Photoreceptors of cubozoan jellyfish

The anatomically sophisticated visual system of the cubozoan jellyfish Carybdea marsupialis is described. Individual cubomedusae have eight complex eyes, each with a cornea, lens, and retina of ciliated photoreceptor cells, eight slit ocelli, and eight dimple ocelli. The photoreceptor cells of the complex eyes are bipolar and resemble vertebrate rod cells. Each photoreceptor has an outer cylindrical light-receptive segment that projects into a vitreous space that separates the lens and the retina, an inner segment rich in pigment granules, and a basal region housing the nucleus. The outer segment is a modified cilium with a 9 + 2 arrangement of microtubules plus stacks of membrane. These stacks of membrane form numerous discs that are oriented transversely to the long axis of the cell. The outer segment is connected to the inner segment by a slender stalk. The basal end of each photoreceptor forms an axon that projects into an underlying layer of interneurons. Each ocellus is composed of ciliated photoreceptor cells containing pigment granules. Rhodopsin-like and opsin-like proteins are found in the membrane stacks of the outer segments of the photoreceptors of the complex eyes. An ultraviolet-sensing opsin-like protein is present in the inner segments and basal regions of some of the photoreceptors of the complex eyes. Rhodopsin-like proteins are also detected in the photoreceptors of the slit ocelli. The cellular lens, composed of crystallin proteins, shows a paucity of organelles and a high concentration of homogeneous cytoplasm. Neurons expressing RFamide (Arg-Phe-amide) comprise a subset of interneurons found beneath the retinas of the complex eyes. RFamide-positive fibers extend from these neurons into the stalks of the rhopalia, eventually entering into the subumbrellar nerve ring. Vision may play a role in the navigation, feeding, and reproduction of the cubomedusae.     

Rhopalia are integrated parts of the central nervous system in box jellyfish

In cubomedusae, the central nervous system (CNS) is found both in the bell (the ring nerve) and in the four eye-bearing sensory structures (the rhopalia). The ring nerve and the rhopalia are connected via the rhopalial stalks and examination of the structure of the rhopalial stalks therefore becomes important when trying to comprehend visual processing. In the present study, the rhopalial stalk of the cubomedusae Tripedalia cystophora has been examined by light microscopy, transmission electron microscopy, and electrophysiology. A major part of the ring nerve is shown to continue into the stalk and to contact the rhopalial neuropil directly. Ultrastructural analysis of synapse distribution in the rhopalial stalk has failed to show any clustering, which indicates that integration of the visual input is probably spread throughout the CNS. Together, the results indicate that cubomedusae have one coherent CNS including the rhopalia. Additionally, a novel gastrodermal nerve has been found in the stalk; this nerve is not involved in visual processing but is likely to be mechanosensory and part of a proprioceptory system.This work was supported by grants 621-2002-4873 from the Swedish Research Council to D.-E. Nilsson and 21-2204-04 from the Danish Research Council to A. Garm.     

Growth and age determination of the tropical Australian cubozoan Chiropsalmus sp.

Chiropsalmus sp. medusae collected in this study ranged from 3 to 71 mm diagonal bell width and displayed growth best described by the following equation size (mm) = 74.9 × exp (−exp(0.041 (time since metamorphosis (day) −35.6674))). Growth rates of up to 7 mm week⁻¹ increase in diagonal bell width are theoretically possible, with animals able to reach sexual maturity in approximately 70 days. Correlation of the number of rings on the statoliths with the predicted age of the individual from the field produced a relationship that indicates the growth rings are laid down daily and as such could be used to infer age of the medusae. Over the 1998–1999 season, there were four influxes of juvenile cohorts, each occurring approximately 14 days after a major rainfall event.     

Irukandji jellyfish polyps exhibit tolerance to interacting climate change stressors

Increasing ocean temperatures and strengthening boundary currents have caused the poleward migration of many marine species. Cubozoan jellyfish known to cause Irukandji syndrome have historically been confined to tropical waters but may be expanding into subtropical regions. Here, we examine the interactive effects of warming and acidification on the population dynamics of polyps of an Irukandji jellyfish, Alatina nr mordens, and the formation of statoliths in newly metamorphosed medusae, to determine if this jellyfish could tolerate future conditions predicted for southeast Queensland (SEQ), Australia. Two experiments, examining the orthogonal factors of temperature and pH, were undertaken. Experiment 1 mimicked the current, ca. 2050 and ca. 2100 summer temperature and pH conditions predicted for SEQ using A1F1 scenarios (temperature: 25, 27, 29 °C; pH: 7.9, 7.8, 7.6) and Experiment 2 mimicked current and future winter conditions (18 and 22 °C, pH 7.9, 7.8, 7.6). All polyps in Experiment 1 survived and budded. Fewer polyps budded in the lower pH treatments; however, patterns varied slightly among temperature treatments. Statoliths at pH 7.6 were 24% narrower than those at pH 7.8 and 7.9. Most polyps survived the winter conditions mimicked by Experiment 2 but only polyps in the 22 °C, pH 7.9 treatment increased significantly. The current absence of A. nr mordens medusae in SEQ, despite the polyps' ability to tolerate the current temperature and pH conditions, suggests that ecological, rather than abiotic factors currently limit their distribution. Observations that budding was lower under low pH treatments suggest that rates of asexual reproduction will likely be much slower in the future. We consider that A. nr mordens polyps are likely to tolerate future conditions but are unlikely to thrive in the long term. However, if polyps can overcome potential ecological boundaries and acidification proceeds slowly A. nr mordens could expand polewards in the short term.     

Eight microsatellite loci for the Irukandji syndrome-causing carybdeid jellyfish, Carukia barnesi (Cubozoa, Cnidaria)

Microsatellites are high-resolution genetic markers that may be applied to examine parentage, population structure and the direction and extent of dispersal. Here we present eight polymorphic microsatellite loci developed for the carybdeid jellyfish, Carukia barnesi. The loci were developed from a microsatellite-enriched, partial genomic DNA library and tested for polymorphism on animals from each of two geographically distinct populations, Lizard Island and Double Island, from the Great Barrier Reef. The number of alleles observed for each locus ranged from 7 to 19.     

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.     

Cubozoan jellyfish envenomation syndromes and their medical treatment in northern Australia

The stings of Chironex fleckeri, Carukia barnesi and two unidentified carybdeids cause severe or fatal symptoms to swimmers in tropical Australia. The cubozoans and their envenomation syndromes are described. First-aid and medical treatment are reviewed, and safety precautions to prevent envenomation are recommended.     

Some implications of molecular phylogenetics for understanding biodiversity in jellyfishes,with emphasis on Scyphozoa

Statistical phylogenetic analyses of 111 5.8S and partial-28S ribosomal DNA sequences (total aligned length=434 nucleotides) including jellyfishes representing approximately 14 of known scyphozoan morphospecies (21 genera, 62 families, and 100 orders) are presented. These analyses indicate stauromedusae constitute a fifth cnidarian class (Staurozoa) basal to a monophyletic Medusozoa (=Cubozoa, Hydrozoa, and Scyphozoa). Phylogenetic relationships among the medusozoans are generally poorly resolved, but support is found for reciprocal monophyly of the Cubozoa, Hydrozoa, Coronatae, and Discomedusae (=Semaeostomeae + Rhizostomeae). In addition, a survey of pairwise sequence differences in Internal Transcribed Spacer One within morphospecies indicates that scyphozoan species diversity may be approximately twice recent estimates based on morphological analyses. These results highlight difficulties with traditional morphological treatments including terminology that obfuscates homologies. By integrating molecular phylogenetic analyses with old and new morphological, behavioural, developmental, physiological, and other data, a much richer understanding of the biodiversity and evolution of jellyfishes is achievable.     

Immunohistochemical evidence for multiple photosystems in box jellyfish

Cubomedusae (box jellyfish) possess a remarkable visual system with 24 eyes distributed in four sensory structures termed rhopalia. Each rhopalium is equipped with six eyes: two pairs of pigment cup eyes and two unpaired lens eyes. Each eye type probably captures specific features of the visual environment. To investigate whether multiple types of photoreceptor cells are present in the rhopalium, and whether the different eye types possess different types of photoreceptors, we have used immunohistochemistry with a range of vertebrate opsin antibodies to label the photoreceptors, and electroretinograms (ERG) to determine their spectral sensitivity. All photoreceptor cells of the two lens eyes of the box jellyfish Tripedalia cystophora and Carybdea marsupialis displayed immunoreactivity for an antibody directed against the zebrafish ultraviolet (UV) opsin, but not against any of eight other rhodopsin or cone opsin antibodies tested. In neither of the two species were the pigment cup eyes immunoreactive for any of the opsin antibodies. ERG analysis of the Carybdea lower lens eyes demonstrated a single spectral sensitivity maximum at 485 nm suggesting the presence of a single opsin type. Our data demonstrate that the lens eyes of box jellyfish utilize a single opsin and are thus color-blind, and that there is probably a different photopigment in the pigment cup eyes. The results support our hypothesis that the lens eyes and the pigment cup eyes of box jellyfish are involved in different and specific visual tasks.