Convenient nomenclature of cysteine-rich polypeptide toxins from sea anemones

Polypeptide toxins are the main constituents of natural venoms. Considerable progress in the study of these molecules has resulted in the determination of a large number of structurally related sequences. To classify newly discovered molecules, a rational nomenclature for naming peptide toxins was developed, which takes into account toxin biological activity, the species name, and structural peculiarities of the polypeptide. Herein, we suggest modifications to this nomenclature for cysteine-rich polypeptide toxins from sea anemones and describe 11 novel polypeptide structures deduced after common database revision.     

A new species of Hormathia (Actiniaria, Hormathiidae) from the eastern Weddell Sea, Antarctica

A new species of sea anemone in the genus Hormathia, is described and illustrated based on forty-two specimens collected during the Polarstern cruises ANT XV/3 and ANT XVII/3 in the Weddell Sea. The main features of the new taxon are the crown of flattened and hooked tubercles at the distal end of the scapus, the regular arrangement of pointed tubercles along the column and the cnidom. The new species shares the pointed tubercles, at least in the upper part of the scapus, with two other species of Hormathia in the southern hemisphere: Hormathia spinosa Hertwig 1882 and H. pectinata Hertwig 1882 Received in revised form: 27 December 2000 Electronic Publication     

New family of sea anemones (Actiniaria,Acontiaria) from deep polar seas

We describe and illustrate two new species from polar deep seas that belong to a new genus and family. Antipodactidae fam. nov. is characterized by acontia with macrobasic p-amastigophores; this type of nematocyst has never been reported from acontia. Antipodactis gen. nov. is characterized by a column with a distinct scapus and scapulus, cuticle-bearing tenaculi on the scapus, more mesenteries proximally than distally, mesenteries regularly arranged, restricted and reniform retractor musculature, and macrobasic p-amastigophores in the acontia. Antipodactis scotiae sp. nov. and A. awii sp. nov. differ in number of mesenteries, retractor and parietobasilar muscles, cnidae, and geographic distribution. We discuss the familial and generic characters of Antipodactis gen. nov. and its relationship to other families of acontiarian sea anemones: it most closely resembles members of Kadosactidae in terms of anatomy and some aspects of cnidom, and has a cnidom identical to that of Diadumenidae in terms of the types of nematocysts. Because the morphology of nematocysts is critical to the diagnosis of this family, we review and comment on the nomenclature of mastigophores. The macrobasic p-amastigophores of Antipodactidae fam. nov. conform to England’s (Hydrobiologia 216/217:691–697, 1991) definition rather than that of Mariscal (Coelenterate Biology. Academic Press, New York, pp 129–178, 1974).     

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.     

Effects of asexual reproduction on population structure of Sagartia elegans (Anthozoa: Actiniaria)

Sagartia elegans propagates asexually by pedal laceration. The effects of this method of reproduction on local population structure were investigated. Localized clones with discrete clonal boundaries occur. Expansion of individual clones may be extensive (tens of metres), but areas of uninhabitable substrate constitute an almost complete barrier to such dispersal. Short term, local recruitment is infrequent and appears to be dominated by pedal laceration but, despite the predominance of asexual reproduction, genotypic diversity is high, few populations being dominated by individual clones.     

Predation on symbiont sea anemones by their host hermit crab Dardanus pedunculatus

Feeding by host hermit crabs Dardanus pedunculatus on their symbiotic sea anemones Calliactis polypus was investigated using animals collected at Shirahama, Wakayama Prefecture, Japan. In the first experiment, changes in the number of sea anemones on hermit crab shells were recorded in single‐and double‐crab trials without food and single‐crab trials with food. The number of sea anemones significantly decreased under starved conditions. The extent of this decrease per single hermit crab was higher in the double‐crab trials than in the single‐crab trials. Direct observations and video recordings showed that hermit crabs occasionally removed sea anemones from their own shells, and also from partners’ shells in the double‐crab trials, and consumed them. In the second experiment, fed and unfed hermit crabs with or without sea anemones were examined for body weight changes. Fed hermit crabs gained weight whereas unfed hermit crabs lost it. The degree of weight loss in unfed hermit crabs was significantly higher in those without sea anemones, which indicates some value of the latter as food. We offer some speculations on the course of development of this symbiosis, with predation on sea anemones having played an important initial role.     

Effects of long-term ultraviolet radiation: the white form of Metridium senile (Anthozoa: Actiniaria) as a potential biological indicator for ultraviolet

Genetically identical individuals of the white form of Metridium senile were kept in the laboratory for 40 months, during almost 2 years of which they were irradiated with ultraviolet (UV) radiation simulating the shape of the solar UV spectrum. The living and experimental conditions were largely matched to the conditions in the sea anemones' natural habitat on the North Sea coast. Controls were shielded from direct radiation or irradiated with only the visible range of the spectrum; for the UV tests, the UV component corresponded either to the conditions in the natural habitat or to twice or 4 times this dose. All experiments were preceded by a several-month settling-in period, and UV irradiation was always begun at a low intensity. Under these conditions UV was not lethal but produced many parameter changes, of which only those that were irreversible for the entire duration of the experiment, from September 1992 to August 1994, are described here. The body mass fell significantly in all three UV-radiation modes. All irradiated animals positioned themselves so as to be less exposed to the radiation, and all changed colour from white to brown. These responses are discussed with reference to the potential of M. senile as an indicator or monitor for UV in the northern European coastal region. Field analyses are currently being conducted to demonstrate the extent to which the present results apply to field conditions. Received in revised form: 30 May 2000 Electronic Publication     

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...     

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     

Direct attachment of eggs to the body wall in the externally brooding sea anemone <Emphasis Type="Italic">Cnidopus japonicus</Emphasis> (Actiniaria; Actiniidae)

The externally brooding sea anemone Cnidopus japonicus (Verrill) inhabits boulder shores between the mid-intertidal and shallow subtidal zones of Mutsu Bay, northern Japan. The anemones usually adhere to the side and under-surfaces of boulders. These anemones keep offspring on the middle part of their body wall during the breeding season. Our observations of spawning behavior in an aquarium revealed that this anemone lays eggs through an elongated oral margin and directly attaches the eggs to its body wall, while making a circular groove on the column. The anemone rotates its elongated oral margin around its body trunk several times and arranges eggs in the circular brooding groove. This behavior suggests that mother anemones, regardless of their attachment position on substrata, are able to attach their offspring effectively to their body wall. Electronic Publication     

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.     

Kunitz-type protease inhibitors from acrorhagi of three species of sea anemones

Sea anemones are rich in biologically active polypeptides such as toxins and protease inhibitors. These polypeptides have so far been isolated from whole bodies, tentacles or secreted mucus. Recently, two novel peptide toxins with crab lethality have been isolated from acrorhagi (specialized aggressive organs elaborated by only certain species of sea anemones belonging to the family Actiniidae) of Actinia equina. This prompted us to survey biologically active polypeptides in the acrorhagi of two species of sea anemones, Anthopleura aff. xanthogrammica and Anthopleura fuscoviridis. No potent crab lethality was displayed by the acrorhagial extracts of both species. However, significantly high protease inhibitory activity was instead detected in the acrorhagial extracts of the two species and also in that of A. equina. From the acrorhagi of A. equina, A. aff. xanthogrammica and A. fuscoviridis, one (AEAPI), one (AXAPI) and two (AFAPI-I and AFAPI-III) protease inhibitors were isolated, respectively. The complete amino acid sequences of the four inhibitors were elucidated by N-terminal sequencing and sequencing of the C-terminal peptide fragment produced upon asparaginylendopeptidase digestion. The determined amino acid sequences revealed that all the four inhibitors are new members of the Kunitz-type protease inhibitor family.     

Juvenile Thalassoma amblycephalum Bleeker (Labridae, Teleostei) dwelling among the tentacles of sea anemones: A cleanerfish with an unusual client?

At least 51 species of fishes are facultative symbionts of sea anemones. Most of the behavioural, ecological and physiological aspects of these associations including their costs and benefits are unknown. We recorded the behaviour and the habitat use of eight assemblages (three or ten specimens each) of the juvenile wrasse Thalassoma amblycephalum dwelling among the tentacles of the two sea anemones Entacmaea quadricolor (clonal type), and Heteractis magnifica at a coral reef in southern Japan during 16 months in daylight hours. There are only two past records of this facultative association, one from east Africa and one from Indonesia. The wrasse remained close to and was occasionally in physical contact with the host when foraging amongst the tentacles. When frightened, they took shelter among corals, away from the host anemone. The wrasse co-existed with the anemonefishes Amphiprion frenatus in E. quadricolor and A. ocellaris in H. magnifica. By using forced host contact tests ex situ and scanning electron microscopy examination of the fish epidermis, we show that juveniles of this wrasse are protected from E. quadricolor, but possibly not from H. magnifica. We suggest that juvenile T. amblycephalum dwelling among the tentacles of sea anemones are cleanerfish with an unusual client, in that they appear to clean mucus and, or, necrotic tissue from the sea anemone host.     

Toward a natural classification: phylogeny of acontiate sea anemones (Cnidaria,Anthozoa, Actiniaria)

Acontia—nematocyst‐dense, thread‐like extensions of the mesenterial filaments―are the characteristic feature of the actiniarian group Acontiaria. Phylogenetic analyses have shown that acontiate taxa form a clade that also includes some taxa without acontia. We analyse five molecular markers from 85 actiniarians to explore the phylogenetic relationships among families in Acontiaria, including acontiate species assigned to other higher taxa and species without acontia that have been allied to Acontiaria. Based on our results, we redefine the group to accommodate those lineages that have lost acontia, and formalize it as superfamily Metridioidea. Based on stable and well supported clades, we resurrect Phelliidae and Amphianthidae, redefine Kadosactinidae and Actinoscyphiidae, and move two species to new genera: that previously termed Sagartiogeton erythraios belongs in Jasonactis gen. nov.; and that previously termed Anthosactis pearseae belongs in Ostiactis gen. nov., type genus of Ostiactinidae fam. nov. We also synonymized Halcampoididae and Halcampidae (as Halcampidae) and Andvakiidae and Isophelliidae (as Andvakiidae). The results of our phylogenetic analyses indicate that the diagnostic morphological characters used in the family‐level taxonomy of acontiate actiniarians such as the nematocysts of the acontia, the marginal sphincter muscle, and mesenteries divisible into macro‐ and micro‐cnemes, have to be revisited, as these features are highly homoplasious.     

About lipids and toxins

Many mono or multicellular organisms secrete soluble proteins, referred to as protein toxins, which alter the behavior of foreign, or target cells, possibly leading to their death. These toxins affect either the cell membrane by forming pores or modifying lipids, or some intracellular target. To reach this target, they must cross one of the cellular membranes, generally that of an intracellular organelle. As described in this minireview, lipids play crucial roles in the intoxication process of most if not all toxins, by allowing/promoting binding, endocytosis, trafficking and/or translocation into the cytoplasm.     

Novel proteinaceous toxins from the nematocyst venom of the Okinawan sea anemone Phyllodiscus semoni Kwietniewski

The Okinawan sea anemone Phyllodiscus semoni is known to cause cases of severe stinging. We isolated P. semoni toxins 60A and 60B (PsTX-60A and PsTX-60B; ca. 60 kDa) as the major toxins from the isolated nematocysts of this species for the first time. PsTX-60A and PsTX-60B showed lethal toxicity to the shrimp Palaemon paucidence when administered via intraperitoneal injection (LD(50) values: 800-900 and 800 microg/kg, respectively) and hemolytic activity toward a 0.8% suspension of sheep red blood cells (ED(50) values: 600 and 300 ng/ml, respectively). Furthermore, we sequenced the cDNA encoding PsTX-60A. The deduced amino acid sequence of PsTX-60A did not show any similarity to previously reported proteins. The N-terminal amino acid sequence of PsTX-60B showed homology with that of PsTX-60A. These toxins represent a novel class of cytolytic proteinaceous toxins.     

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.     

Neurotoxin localization to ectodermal gland cells uncovers an alternative mechanism of venom delivery in sea anemones

Jellyfish, hydras, corals and sea anemones (phylum Cnidaria) are known for their venomous stinging cells, nematocytes, used for prey and defence. Here we show, however, that the potent Type I neurotoxin of the sea anemone Nematostella vectensis, Nv1, is confined to ectodermal gland cells rather than nematocytes. We demonstrate massive Nv1 secretion upon encounter with a crustacean prey. Concomitant discharge of nematocysts probably pierces the prey, expediting toxin penetration. Toxin efficiency in sea water is further demonstrated by the rapid paralysis of fish or crustacean larvae upon application of recombinant Nv1 into their medium. Analysis of other anemone species reveals that in Anthopleura elegantissima, Type I neurotoxins also appear in gland cells, whereas in the common species Anemonia viridis, Type I toxins are localized to both nematocytes and ectodermal gland cells. The nematocyte-based and gland cell-based envenomation mechanisms may reflect substantial differences in the ecology and feeding habits of sea anemone species. Overall, the immunolocalization of neurotoxins to gland cells changes the common view in the literature that sea anemone neurotoxins are produced and delivered only by stinging nematocytes, and raises the possibility that this toxin-secretion mechanism is an ancestral evolutionary state of the venom delivery machinery in sea anemones.     

Stimulation of neutrophil leukocyte chemotaxis by a cloned cytolytic enterotoxin of Aeromonas hydrophila

A cytolytic enterotoxin produced by Aeromonas hydrophila, isolate SSU, has been cloned in our laboratory. This enterotoxin lysed rabbit red blood cells, destroyed Chinese hamster ovary cells, caused fluid secretion in rat ligated ileal loops, inhibited the phagocytic function of mouse phagocytes, and was lethal to mice when injected intravenously. In this study, the effect of this cytolytic enterotoxin on the chemotaxis of human leukocytes (cell line RPMI 1788) was examined. This toxin, at concentrations from 92.5 to 370 ng/ml, significantly stimulated the chemotactic activity of human leukocytes in a dose-dependent fashion. The stimulation of leukocyte chemotaxis elicited by cytolytic enterotoxin was abolished when the toxin was neutralized, heated, or exposed to low pH values. This stimulatory effect also was inhibited by various concentrations of pertussis toxin. These results demonstrated that cytolytic enterotoxin may stimulate increased chemotaxis of human leukocytes, and suggest that human leukocytes may possess cytolytic enterotoxin receptors which may be coupled to pertussis toxin-sensitive G-protein.     

Brooding sea anemones (Cnidaria: Anthozoa: Actiniaria): paragons of diversity in mode,morphology, and maternity

Brooding has been reported in at least 57 species of sea anemone. More than three quarters (44/57) of the species that are known to brood have been described since the last comprehensive treatment of brooding in this lineage. Different authors focusing on different taxonomic groups within sea anemones over the last 115 years have collectively produced an imprecise and inconsistent set of terminology with respect to brooding in general and to the variety of conditions of brooding in particular. In this review, I characterize brooding as a behavior in which offspring are retained by the adult to at least the juvenile stage, in contrast with the more common release of eggs, embryos, or larvae. Brooding occurs in two primary modes, internal and external, in which offspring may be produced via sexual or asexual means. I categorize structures associated with external brooding in three types: pits, chambers, and grooves. Early inferences that external brooding has a primarily bipolar distribution continue to be supported with current data, but it is doubtful that small size and simultaneous hermaphroditism are correlated with brooding in sea anemones. Finally, I identify open questions about brooding in sea anemones and suggest future lines of research that will broaden our understanding of this phenomenon.