Cnidae in the sea anemone Sagartiogeton viduatus (Muller, 1776) (Cnidaria,Anthozoa); A comparison to cnidae in the sea anemone Metridium senile (Linnaeus, 1761) (Cnidaria,Anthozoa)

The cnidom of the sea anemone Sagartiogeton viduatus (Muller, 1776) is described from interference‐contrast light micrographs (LMs) and scanning electron micrographs (SEMs). Special attention is given to nematocyst maturation, including the differentiation of the shaft into proximal and main regions as helical folding of the shaft wall proceeds. Comparisons are made with Metridium senile (Linnaeus, 1761), whose cnidom, with a few exceptions, is closely similar to that of S. viduatus. The two anemones possess b‐ and p‐mastigophores, p‐amastigophores, isorhizas and spirocysts. Although the majority of cnidae in S. viduatus is smaller than corresponding ones in M. senile, they are grouped into the same size classes as those of M. senile, namely small, medium and large. The main differences from M. senile cnidae are the followings: (1) Large acontia p‐amastigophores are the largest nematocysts in S. viduatus. (2) They are noticeably larger than the large acontia b‐mastigophores, and (3) they are separated from the p‐amastigophores of M. senile by the sinusoid pattern of their U‐shaped capsular matrix. (4) The large acontia b‐mastigophores are microbasic and not mesobasic as in M. Senile, and (5) they do not produce darts. (6) Another difference from M. senile is the absence of catch‐tentacle isorhizas.     

Nematocyst composition of the cubomedusan Chiropsalmus quadrigatuschanges with growth

The nematocysts of Chiropsalmus quadrigatus (Cubozoa; Cubomedusa; Chirodropidae) were examined to determine if their composition changes with an increase in body size. Fixed tentacles of specimens collected in Okinawa, Japan, were homogenized and their nematocysts were observed under a differential interference contrast microscope. Six nematocyst types were observed in medusae of all sizes microbasic mastigophores (MM), large and small trirhopaloids (lTR and sTR), holotrichous isorhizas (HI), ellipsoidal isorhizas (eI), and ovoid isorhizas (oI). Two other nematocysts, large ovoid isorhizas (loI) and microbasic euryteles (ME), were observed only in small individuals. There was also marked difference in proportion of tentacular nematocysts between small and large individuals. HI was the dominant type in small specimens, while MM and eI were predominant in large specimens. Nematocyst composition in the bell and pedalia also differed between small and large individuals. Bells of small medusae contained oI and sTR, while only oI were observed in most large individuals. The pedalia of small medusae had clusters of MM, ME, sTR, and oI. Such single clusters on pedalium bases were characteristic of small individuals. The pedalia of large individuals contained scattered oI. Tentacles of medusae are used for prey capture, so the changes in the major type of nematocysts in tentacles may reflect changes in prey type.     

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).     

Variability of cnidae within a small clonal sea anemone (Isactinia sp.)

The cnidom and intraspecific variability of cnidae within the small sea anemone Isactinia sp. were verified. The specific cnidae within the cnidom of four discrete morphological structures (tentacle, actinopharynx, mesenterial filaments, and body column) within Isactinia sp. was investigated. Microbasic b-mastigophores, microbasic p-mastigophores, basitrichs, microbasic p-amastigophores, and spirocysts were found in this species. In addition, two morphologically distinct basitrich forms, distinguishable only in a discharged state, were also found, of which basitrichs with the distinctly shorter thread were found predominately only on the body column. The distribution and abundance of cnidae types differed significantly around the body in the sea anemones, as did the length of basitrichs and spirocysts among tissue types. Cnidae length also differed significantly among individuals. Correlations between cnidae length and sea anemone size were variable, whereby cnidae size was significantly negatively correlated to sea anemone size in seven cnidae–tissue combinations, positively correlated in one, and not correlated in two. Linear regression revealed that sea anemone size was able to explain 33%–68% of variation in size of b-mastigophores, p-amastigophores, and small basitrichs from within the mesenterial filaments. Correlations were negligible or not significant in remaining cnidae–tissue combinations, however. While providing key taxonomic cnidae information, this study also highlights the variability of cnidae that may occur within a species of Isactinia.     

A comparative analysis of nematocysts in Pelagia noctiluca and Rhizostoma pulmo from the North Adriatic Sea

Nematocysts of the scyphozoans Pelagia noctiluca and Rhizostoma pulmo were examined. In R. pulmo 4 types of nematocyst were observed: heterotrichous microbasic euryteles; holotrichous isorhizas; atrichous a-isorhizas; and atrichous -isorhizas. In P. noctiluca 5 types of nematocyst were seen: heterotrichous microbasic euryteles; heterotrichous isorhizas (previously described as atrichous isorhizas); holotrichous O-isorhizas; atrichous a-isorhizas; and an undescribed type, which in its structure and discharge mechanism resembles microbasic p-mastigophores. The results show, in both P. noctiluca and R. pulmo, a greater variety of nematocysts than described in previous studies.     

Photosynthetic activity and proteomic analysis highlights the utilization of atmospheric CO2 by Ulva prolifera (Chlorophyta) for rapid growth

Free‐floating Ulva prolifera is one of the causative species of green tides. When green tides occur, massive mats of floating U. prolifera thalli accumulate rapidly in surface waters with daily growth rates as high as 56%. The upper thalli of the mats experience environmental changes such as the change in carbon source, high salinity, and desiccation. In this study, the photosynthetic performances of PSI and PSII in U. prolifera thalli exposed to different atmospheric carbon dioxide (CO₂) levels were measured. Changes in photosynthesis within salinity treatments and dehydration under different CO₂ concentrations were also analyzed. The results showed that PSII activity was enhanced as CO₂ increased, suggesting that CO₂ assimilation was enhanced and U. prolifera thalli can utilize CO₂ in the atmosphere directly, even when under moderate stress. In addition, changes in the proteome of U. prolifera in response to salt stress were investigated. Stress‐tolerance proteins appeared to have an important role in the response to salinity stress, whereas the abundance of proteins related to metabolism showed no significant change under low salinity treatments. These findings may be one of the main reasons for the extremely high growth rate of free‐floating U. prolifera when green tides occur.     

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.     

A new genus and species of isanthid sea anemone (Cnidaria: Anthozoa: Actiniaria) from Chilean Patagonia,Anthoparactis fossii n. gen. et sp

We describe a new genus and species of sea anemone from Chilean Patagonia. Anthoparactis fossii n. gen. et sp. adds another acontiate genus and species to the family Isanthidae Carlgren, 1938. Anthoparactis n. gen. differs from the other isanthid genera in having the same number of mesenteries distally and proximally, acontia with basitrichs only, and a column with verrucae distally. Anthoparactis fossii n. sp. differs from the most similar species, Isoparactis fionae Lauretta et al., 2013, in the number of cycles of mesenteries and tentacles, structures of the column, colour pattern of the oral disc, cnidae, and geographical distribution. Isanthidae now includes seven genera and 11 species.     

Arrangement of accessory cells and nematocytes bearing mastigophores in the tentacles of the cubozoan Chironex fleckeri

Nematocytes containing microbasic mastigophores are intimately associated with accessory cells in the epidermis of Chironex fleckeri. Large microbasic mastigophores may be surrounded by seven to nine such cells. Each accessory cell possesses an apical portion containing secretory droplets and a basal portion which carries a radially oriented fibre linking the cell to the underlying mesogloea. The fibre is capable of projecting and retracting the accessory cell. Junctional complexes occur between accessory cells and the apical regions of neighbouring mastigophores. Each nematocyte bearing a mastigophore contains a triggering apparatus consisting of a cnidocil surrounded by microvilli. This apparatus protrudes from an invagination in the apical region of the nematocyte and is exposed when the mastigophore is in the fire-ready position. A basket of filaments which make contact with microvilli surrounds the apical end of the nematocyst like a collar. The basket is linked via fibrous bundles which envelop the mastigophore to radially oriented fibres basally. These fibres are capable of projecting and retracting the mastigophore and its associated triggering apparatus. Up to nine such fibres were observed to be associated with a single large microbasic mastigophore. Microtubules averaging 25 nm in diameter and linked via cross bridges to electrondense material were detected in the radial fibres of both nematocytes and accessory cells. Retraction of the accessory cells and projection of nematocytes result in mastigophores being brought to the firing line and in the exposure of the cnidocil apparatus.     

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.     

Size‐structured vulnerability of the colonial cyanobacterium,Microcystis aeruginosa,to grazing by zebra mussels (Dreissena polymorpha)

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Epidermal structure of the scleractinian coral Mycetophyllia ferox: light-induced vesicles,copious mucocytes,and sporadic tentacles

Three colony fragments of the scleractinian coral Mycetophyllia ferox Wells from Florida were observed in flow-through seawater aquaria under light and dark conditions. The colonies were then anesthetized and fixed for microscopic examination. Small vesicles formed across the epidermis in response to light as gastrodermis containing approximately 1.9 × 10⁶ zooxanthellae cm⁻² migrated into them. The vesicles flattened in the dark and the gastrodermis retreated to a clumped position. The epidermis is dominated by mucus cells with more than 6300 per mm². In contrast, there are very few epidermal cnidae. The polyps lack tentacles entirely, though small tentacles do occur, albeit sporadically, along the colline walls. Colline tentacles are expanded both day and night, and there is considerable intracolonial variability in the number of cnidae within them, ranging from as few as 316 to more than 3200 per mm² tentacle. There may be several small cnidocyst batteries containing both spirocysts and nematocysts (all microbasic p-mastigophores), but the principal battery is at the tentacle tip where cnidae are much more densely packed. There is considerable variation in the ratio of the two cnidae among tentacles in the same colony. Since the tentacles occur inconsistently and do not appear to expand, their functional role is unclear. Comparisons of epidermal characters are made with other members of the genus Mycetophyllia.     

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.     

Study of cnidom and cnidogenesis in Apolemia uvaria (Lesueur, 1811) (Siphonophora physonecta)

The development of different types of cnidocystes in Apolemia uvaria (Siphonophore physonecte) has been observed in vivo, using a phase contrast microscope. The main steps of the morphological differentiation of birhopaloïdes, stenoteles, mastigophores and isorhizes are described. In all cases, the Golgi apparatus secretes a capsule and a long external tube at the anterior apex of this capsule. When the tube has reached a certain length, it invaginates in the capsule and becomes the definitive nematocystic filament. In all types of cnidocysts, the external tube, before its invagination, has the same shape as the invaginate tube. The constitution of cnidome of Apolemia uvaria, not well known up till now, is defined.     

Comparative ultrastructure of catch tentacles and feeding tentacles in the sea anemone Haliplanella

TEM observations of catch tentacles revealed that the tentacle tip epidermis is filled with two size classes of mature holotrich nematocysts and a gland cell filled with electron-dense vesicles. Vesicle production is restricted to upper-middle and tentacle tip regions, whereas holotrich development occurs in the lower-middle and tentacle base regions. Thus, catch tentacles have a maturity gradient along their length, with mature tissues concentrated at the tentacle tip. Occasional feeding tentacle cnidae (microbasic p-mastigophores and basitrichs) and mucus gland cells occur in proximal portions of catch tentacles, but are phagocytized by amoeboid granulocytes and transported to the gastrodermis for further degradation. No feeding tentacle cnidae or mucus cells occur distally in catch tentacles. Unlike catch tentacles, feeding tentacles are homogeneous in structure along their length with enidocytes containing mature spirocysts, microbasic p-mastigophore or basitrich nematocysts distributed along the epithelial surface. Cnidoblasts are recessed beneath cnidocytes, occurring along the nerve plexus. Mucus gland cells and gland cells filled with electron-dense vesicles are present in feeding tentacles, distributed at the epithelial surface. Granular phagocytes are rare in the feeding tentacle tip, but common in the tentacle base.     

Synergistic effects of HSE and LTR elements from hsp70 gene promoter of Ulva prolifera (Ulvophyceae,Chlorophyta) upon temperature induction1

Besides heat stress, the 70 kDa heat shock proteins (HSP70s) have been shown to respond to cold stress. However, the involved cis‐acting elements remain unknown. The hsp70 gene from the green macroalga Ulva prolifera (Uphsp70) has been cloned, from which one heat shock element HSE and one low‐temperature‐responsive element LTR were found in the promoter. Using the established transient expression system and quantitative GUS assay, a series of element deletion experiments were performed to determine the functions of HSE and LTR in response to temperature stress. The results showed that under cold stress, both HSE and LTR were indispensable, since deletion leads to complete loss of promoter activity. Under heat stress, although the HSE could respond independently, coexistence with LTR was essential for high induced activity of the Uphsp70 promoter. Therefore, synergistic effects exist between HSE and LTR elements in response to temperature stress in Ulva, and extensive bioinformatics analysis showed that the mechanism is widespread in algae and plants, since LTR coexists widely with HSE in the promoter region of hsp70. Our findings provide important supplements to the knowledge of algal and plant HSP70s response to temperature stress. We speculated that for algal domestication and artificial breeding, HSE and LTR elements might serve as potential molecular targets to temperature acclimation.     

Reciprocal transplantation of the heterotrophic coral Tubastraea coccinea (Scleractinia: Dendrophylliidae) between distinct habitats did not alter its venom toxin composition

Tubastraea coccinea is an azooxanthellate coral species recorded in the Indian and Atlantic oceans and is presently widespread in the southwestern Atlantic with an alien status for Brazil. T. coccinea outcompete other native coral species by using a varied repertoire of biological traits. For example, T. coccinea has evolved potent venom capable of immobilizing and digesting zooplankton prey. Diversification and modification of venom toxins can provide potential adaptive benefits to individual fitness, yet acquired alteration of venom composition in cnidarians is poorly understood as the adaptive flexibility affecting toxin composition in these ancient lineages has been largely ignored. We used quantitative high‐throughput proteomics to detect changes in toxin expression in clonal fragments of specimens collected and interchanged from two environmentally distinct and geographically separate study sites. Unexpectedly, despite global changes in protein expression, there were no changes in the composition and abundance of toxins from coral fragments recovered from either site, and following clonal transplantation between sites. There were also no apparent changes to the cnidome (cnidae) and gross skeletal or soft tissue morphologies of the specimens. These results suggest that the conserved toxin complexity of T. coccinea co‐evolved with innovation of the venom delivery system, and its morphological development and phenotypic expression are not modulated by habitat pressures over short periods of time. The adaptive response of the venom trait to specific predatory regimes, however, necessitates further consideration.     

High salt stress in the upper part of floating mats of Ulva prolifera,a species that causes green tides,enhances non‐photochemical quenching

Salt stress is a major abiotic stress factor that can induce many adverse effects on photosynthetic organisms. Plants and algae have developed several mechanisms that help them respond to adverse environments. Non‐photochemical quenching (NPQ) is one of these mechanisms. The thalli of algae in the intertidal zone that are attached to rocks can be subjected to salt stress for a short period of time due to the rise and fall of the tide. Ulva prolifera causes green tides and can form floating mats when green tides occur and the upper part of the thalli is subjected to high salt stress for a long period of time. In this study, we compared the Ulva prolifera photosynthetic activities and NPQ kinetics when it is subjected to different salinities over various periods of time. Thalli exposed to a salinity of 90 for 4 d showed enhanced NPQ, and photosynthetic activities decreased from 60 min after exposure up to 4 d. This indicated that the induction of NPQ in Ulva prolifera under salt stress was closely related to the stressing extent and stressing time. The enhanced NPQ in the treated samples exposed for 4 d may explain why the upper layer of the floating mats formed by Ulva prolifera thalli were able to survive in the harsh environment. Further inhibitor experiments demonstrated that the enhanced NPQ was xanthophyll cycle and transthylakoid proton gradient‐dependent. However, photosystem II subunit S and light‐harvesting complex stress‐related protein didn't over accumulate and may not be responsible for the enhanced NPQ.