and nuage material as well as Golgi, mitochondria, and individual cisternae of endoplasmic reticulum. Each prospermatogonium bears a flagellum, originating in a groove or channel in the cytoplasm. A small proportion of prospermatogonia enter the mesoglea singly, but most migrate as elongate groups or “slugs” of cells. As they enter, the groups often become constricted into hour-glass shapes, and they become covered by the endodermal basal lamina. During the later stages of entry, the last part of the group to enter retains contact with the bases of the epithelial cells, which are dragged into the mesoglea behind the germ cells. This contact between germ cells and endoderm persists throughout spermatogenesis and prevents closure of the mesoglea behind the group. The endodermal cells involved begin specialization to form the trophonema. Once entry is complete, the groups enlarge rapidly to form the testicular cysts. A small number of germ cells appear to remain behind in the endoderm after most have entered the mesoglea, and the possible significance of these cells is discussed.     

A new species of sea anemone (Cnidaria: Anthozoa: Actiniaria) from Manus Basin hydrothermal vents, South-western Pacific

During the BIOACCESS Japanese cruises (1996 & 1998), active hydrothermalism and associated vent fauna were studied on the South-eastern Rift of Manus Basin (South-western Pacific). In the PACMANUS vent field, a conspicuous vent fauna was sampled, including an actinostolid sea anemone (Actiniaria) belonging to an undescribed genus and species. Pacmanactis hashimotoi gen. et spec. nov. is here described, and represents the 9th sea anemone reported from hydrothermal vents.     

Distribution of sea anemones (Cnidaria,Actiniaria) in Korea analyzed by environmental clustering

Hydrobiologia - Using environmental data and the geospatial clustering tools LOICZView and DISCO, we empirically tested the postulated existence and boundaries of four biogeographic regions in the...     

Phylogenetic relationships among sea anemones (Cnidaria: Anthozoa: Actiniaria)

Sea anemones (order Actiniaria) are among the most diverse and successful members of the anthozoan subclass Hexacorallia, being found at all depths and latitudes and in all marine habitats. Members of this group exhibit the greatest variation in anatomy, biology, and life history in Hexacorallia, and lack any morphological synapomorphy. Nonetheless, previous molecular phylogenetic studies have found that Actiniaria is monophyletic with respect to other extant hexacorallians. However, relationships within Actiniaria have remained unresolved, as none of these earlier works have included sufficient taxon sampling to estimate relationships within Actiniaria. We have analyzed sequences from two mitochondrial and two nuclear markers for representatives of approximately half of the family-level diversity within the order, and present the first phylogenetic tree for Actiniaria. We concur with previous studies that have suggested that molecular evolution is unusually slow in this group. We determine that taxonomic groups based on the absence of features tend not to be recovered as monophyletic, but that at least some classical anatomical features define monophyletic groups.     

Tropomyosin isoforms present in the sea anemone,Anthopleura japonica (Anthozoa,Cnidaria)

Five isoforms of tropomyosin, designated as TMa, TMb, TMc, TMd, and TMe, were detected in the sea anemone, Anthopleura japonica. The apparent molecular weights of these isoforms were estimated to be approximately 30 kD to 37.5 kD, and their pI values were approximately 4.55 (TMa and TMb) and 4.65 (TMc, TMd, and TMe). Although sea anemone tropomyosin isoforms have the ability to bind to rabbit skeletal muscle actin, they preferably bind to actin at higher concentrations of Mg(2+) (10-20 mM) and slightly lower pH (6.2-7.2) than those used in conventional conditions. Antigenic properties of sea anemone tropomyosin seemed to be considerably specific to each isoform. Distribution of tropomyosin isoforms in the sea anemone body was somewhat portion-specific. TMa, TMb, and TMe were detected similarly in the extracts from tentacle, oral disc, column, mouth, and pedal disc. Although TMc and TMd were detected abundantly in the tentacle extract and moderately in the column and mouth extracts, these components were not contained in the pedal disc extract and detected only faintly in the oral disc extract.     

Phylogenetic signal in mitochondrial and nuclear markers in sea anemones (Cnidaria, Actiniaria)

The mitochondrial genome of basal animals is generally more slowly evolving than that of bilaterians. This difference in rate complicates the study of relationships among members of these lineages and the discovery of cryptic species or the testing of morphological species concepts within them. We explore the properties of mitochondrial and nuclear ribosomal genes in the cnidarian order Actiniaria, using both an ordinal- and familial-scale sample of taxa. Although the markers do not show significant incongruence, they differ in their phylogenetic informativeness and the kinds of relationships they resolve. Among the markers studied here, the fragments of 12S rDNA and 18S rDNA most effectively recover well-supported nodes; those of 16S rDNA and 28S rDNA are less effective. The general patterns we observed are similar to those in other hexacorallians, although Actiniaria alone show saturation of transitions for ordinal-scale analyses.     

Nematocysts of sea anemones (Actiniaria,Ceriantharia and Corallimorpharia: Cnidaria): nomenclature

A brief historical review of nematocyst terminology is given and three nomenclatural problems are discussed. It is proposed to combine the terms initiated by Weill (1934) with those of Schmidt (1969). A new mesobasic grade, intermediate between microbasic and macrobasic is proposed for amastigophores and p-mastigophores possessing a short Faltstück. A more liberal interpretation of Weill's (1934) terminology for nematocysts than that proposed by Cutress (1955) is suggested in respect of microbasic amastigophores and p-mastigophores. Basitrichs and b-mastigophores continue to be recognized as separate categories.deceased     

Different nematocytes have different synapses in the sea anemone Aiptasia pallida (Cnidaria,Anthozoa)

Sea anemones feed by discharging nematocysts into their prey, but the pathway for control of nematocyst discharge is unknown. The purpose of this study was to investigate the ultrastructural evidence of neuro-nematocyte synapses and to determine the types of synaptic vesicles present at different kinds of nematocyst-containing cells. The tip and middle of tentacles from small specimens of Aiptasia pallida were prepared for electron microscopy and serial micrographs were examined. We found clear vesicles in synapses on mastigophore-containing nematocytes and dense-cored vesicles in synapses on basitrich-containing nematocytes and on one cnidoblast with a developing nematocyst. In addition, we found reciprocal neuro-neuronal and sequential neuro-neuro-nematocyte synapses in which dense-cored vesicles were present. It was concluded that : (1) neuro-nematocyte synapses are present in sea anemones, (2) different kinds of synaptic vesicles are present at cells containing different types of nematocysts, (3) synapses are present on cnidoblasts before the developing nematocyst can be identified and these synapses may have a trophic influence on nematocyst differentiation, and (4) both reciprocal and sequential synapses are present at the nematocyte, suggesting a complex pathway for neural control of nematocyst discharge. J. Morphol. 238:53–62, 1998. © 1998 Wiley-Liss, Inc.     

The breakdown of symbiotic zooxanthellae in the sea anemone Phyllactis (=Oulactis) flosculifera (Actiniaria)

The sea anemone Phyllactis (=Oulactis) flosculifera Lesueur (Actiniaria) has developed specialized adaptations of a structural, behavioural and chemical nature, which allow the farming of its symbiotic zooxanthellae as well as their breakdown and use as a source of nutrition. The presence of an extension of the upper column, the ruff, increases the exposed surface area, and the pattern of expansion and contraction of ruff and tentacles allows the high standing crop of algal symbionts they contain maximum exposure to illumination. A protein extract from the combined ruff, oral disc and tentacles has a destructive effect in vitro on the zooxanthellae of Phyllactis (52%), Aiptasia (37·5%) and Zoanthus (16%). Intracellular degeneration of zooxanthellae is greatest in the phagocytic cells of the trefoil forming the free end of the upper mesentery, but also occurs in other parts of the mesentery. The algal pellet extruded by Phyllactis consists mostly of debris, testifying to the anemone's ability to break down its zooxanthellae. Aiptasia tagetes Duch. & Mich, shows only a simple phototactic response, has no algal-damaging agent and very few degenerate zooxanthellae in its mesenteries, but it extrudes large numbers of its symbionts in all stages of the life history.     

Internal brooding favours pre-metamorphic chimerism in a non-colonial cnidarian, the sea anemone Urticina felina

The concept of intraorganismal genetic heterogeneity resulting from allogeneic fusion (i.e. chimerism) has almost exclusively been explored in modular organisms that have the capacity to reproduce asexually, such as colonial ascidians and corals. Apart from medical conditions in mammals, the natural development of chimeras across ontogenetic stages has not been investigated in any unitary organism incapable of asexual propagation. Furthermore, chimerism was mainly studied among gregarious settlers to show that clustering of genetically similar individuals upon settlement promotes the occurrence of multi-chimeras exhibiting greater fitness. The possible occurrence of chimeric embryos and larvae prior to settlement has not received any attention. Here we document for the first time the presence of natural chimeras in brooded embryos and larvae of a unitary cnidarian, the sea anemone Urticina felina. Rates of visible bi- and multi-chimerism of up to 3.13 per cent were measured in the broods of 16 females. Apart from these sectorial chimeras, monitored fusion events also yielded homogeneous chimeric entities (mega-larvae) suggesting that the actual rates of natural chimerism in U. felina are greater than predicted by visual assessment. In support of this assumption, the broods of certain individuals comprised a dominant proportion (to 90%) of inexplicably large embryos and larvae (relative to oocyte size). Findings of fusion and chimerism in a unitary organism add a novel dimension to the framework within which the mechanisms and evolutionary significance of genetic heterogeneity in animal taxa can be explored.     

Asexual reproduction and molecular systematics of the sea anemone Anthopleura krebsi (Actiniaria: Actiniidae)

In this paper we use allozyme analyses to demonstrate that individuals in Anthopleura krebsi aggregates are monoclonal. Additionally, sympatric samples of the red and the green colour-morphs of A. krebsi from Pernambuco, Brazil were genetically compared and no significant differences were observed between them (gene identity = 0.992), indicating that they do not belong to different biological species. All individuals within aggregates of the green colour-morph were found to be identical over the five polymorphic loci analysed. Such results would be extremely unlikely (P < 10(-11)) if the individuals analysed had been generated through sexual reproduction, thus confirming the presence of asexual reproduction in this species.     

Actiniaria and Ceriantharia of the Azores (Cnidaria Anthozoa)

The common shallow water species of sea anemones (Actiniaria) and tube anemones (Ceriantharia) of the Azores are listed. Eight species of sea anemones are mentioned, the species Cereus pedunculatus and Sagartia affinis being new records for the archipelago. Both species of Ceriantharia, namely Arachnanthus nocturnus and Pachycerianthus solitarius, are recorded from the Azores for the first time. Arachnanthus nocturnus is also recorded from the Cape Verde Islands and from Madeira for the first time. Communicated by H.-D. Franke     

Growth, reproduction and survival of a tropical sea anemone (Actiniaria): benefits of hosting anemonefish

The ecological performance of the sea anemone Heteractis magnifica was examined during a 36-month experiment with respect to season and the presence and numbers of a mutualist (orange-fin anemonefish Amphiprion chrysopterus). Anemones primarily grew during the autumn, with most asexual reproduction occurring in winter; mortality was not strongly seasonal. Individual growth rates did not differ between anemones harboring one or two anemonefish, but these rates were three times faster than for anemones lacking Amphiprion. Anemones with two anemonefish had the highest fission rate, whereas those without anemonefish had the lowest. By contrast, anemones that were not defended by anemonefish suffered higher-than-expected mortality. As a consequence, anemones with two Amphiprion had the greatest net increase in surface area, and those lacking anemonefish had a negligible gain that was statistically indistinguishable from zero after three years. Anemonefish not only enhanced anemone survivorship as previously believed, they also fostered faster growth and more frequent asexual reproduction.     

Redescription and biological aspects ofHormathia alba (Andres, 1881), a luminescent sea anemone (Anthozoa,Actiniaria)

The sea anemoneHormathia alba (Andres, 1881) is redescribed and definitely established as distinct fromH. coronata. Synonymy, external morphology, anatomy and cnidom are treated in detail. Aspects of its reproduction, ecology, distribution and distinctive characteristics are also reported. The species, largely mistaken throughout literature, is rather common on Mediterranean infralittoral soft bottoms. It has also been found in the SW of Ireland. This is the only known sea anemone with luminescence, a feature that has never been reported before.     

Gametogenic cycles and reproduction in the beadlet sea anemone Actinia equina (Cnidaria: Anthozoa)

Sexual Actinia equina have been maintained in the laboratory. Monthly biopsies show that these animals have annual gametogenic cycles. Regular samples from several natural populations suggest that animals in the wild show similar gametogenic periodicity. In the laboratory, males release sperm, but females brood young, at least for a few weeks. Members of these broods are released sporadically, usually after a water change. Males and non-sexual adults kept in isolation for over a year release a few juveniles during and at the end of that time. These young are likely to be asexually reproduced. There appears to be geographical variation of anemone size and in the frequency of sexual individuals in populations round the British Coast, so that modes of reproduction may vary.     

A study of the spirocytes from the Ceriantharia and Actiniaria (Cnidaria: Anthozoa)

Summary The structure and ultrastructure of ceriantharian and actiniarian spirocysts were compared. In the ceriantharian spirocyst, the apical cap consisted of two layers and the wall consisted of three, whereas in the actiniarian spirocyst, the number of layers was reversed. The inner wall of the ceriantharian spirocyst was smooth in longitudinal section whilst that of the actiniarian was serrated. The apical ends of ceriantharian spirocytes posessed either a set of microvilli or an arrangement that included both microvilli and a flagellum. The actiniarian spirocyte possessed only microvilli. Fine tubules occupying the undischarged tube of the ceriantharian spirocysts were of both moderate and strong electron densities, whilst those of the actiniarian were consistently electrondense. Undischarged ceriantharian spirocytes possessed tubules situated in the pleats and in the centre of the tube, whilst the tubes of undischarged actiniarian spirocytes possessed only centrally placed tubules. Fine electron-dense filaments linking the cell membrane to the spirocyst were present at the apical ends of actiniarian spirocytes. A different electron-dense network of filaments was present in the apical end of ceriantharian spirocytes. All cnidae of ceriantharians lacked tripartite opercula whilst the nematocysts of actiniarians possessed them. Primitive features of ceriantharian cnidae are discussed.     

Features of biology of the sea anemone Charisea saxicola Torrey, 1902 (Actiniaria: Condylanthidae) from the northwest Pacific

The first data on features of the biology of the sea anemone Charisea saxicola, which is widespread in the Northwest Pacific, were obtained. That species, inhabiting the littoral of Shikotan Isl. (the Minor Kurile Ridge), belongs by its trophological attributes to nonselective deposit feeders. Animals swallow soil together with the organisms in it, not separating mineral particles from organic ones. Populations of Ch. saxicola are presented by individuals of mail and female sex, however the females prevailed in number. Hermaphrodites and evidence of sex change were not revealed in that species. Females were in the postspawning condition in all settlements. Spermatogenic cells of the new generation at two stages of development were recorded in males.