Exumbrellar Surface of Jellyfish: A Comparative Fine Structure Study with Remarks on Surface Reflectance.

The exumbrellar surfaces of six pelagic cnidarians from three classes were ultra-structurally compared to reveal their structural diversity in relation to their gelatinous, transparent bodies. We examined two hydrozoans (Diphyes chamissonis and Colobonema sericeum), a cubozoan (Chironex yamaguchii), and three scyphozoans (Atolla vanhöffeni, Aurelia coerulea, and Mastigias papua). The exumbrellar surfaces of the mesoglea in D. chamissonis, Ch. yamaguchii, Au. coerulea, and M. papua were covered with a simple epidermis; the shapes of the epidermal cells were remarkably different among the species. The epidermal cells of Ch. yamaguchii and M. papua possessed an array of microvilli on the apical side. The array possibly reduced light reflectance and provided some other surface properties, as seen for the cuticular nipple array in tunicates, considering the length, width, and pitch of the microvilli. The reduction of light reflectance on the array of microvilli was supported by the simulation with rigorous coupled wave analysis (RCWA). Microvilli were sparse and did not form an array in metephyrae of Au. coerulea. The mesoglea matrix beneath the basal side of the epidermis was loose in all of the species. The exumbrellar side of the mesoglea was exposed only in the mesopelagic species, At. vanhöffeni and Co. sericeum, and electron-dense layer(s) covered the surface of the mesoglea. It is uncertain whether the exumbrellar epidermis is absent in these species or the epidermal cells are completely exfoliated during the sampling and handling processes. In the latter case, the electron-dense layer(s) on the mesoglea surface might originally underlie the epidermis.

SEM study of species of Oswaldella Stechow, 1919 (Cnidaria, Hydrozoa, Kirchenpaueriidae), with an annotated checklist of the species of the genus.

Oswaldella is the most speciose genus, and one of the most characteristic, of hydrozoans inhabiting the Antarctic benthic marine ecosystem. Its species have relatively many important taxonomic characters allowing for their identification. Some of them, however, are difficult to study properly with a compound microscope. With the aim of improving scientific knowledge concerning species of the genus, a SEM survey of species of Oswaldella was carried out to study key morphological characters. Fourteen out of the 27 known nominal species were considered. The study has revealed unknown important characters, such as the presence of nematothecae associated with the nematophores at the cauline apophyses, and has provided a better understanding of others, such as the shape of the nematotheca associated with the medial infrathecal nematophore. A final general discussion on some of the characters studied and on the bathymetrical and geographical distribution of all known species is also included. Finally, an annotated checklist including all known nominal species has also been assembled.

A comparative study of populations of Ectopleura crocea and Ectopleura ralphi (Hydrozoa, Tubulariidae) from the Southwestern Atlantic Ocean.

Ectopleura crocea (L. Agassiz, 1862) and Ectopleura ralphi (Bale, 1884) are two of the nominal tubulariid species recorded for the Southwestern Atlantic Ocean (SWAO), presumably with wide but disjunct geographical ranges and similar morphologies. Our goal is to bring together data from morphology, histology, morphometry, cnidome, and molecules (COI and ITS1+5.8S) to assess the taxonomic identity of two populations of these nominal species in the SWAO. We have observed no significant difference or distributional patterns between the so-called Brazilian E. ralphi and Argentine E. crocea for both morphological and molecular data. Therefore, SWAO populations of Ectopleura belong to the same species. In a broader view, it is difficult to find decisive character distinguishing E. crocea from E. ralphi, and both species have indeed recently been synonymized, with the binomen E. crocea having nomenclatural priority. Geographically broader genetic analysis should be carried out in order to test the validity of this synonymy because taxonomical procedures such as studying type specimens and documenting broad phenotypic variability have not yet been conducted.

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.

Causes and consequences of stolon regression in a colonial hydroid.

A cnidarian colony can be idealized as a group of feeding polyps connected by tube-like stolons. Morphological variation ranges from runner-like forms with sparse polyp and stolon development to sheet-like forms with dense polyp and stolon development. These forms have typically been considered in a foraging context, consistent with a focus on rates of polyp development relative to stolon elongation. At the same time, rates of stolon regression can affect this morphological variation; several aspects of regression were investigated in this context. More sheet-like forms were produced by periodic peroxide treatment, which induced high rates of stolon regression. Caspase inhibitors altered the effects of regression induced by peroxide or vitamin C. These inhibitors generally diminished physical regression and the abundance of associated reactive oxygen species. Caspase inhibitors also altered cellular ultrastructure, resulting in features suggestive of necrosis rather than apoptosis. At the same time, caspase inhibitors had little effect on reactive nitrogen species that are also associated with regression. Although regression is most easily triggered by pharmacological perturbations related to reactive oxygen species (e.g. peroxide or vitamin C), a variety of environmental effects, particularly restricted environments and an interaction between feeding and temperature, can also induce regression. Stolon regression may thus be a factor contributing to natural variation between runners and sheets.

Seasonal occurrence of Opechona pyriforme metacercariae (Digenea: Lepocreadiidae) in Eirene tenuis medusae (Hydrozoa: Leptothecata) from a hypersaline lagoon in western Gulf of Mexico.

Seasonal occurrence of Opechona pyriforme metacercariae in the Eirene tenuis population from Laguna Madre, Mexico was analyzed in zooplankton samples collected in October 1997 and January, May, and July 1998. Eirene tenuis medusae were present in May, July, and October, although parasites were found only in October and July samples. Host population density was positively correlated with both surface water temperature and salinity. Total sample prevalence was 3.74%, mean abundance of the parasite was 0.06, and intensity of infection ranged between 1 and 59 metacercariae/host. Prevalence differed significantly among seasons, while intensity of infection did not. Parasite distribution was found to be highly aggregated. Although O. pyriforme infected hydromedusae of all sizes, prevalence was higher in sizes above 2.11 mm umbrella diameter. Additionally, a tendency towards increasing intensity of infection values with increasing umbrella diameter of medusae was observed. This is the first record of E. tenuis as a second intermediate host of O. pyriforme, as well as the first record of this helminth in the Gulf of Mexico.

[Morphogenesis in colonial hydroids: pulsating rudiment splitting].

Two spatially separated processes underlie the growth and morphogenesis in hydroids (Cnidaria, Hydroidomedusa): (1) growth pulsations of the terminal growing tips and (2) cell proliferation and migration in more proximal parts of the colony soft tissues. Growing tips are morphogenetic elements of the colony that provide for the colony elongation and morphogenesis. In thecate hydroids (subclass Leptomedusae) with highly integrated colonies and monopodial shoot growth, the initiation of the lateral branches and hydranth rudiments looks like a periodic splitting of the growing tip into two or more rudiments. Published descriptions and proposed models of this process assume that the splitting results from the formation of the furrows running into the tip from its apical surface. In this study on a Sertulariidae species, we demonstrate that the visible process of the tip splitting into several rudiments begins in its proximal part. At the same time, the inner ridges are initiated at the skeleton lateral surfaces surrounding the growing tip. These ridges develop and grow along the proximodistal axis. Eventually, the opposite ridges fuse, which splits the tip into several rudiments. We propose that the tip splitting into several rudiments is impossible without the spatial regulation of the outer skeleton formation. This process explains many species-specific properties of the shoot spatial organization in thecate hydroids such as the partial or complete fusion of the zooid skeleton with the shoot stem skeleton, deflection of the distal parts of the zooid skeleton from the shoot stem axis, etc. The revealed mechanisms considerably supplements and corrects the models describing morphogenesis in colonial hydroids.

Interconnected network of ganglion-like neural cell spheres formed on hydrozoan skeleton.

Identifying scaffolds supporting in vitro reconstruction of active neuronal tissues in their 3-dimensional (3D) conformation is a major challenge in tissue engineering. We have previously shown that aragonite coral exoskeletons support the development of neuronal tissue from hippocampal neurons and astrocytes. Here we show for the first time that the porous aragonite skeleton obtained from bio-fabricated hydrozoan Millepora dichotoma supports the spontaneous organization of dissociated hippocampal cells into highly interconnected 3D ganglion-like tissue formations. The ganglion-like cell spheres expanded hundreds of microns across and included hundreds to thousands of astrocytes and mature neurons, most of them having only cell-cell and no cell-surface interactions. The spheres were linked to the surface directly or through a neck of cells and were interconnected through thick bundles of dendrites, varicosity-bearing axons, and astrocytic processes. Thus, M. dichotoma exoskeleton is a novel scaffold with the unprecedented ability to support a highly ordered organization of neuronal tissue. This unexpected organization opens new opportunities for neuronal tissue regeneration, because the spheres resemble in vivo nervous tissue having high volume of cells associated primarily through cell-cell rather than cell-matrix interactions.

Changes in the patterning of a hydroid colony.

It is a widely held view that colonial hydroids (Cnidaria, Hydroidomedusae) are formed on the basis of a repetition of uniform elements. The dominant opinion is that the equal spatial organisation of the colony exists during all stages of its development except the primary polyp, which develops from the settled larva. However, the complex structure and large dimensions of shoots in certain thecate species (subcl. Leptomedusae) suggest that the organisation of the primary shoot differs strongly from that of established colonies. The present study based on a thorough collection and examination of the collected material allowed to describe the entire sequence of the colony ontogeny in Hydrallmania falcata (Sertulariidae). The established shoots of this species are characterised by relatively large size, spiral arrangement of pinnate branches over the shoot stem, and hydranths arranged in one row along the upper side of branches. We showed that the primary shoot developing from the larva has much smaller dimensions and an alternate arrangement of hydranths. During further colony development the shoot organisation undergoes a gradual transformation ending with the emergence of large shoots with 'characteristic' species-specific features. The discovered sequence of changes in shoot patterning shows certain correlations with alterations of the growing tip dimensions. The dimensions of the growing tip seem to determine the patterning in accordance with the particular spatial location of the tip. This finding implies the necessity of a detailed reinvestigation of the entire colony development in thecate hydroids, which would make a significant contribution to the understanding of the morphogenetic evolution and patterning mechanisms within this group of colonial organisms.

Ultrastructure of the calcium-sequestering gastrodermal cell in the hydroid Hydractinia symbiolongicarpus (Cnidaria, Hydrozoa).

Large, free-floating crystals of calcium carbonate occur in vacuoles of gastrodermal cells of the hydroid Hydractinia symbiolongicarpus. Here, morphological details about the process by which these cells accumulate and sequester calcium are provided by a cytochemical method designed to demonstrate calcium at the ultrastructural level. Electron-dense material presumably indicative of the presence of calcium was EGTA-sensitive and was shown by parallel electron energy loss spectroscopy (EELS) and energy spectroscopic imaging (ESI) to contain calcium. Calcium occurred in only one cell type, the endodermally derived gastrodermal cell. In these cells, the electron-dense material appeared first as a fine precipitate in the cytosol and nucleus and later as larger deposits and aggregates in the vacuole. During the life cycle, gastrodermal cells of the uninduced planula and the planula during metamorphic induction sequestered calcium. In primary polyps and polyps from established colonies, gastrodermal cells sequestered calcium, but the endodermal secretory cells did not. Our observations support the hypothesis that gastrodermal cells function as a physiological sink for calcium that enters the organism in conjunction with calcium-requiring processes such as motility, secretion, and metamorphosis.

[Shape conservatism and shaping variability. The comparative analysis of Hydrozoa and Scyphozoa early development]. / Konservativnost' formy--variabel'nost' morfogeneza. Sravnitel'nyi analiz rannego razvitiia Hydrozoa i Scyphozoa.

The morphogenetic pathways based on the self-organization take an important part in the early development of White Sea Cnidarians--Dynamena pumila (Hydrozoa) and Aurelia aurita (Scyphozoa). Comparative analysis of their early development revealed two patterns of embryonic spatial structure reproduced in the morphogenesis of both species in spite of the differences of morphogenetic paths. These are toroidal and bilaterally symmetrical shapes. It is possible that these shapes correspond to the equilibrium states of developing system and their stable reproduction is a result of epigenetic rather than genetic program.

Differential toxicity of Physalia physalis (Portuguese man-o'war) nematocysts separated by flow cytometry.

Flow cytometric separation of Physalia physalis nematocysts resulted in isolation of the two previously reported sizes of organelles measuring 10.6 and 23.5 nm in diameter. The venom of the smaller nematocysts, which are present in greater abundance, was lethal in vitro to chick embryonic cardiocytes at doses of 0.6 microgram protein/culture, whereas 20 micrograms protein prepared from the larger nematocysts was inocuous. SDS gel electrophoresis revealed common proteins of 69,000, 82,000 and 50,000-65,000 mol. wt in the nematocyst contents of both sizes of organelles.

Cellular basis for tentacle adherence in the Portuguese man-of-war (Physalia physalis).

The fishing tentacles of Physalia physalis (Portuguese man-of-war) adhere to prey and human victims by the penetration of a barbed tubule connected to an intracellular nematocyst. The nematocyst is surrounded by a fibrillar system of microtubules and microfilaments that terminate in hemidesmosomal processes which anchor the nematocyst to the acellular mesoglea of the tentacle.