Observations on the anatomy and behaviour of the cubozoan Carybdea rastonii haacke

The cubozoan Carybdea rastonii occurs throughout the Pacific and is very abundant in areas of South Australia. C. rastonii has been observed feeding in the field on mysids and larval fish and on Anemia and fish in the laboratory. The medusae occur in swarms and are closely associated with sand patches during the day (but are not capable of attachment like C. sivickisi) and move up to the surface at dawn and dusk. The species is dioecious and the males secrete a sperm strand that may be picked up by the female. This study provides some preliminary observations on the behaviour and ecology of the cubomedusan Carybdea rastonii to stimulate further research on the mechanisms of sensory perception within the order Cubozoa. Observations on the nematocysts and the optic system are presented along with field and laboratory observations on anatomy and behaviour. The evidence for the role of vision in cubozoan behaviour is discussed.     

Ocean acidification alters zooplankton communities and increases top‐down pressure of a cubozoan predator

The composition of local ecological communities is determined by the members of the regional community that are able to survive the abiotic and biotic conditions of a local ecosystem. Anthropogenic activities since the industrial revolution have increased atmospheric CO₂ concentrations, which have in turn decreased ocean pH and altered carbonate ion concentrations: so called ocean acidification (OA). Single‐species experiments have shown how OA can dramatically affect zooplankton development, physiology and skeletal mineralization status, potentially reducing their defensive function and altering their predatory and antipredatory behaviors. This means that increased OA may indirectly alter the biotic conditions by modifying trophic interactions. We investigated how OA affects the impact of a cubozoan predator on their zooplankton prey, predominantly Copepoda, Pleocyemata, Dendrobranchiata, and Amphipoda. Experimental conditions were set at either current (pCO₂ 370 μatm) or end‐of‐the‐century OA (pCO₂ 1,100 μatm) scenarios, crossed in an orthogonal experimental design with the presence/absence of the cubozoan predator Carybdea rastoni. The combined effects of exposure to OA and predation by C. rastoni caused greater shifts in community structure, and greater reductions in the abundance of key taxa than would be predicted from combining the effect of each stressor in isolation. Specifically, we show that in the combined presence of OA and a cubozoan predator, populations of the most abundant member of the zooplankton community (calanoid copepods) were reduced 27% more than it would be predicted based on the effects of these stressors in isolation, suggesting that OA increases the susceptibility of plankton to predation. Our results indicate that the ecological consequences of OA may be greater than predicted from single‐species experiments, and highlight the need to understand future marine global change from a community perspective.     

Variation in soft tissue chemistry among scyphozoan and cubozoan jellyfishes from the Great Barrier Reef,Australia

Bioaccumulation of trace elements in jellyfish has so far received little attention, despite their being prey for many animals from multiple trophic levels and targeted by commercial jellyfish fisheries. Scyphozoan and cubozoan jellyfish were collected over a three year period from across-shelf and along the northern and central Great Barrier Reef, Australia. To test the hypotheses that jellyfishes were able to accumulate elements above ambient background levels, and if there were spatial or temporal variations among species, soft tissue concentrations of 14 trace elements were compared with ambient seawater concentrations. Most elements, including aluminium, arsenic, barium, cadmium, chromium, copper, iron, manganese and zinc were measured at concentrations above ambient seawater levels indicating bioaccumulative capacity. Results showed some regulation of lithium in Cassiopea sp., Cyanea sp. and Mastigias sp., while calcium, magnesium and strontium reflected ambient conditions for all species. Accumulation varied significantly among species and sampling locations. For Mastigias sp. and Netrostoma sp., tissue concentrations of Al, As, Cu, Fe and Zn decreased with distance from the mainland. The hypothesis that jellyfishes are capable of accumulating trace elements was accepted, and their use as biomonitors should be investigated further.     

Abundance patterns of cubozoans on and near the Great Barrier Reef

The ecology of cubozoans is poorly understood and there are few quantitative studies on their distribution patterns. Sampling was designed to test first for variation in abundance with distance across the continental shelf in waters of the Great Barrier Reef, Australia. Second, we tested for the possible influence of islands versus submerged reefs on the abundances of cubozoan jellyfishes. Jellyfishes were collected after attraction to tethered night lights. Additional sampling focused on turbid near-shore waters. Carybdeid jellyfishes were found at mainland, inner, and mid-shelf reefs during summers between 2007 and 2010. No cubozoan medusae were found at outer reef sites. Copula sivickisi and Carukia barnesi were more abundant near reefs with islands than at fully submerged reefs. There was no evidence of lunar periodicity in abundance for these cubozoan taxa. Chironex fleckeri medusae were only found close to shore near the mainland, but they were rarely observed when riverine runoff was high. All taxa were characterized by high spatial and temporal variation and there was some evidence for small populations at spatial scales of less than one kilometer. “Blooms” and related intensity of predation and risk to humans are most likely at small spatial scales.     

Gonadal cnidocytes in the cubozoan Tripedalia cystophora Conant, 1897 (Cnidaria: Cubozoa)

Cubozoans have a complex lifecycle in many ways similar to the scyphozoan lifecycle. The sexual reproduction within cubozoans varies between species with one clade having copulation and internal fertilization and the release of planula larvae. This cubozoan clade, the family Tripedaliidae, includes three species, Copula sivickisi, Tripedalia cystophora, and Tripedalia binata. In a recent study, it was suggested that in C. sivickisi cnidocytes play a new and important role during the sexual reproduction. Male derived cnidocytes anchor sperm packages to the female gonads and female derived cnidocytes protect the externalized embryo strand. Here, we have examined the gonads and gametes of T. cystophora and our results reveal that the male produced spermatozeugmata have a high number of isorhiza type cnidocytes, which are transferred along with the sperm during copulation. This adds further support to our hypothesis that they are important for sperm anchorage. The female gonads are lacking cnidocytes all together showing that cnidocyte production is not just a default state of the epithelium in these animals.     

Observations on the anatomy,behaviour, reproduction and life cycle of the cubozoan Carybdea sivickisi

Substantial numbers of the very small carybdeid jellyfish, Carybdea sivickisi, have been observed feeding actively by divers in the vicinity of fringing coral reefs. During the day specimens were seen in close association with the substrate and with sessile macroalgae. They appeared able to adhere to substrates by contact with an area on the aboral surface of the bell. Individuals maintained in the laboratory showed the same adhering ability. The adhesive organs correspond to 4 areas of raised secretory epithelium on the aboral surface.Following capture, one isolated specimen extruded a long gelatinous strand containing several thousand developing embryos and numerous functional nematocysts. The embryos developed into characteristic cubozoan planulae, which were able to attach themselves temporarily to substrates by means of nematocysts. After 4 days of free swimming, planulae began to attach permanently and to develop into sessile polyps with 3 or 4 tentacles, each armed with a single stenotele.The species displays sexual dimorphism and evidence for spermatophore formation and transfer which parallel that reported for Tripedalia cystophora. The presence of sperm-storage sacs in both sexes, the production of an embryo mass, the adhering behaviour and an apparent association with algal substrates are among features apparently unique to the species.     

Origin and early diversification of the phylum Cnidaria Verrill: major developments in the analysis of the taxon's Proterozoic–Cambrian history

Diploblastic eumetazoans of the phylum Cnidaria originated during the Neoproterozoic Era, possibly during the Cryogenian Period. The oldest known fossil cnidarians occur in strata of Ediacaran age and consist of polypoid forms that were either nonbiomineralizing or weakly so. The oldest possible anthozoans, including the genus Ramitubus, may be related to tabulate corals and occur in the Doushantuo Lagerstätte (upper Doushantuo Formation, South China), the age of which is poorly constrained (approximately 585 Ma?). Conulariid scyphozoans may first appear as early as 635–577 Ma (Lantian Formation, South China). A definite conulariid, most similar to Palaeozoic species assigned to the genus Paraconularia, occurs in association with the possible scyphozoan, Corumbella werneri, in the latest Ediacaran (c. 543 Ma) Tamengo Formation of Brazil. Basal Cambrian (c. 540 Ma) phosphorites in the upper Kuanchuanpu Formation (South China) yield solitary polyps of the oldest probable anthozoan (Eolympia pediculata), which appears to have been a stem hexacorallian. This same formation contains fossils interpreted by some authors as pentaradial cubozoan polyps; however, both the oldest known cubozoans and the oldest hydrozoans, all medusae, may actually occur in the Cambrian (Series 3, c. 505 Ma) Marjum Formation (Utah, USA). Although these recently published palaeontological data tend to corroborate the hypothesis that Cnidaria has a relatively deep Neoproterozoic history, the timing of major internal branching events remains poorly constrained, with, for example, the results of some molecular clock analyses indicating that the two cnidarian subphyla (Anthozoaria and Medusozoa) may have originated as many as one billion years ago. Further progress towards elucidating the evolution and early fossil record of cnidarians may accrue from: (1) an intensive search for phosphatized soft parts in possible anthozoans from the Ediacaran Doushantuo Formation; (2) an expanded search for Ediacaran conulariids; and (3) additional detailed analyses of the taphonomy and preservation of Ediacaran and Cambrian cnidarians, including possible pentaradial cubozoan polyps from the Fortunian upper Kuanchuanpu Formation.     

Early Cambrian Pentamerous Cubozoan Embryos from South China

Background

Extant cubozoans are voracious predators characterized by their square shape, four evenly spaced outstretched tentacles and well-developed eyes. A few cubozoan fossils are known from the Middle Cambrian Marjum Formation of Utah and the well-known Carboniferous Mazon Creek Formation of Illinois. Undisputed cubozoan fossils were previously unknown from the early Cambrian; by that time probably all representatives of the living marine phyla, especially those of basal animals, should have evolved.

Methods

Microscopic fossils were recovered from a phosphatic limestone in the Lower Cambrian Kuanchuanpu Formation of South China using traditional acetic-acid maceration. Seven of the pre-hatched pentamerous cubozoan embryos, each of which bears five pairs of subumbrellar tentacle buds, were analyzed in detail through computed microtomography (Micro-CT) and scanning electron microscopy (SEM) without coating.

Results

The figured microscopic fossils are unequivocal pre-hatching embryos based on their spherical fertilization envelope and the enclosed soft-tissue that has preserved key anatomical features arranged in perfect pentaradial symmetry, allowing detailed comparison with modern cnidarians, especially medusozoans. A combination of features, such as the claustrum, gonad-lamella, suspensorium and velarium suspended by the frenula, occur exclusively in the gastrovascular system of extant cubozoans, indicating a cubozoan affinity for these fossils. Additionally, the interior anatomy of these embryonic cubozoan fossils unprecedentedly exhibits the development of many new septum-derived lamellae and well-partitioned gastric pockets unknown in living cubozoans, implying that ancestral cubozoans had already evolved highly specialized structures displaying unexpected complexity at the dawn of the Cambrian. The well-developed endodermic lamellae and gastric pockets developed in the late embryonic stages of these cubozoan fossils are comparable with extant pelagic juvenile cubomedusae rather than sessile cubopolyps, whcih indicates a direct development in these fossil taxa, lacking characteristic stages of a typical cnidarian metagenesis such as planktonic planula and sessile polyps.     

Meteorona kishinouyei,a new family,genus and species (Cnidaria,Cubozoa, Chirodropida) from Japanese Waters

A new family, genus and species of cubozoan box jellyfish belonging to the order Chirodropida is reported from the eastern Japan. Meteorona kishinouyei gen. et sp. n. possesses the following unique morphological characters with respect to other known species in the Chirodropida: having one tentacle per scalpel-like unbranched pedalium and slightly raised unbranched gastric saccules. A comparative table of the primary diagnostic characters of genus and order in the Chirodropida is given. The order Chirodropida is redefined. The family Chiropsellidae is established. Discussion is provided on the implications for these findings on our current understanding of Cubozoan systematics.     

Phospholipase A2 in cnidaria

Phospholipase A2 (PLA2) is an enzyme present in snake and other venoms and body fluids. We measured PLA2 catalytic activity in tissue homogenates of 22 species representing the classes Anthozoa, Hydrozoa, Scyphozoa and Cubozoa of the phylum Cnidaria. High PLA2 levels were found in the hydrozoan fire coral Millepora sp. (median 735 U/g protein) and the stony coral Pocillopora damicornis (693 U/g) that cause skin irritation upon contact. High levels of PLA2 activity were also found in the acontia of the sea anemone Adamsia carciniopados (293 U/g). Acontia are long threads containing nematocysts and are used in defense and aggression by the animal. Tentacles of scyphozoan and cubozoan species had high PLA2 activity levels: those of the multitentacled box jellyfish Chironex fleckeri contained 184 U/g PLA2 activity. The functions of cnidarian PLA2 may include roles in the capture and digestion of prey and defense of the animal. The current observations support the idea that cnidarian PLA2 may participate in the sting site irritation and systemic envenomation syndrome resulting from contact with cnidarians.     

Calcium sulfate hemihydrate (bassanite) statoliths in the cubozoan Carybdea sp.

The chemistry and physical structure of statoliths of young cubozoan medusae (Carybdea sp.) were examined by X-ray spectroscopy (EDX) and X-ray powder diffractometry (XRD). These concretions, associated with sensory receptors, were found to consist of bassanite (calcium sulfate hemihydrate), a dense but hygroscopic biomineral. Bassanite occurs in a cluster of radially oriented crystals in a druse, which contains perfect hexagonal crystals. This discovery provides evidence that the Rhopaliophora (Scyphozoa and Cubozoa) originated from an ancestor having statoliths of bassanite.     

The structure and function of the nematocysts of Chironex fleckeri Southcott, 1956

Cell and Tissue Research - Microbasic p-mastigophores, euryteles of two size groups, holotrichous isorhizas and atrichous isorhizas, comprise the cnidom of Chironex fleckeri, a cubozoan that has...     

Anatomy and affinities of a new 535‐million‐year‐old medusozoan from the Kuanchuanpu Formation,South China

We describe here Sinaster petalon gen. et sp. nov., a new embryonic form from the c. 535 million‐year‐old Kuanchuanpu Formation of South China (Ningqiang, Shaanxi Province). The excellent three‐dimensional, phosphatic preservation of these microfossils allowed us to use x‐ray microtomographic techniques to make accurate reconstructions of their internal structures and to compare their anatomy point‐by‐point with that of extant cnidarians and other animal groups. Sinaster petalon has anatomical features typical of extant Medusozoa (Cnidaria), such as coronal muscles, perradial and adradial frenula, interradial septa, accessory septa, gonad‐lamellae, tentacle buds and perradial pockets. Although Sinaster cannot be straightforwardly assigned to any crown‐group within Medusozoa, the presence of marginal lappets and endodermal lamellae suggests that it is closer to Cubozoa and Scyphozoa than to any other group of modern cnidarians. The tentative placement of Sinaster within the stem‐group Cubozoa is justified by the presence of a velarium supported by a frenulum. The cubozoan affinities of Sinaster are also supported by cladistic analysis.     

Cilium evolution: identification of a novel protein, nematocilin, in the mechanosensory cilium of Hydra nematocytes

The cnidocil at the apical end of Hydra nematocytes is a mechanosensory cilium, which acts as a "trigger" for discharge of the nematocyst capsule. The cnidocil protrudes from the center of the cnidocil apparatus and is composed of singlet and doublet microtubules surrounding an electron-dense central filament. In this paper, we identify a novel protein, nematocilin, which is localized in the central filament. Immunofluorescence staining and immunogold electron microscopy show that nematocilin forms filaments in the central core of the cnidocil. Nematocilin represents a new member of the intermediate filament superfamily. Two paralogous sequences of nematocilin are present in the Hydra genome and appear to be the result of recent gene duplication. Comparison of the exon-intron structure suggests that the nematocilin genes evolved from the nuclear lamin gene by conserving exons encoding the coiled-coil domains and replacing the C-terminal lamin domains. Molecular phylogenetic analyses also support the hypothesis of a common ancestor between lamin and nematocilin. Comparison of cnidocil structures in different cnidarians indicates that a central filament is present in the cnidocils of several hydrozoan and a cubozoan species but is absent in the cnidocils of anthozoans. A nematocilin homolog is absent in the recently completed genome of the anthozoan Nematostella. Thus, the evolution of a novel ciliary structure, which provides mechanical rigidity to the sensory cilium during the process of mechanoreception, is associated with the evolution of a novel protein.     

Comparison of the Esterases and Acid Phosphatases in Paramecium multimicronucleatum,Syngens 1–5, P. jenningsi,P. caudatum,and the P. aurelia Complex1

ABSTRACT. Forty-eight stocks in Paramecium jenningsi, syngens 1–5 of P. multimicronucleatum, P. caudatum, P. primaurelia, P. biaurelia, and P. tetraurelia were grown axenically and tested for their esterases and acid phosphatases using starch gel electrophoresis. The five esterases and the acid phosphatases previously characterized in species of the P. aurelia complex were also found in P. jenningsi, and three to four of the esterases and the acid phosphatases were found in the P. multimicronucleatum species complex and in P. caudatum. Additional subtypes were observed for each of the enzyme phenotypes in these new (though here unnamed) species of Paramecium. Two of the new acid phosphatase subtypes, which depart radically in mobility and in pattern, were found in syngen 3 of P. multimicronucleatum and in P. caudatum. Except for syngens 1 and 5 in P. multimicronucleatum, the degree of similarity between syngens 1, 5 and 2, 3, and 4 appears to be very low—perhaps even lower than that seen for species in the aurelia complex. More realistically, the syngens of P. multimicronucleatum should be considered as separate species although they are not here given separate taxonomic names. Limited sharing of subtypes occurred between species in different species complexes. This observation suggests that the molecular distances between species complexes may be even greater than between species within a complex.     

Phylogeny of Medusozoa and the evolution of cnidarian life cycles

To investigate the evolution of cnidarian life cycles, data from the small subunit of the ribosome are used to derive a phylogenetic hypothesis for Medusozoa. These data indicate that Cnidaria is monophyletic and composed of Anthozoa and Medusozoa. While Cubozoa and Hydrozoa are well supported clades, Scyphozoa appears to be paraphyletic. Stauromedusae is possibly the sister group of either Cubozoa or all other medusozoans. The phylogenetic results suggest that: the polyp probably preceded the medusa in the evolution of Cnidaria; within Hydrozoa, medusa development involving the entocodon is ancestral; within Trachylina, the polyp was lost and subsequently regained in the parasitic narcomedusans; within Siphonophorae, the float originated prior to swimming bells; stauromedusans are not likely to be descended from ancestors that produced medusae by strobilation; and cubozoan polyps are simplified from those of their ancestors, which possessed polyps with gastric septa and four mesogleal muscle bands and peristomial pits.     

Karyotypic analysis of Cajanus,Atylosia, and Rhynchosia species

Summary Somatic chromosomes of two cultivais of Cajanus cajan, eight species of Atylosia (A. albicans, A. cajanifolia, A. lineata, A. platycarpa, A. scarabaeoides, A. serica, A. trinervia and A. volubilis), and of Rhynchosia rothii were analysed. All species had 2n=22. Eight of the 10 species studied had two pairs of satchromosomes while A. scarabaeoides and A. sericea had only one sat-chromosome pair. Based on relative chromosome length (L%), arm ratio (pa-value) and presence or absence of secondary constriction, a karyotype formula for each species was formulated. Based on these parameters the chromosome pairs could also be assigned to groups ranging from 8 to 10 in different species. Except for the asymmetrical karyotype of A. albicans, the other species had rather moderately symmetrical karyotypes.