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Ctenophores are descendants of an early branching basal metazoan lineage, which may have evolved neurons and muscles independently from other animals. Mnemiopsis is one of the important reference ctenophore species. However, little is known about its neuromuscular organization. Here, we mapped and tracked the development of the neural and muscular elements in the early hatching cydippid larvae, as well as adult Mnemiopsis leidyi. The overall development of the neuromuscular system in Mnemiopsis was very similar to Pleurobrachia bachei, although in Mnemiopsis the entire process occurred significantly faster. The subepithelial neural cells were observed immediately after hatching. This population consisted of a dozen of separated individual neurons with short neurites. In about 2 days, when their neurites grew significantly longer and connected to their neighbors, they began to form a canonical polygonal subepithelial network. Mesogleal neural elements prominent in all studied adult ctenophores were not detectable in Mnemiopsis larvae but were clearly labeled in closely related Lobata species Bolinopsis infundibulum. Hatched larvae also had putative mechanoreceptors with long stereocilia and approximately two dozen muscle cells. In adult Mnemiopsis, the feeding lobes and auricles contained two distinct populations of neurons and neural ensembles that were not observed in other ctenophore lineages and likely represented elaborate neuronal innovations characteristic for the clade Lobata and their lifestyles.

The IS630/Tc1/mariner superfamily of transposable elements (TE) is one of the most numerous and widespread among DNA transposons. The IS630/Tc1/mariner TE are divided into eight families: IS630, Tc1, mariner, pogo, maT, mosquito, plants, and rosa. The members of the rosa family (DD41D transposons) were allocated to a separate group relatively recently and are currently characterized in detail only in insects. It is known that the rosa family includes the Crmar-like and LTIR subfamilies. In the present work, the DD41D transposons were for the first time described in Mnemiopsis leidyi and Pleurobrachia bachei ctenophores. It was established that the elements of Mnemiopsis represent a new group, previously unknown, which we named leidyi. The members of this subfamily combine the traits inherent to two other subfamilies of DD41D transposons. The rosa elements belonging to the LTIR subfamily and having more extended DDE/D domains were detected in P. bachei.

Ctenophores are a group of largely-planktonic, gelatinous carnivores whose most common method of prey capture is nearly a phylum-defining trait. Tentaculate ctenophores release an unknown proteinaceous adhesive from specialised colloblast cells lining their tentacles following prey contact with the tentacles. There exist no extant studies of the mechanical properties of colloblast adhesive. We use live microscopy techniques to visualise adhesion events between Pleurobrachia pileus colloblasts and probes of different surface chemistries in response to probing with varying contact areas. We further define two mechanisms of adhesion termination upon probe retraction. Adapting a technique for measuring surface tension, we examine the adhesive strength of tentacles in the ctenophore Pleurobrachia bachei under varying pH and bonding time conditions, and demonstrate the destructive exhaustion of colloblast adhesive release. We find that colloblast-mediated adhesion is rapid, and that the bonding process is robust against shifts in ambient pH. However, we find that the Pleurobrachia colloblast adhesive system is among the weakest biological adhesive systems yet described. We place this surprising observation into a broader ecophysiological context by modeling prey capture for prey of a range of sizes. We find that limited use of colloblast adhesive with high surface area contact is suitable both for capturing appropriately sized prey and rejecting, by detachment, prey above a certain size threshold. This allows Pleurobrachia, lacking a mechanism to directly “see” potential prey they are interacting with, to invest in capturing only prey of an appropriate size, decreasing the risk of injury.Summary statementCtenophore colloblast adhesive is found to be strong, but few colloblasts are simultaneously active, producing a weakly-adhering system. A physical model demonstrates how such a system may filter unsuitable prey.

Microplastic (MP) ingestion has been widely recorded in aquatic organisms, but few studies focus on cnidarians and ctenophores, which form a significant contribution to marine trophic interactions. Scyphozoans (Cyanea capillata, C. lamarckii and Aurelia aurita), hydrozoan (Cosmetira pilosella) and ctenophores (Beroe cucumis and Pleurobrachia bachei) collected opportunistically from Orkney, Shetland and the North Sea were thermally disintegrated, with a subsample of ingested plastics analysed using FTIR. A total of 1,986 MPs were counted (94% fibres), the majority (84.4%) in the four cnidarian species. Highest MP concentrations were recorded in B. cucumis (0.956 ml-1), whilst C. pilosella yielded the lowest (0.014 ml-1). The main polymers in digestate were PET and PP, with 27% discounted as non-plastics. In feeding trials, A. aurita ingested a greater quantity of PET fibres (60-80%), compared to nylon (0%) and HDPE fibres (0%). This study demonstrates cnidarians and ctenophores, a largely overlooked group, are a potential route for MPs entry into food webs.

Enigmatic ctenophores are descendants of one of the earliest branching metazoan lineage. Their nervous systems are equally elusive. The lack of convenient neurogenic molecules and neurotransmitters suggests an extensive parallel evolution and independent origins of neurons and synapses. However, the field is logged behind due to the lack of microanatomical data about the neuro-muscular systems in this group of animals. Here, using immunohistochemistry and scanning electron microscopy, we describe the organization of both muscular and nervous systems in the sea gooseberry, Pleurobrachia bachei, from North Pacific. The diffused neural system of Pleurobrachia consists of two subsystems: the subepithelial neural network and the mesogleal net with about 5000-7000 neurons combined. Our data revealed the unprecedented complexity of neuromuscular organization in this basal metazoan lineage. The anatomical diversity of cell types includes at least nine broad categories of neurons, five families of surface receptors and more than two dozen types of muscle cells as well as regional concentrations of neuronal elements to support ctenophore feeding, complex swimming, escape and prey capture behaviors. In summary, we recognize more than 80 total morphological cell types. Thus, in terms of cell type specification and diversity, ctenophores significantly exceed what we currently know about other prebilaterian groups (placozoan, sponges, and cnidarians), and some basal bilaterians.

Ctenophores are descendants of one of the earliest branching metazoan lineage with enigmatic nervous systems. The lack of convenient neurogenic molecules and neurotransmitters suggests an extensive parallel evolution and independent origins of neurons and synapses. However, the field lags due to the lack of microanatomical data about the neuro-muscular systems in this group of animals. Here, using immunohistochemistry and scanning electron microscopy, we describe the organization of both muscular and nervous systems in the sea gooseberry, Pleurobrachia bachei, from North Pacific. The diffuse neural system of Pleurobrachia consists of two subsystems: the subepithelial neural network and the mesogleal net with about 5,000-7,000 neurons combined. Our data revealed the unexpected complexity of neuromuscular organization in this basal metazoan lineage. The anatomical diversity of cell types includes at least nine broad categories of neurons, five families of surface receptors and more than two dozen types of muscle cells as well as regional concentrations of neuronal elements to support ctenophore feeding, complex swimming, escape, and prey capture behaviors. In summary, we recognize more than 80 total morphological cell types. Thus, in terms of cell-type specification and diversity, ctenophores significantly exceed what we currently know about other prebilaterian groups (placozoan, sponges, and cnidarians), and some basal bilaterians.

The mitochondrial genomes in ctenophores are among the most compact in the animal kingdom with multiple rearrangements and examples of gene loss. Here, by resequencing of the Pleurobrachia bachei mitochondrial genome, we show that the high level of polymorphism (>10%) in Pleurobrachia might contribute to the ongoing fast evolution of ctenophores including the presence of truncated versions of apparently canonical genes such as cox1. Second, the codon interpretations in ctenophores, without robust proteomic data related to mitochondrial genes, is still a challenging issue, which is open for future experimental analyses.

The phylogenetic position of the phylum Ctenophora and the nature of ctenphore nervous systems are highly debated topics in modern evolutionary biology. However, very little is known about the organization of ctenophore neural and muscular systems, and virtually nothing has been reported about their embryogenesis. Here we have characterized the neural and muscular development of the sea gooseberry, Pleurobrachia bachei, starting from the cleavage stages to posthatching larvae. Scanning electron microscopy and immunochemistry were used to describe the formation of the embryonic mouth, tentacles, combs, aboral organ, and putative sensory cells. The muscles started their specification at the end of the first day of Pleurobrachia development. In contrast, neurons appeared 2 days after myogenesis, just before the hatching of fully formed cydippid larvae. The first tubulin-immunoreactive neurons, a small group of four to six cells with neuronal processes, was initially recognized at the aboral pole during the third day of development. Surprisingly, this observed neurogenesis occurred after the emergence of distinct behavioral patterns in the embryos. Thus, the embryonic behavior associated with comb cilia beatings and initial muscle organization does not require morphologically defined neurons and their elongated neurites. This study provides the first description of neuromuscular development in the enigmatic ctenophores and establishes the foundation for future research using emerging genomic tools and resources.

Pleurobrachia bachei A. Agassiz, 1860 Synonyms in the area: Pleurobrachia pileus ���Palma 1971,1994; Palma & Meruane 1975; Palma & Rosales 1995; Pleurobrachia sp.���Pag��s et al. 2001. Remarks: the species was recorded off Valparaiso region (33��S) as Pleurobrachia pileus by Palma (1971, 1994), Palma & Meruane (1975), and Palma & Rosales (1995). Moreover, the species reported as Pleurobrachia sp. from off Antofagasta by Pag��s et al. (2001) is considered here as the same species. Distribution in South America: Pacific Ocean, Peru to Chile, from 3��S to 47��S (Palma 1971, 1994; Palma & Meruane 1975; Palma & Rosales 1995; Pag��s et al. 2001; Palma & Apablaza 2004; Pavez et al. 2006, 2010; and specimens collected in this study). Habitat: epipelagic species, very abundant in coastal waters (Palma & Rosales 1995; Palma & Apablaza 2004)., Published as part of M. P. Oliveira 1,16, S P. Miranda 2, *,, Es W. Mianzan 10,, Ro E. Migotto 11,, Ne B. Nascimento 2,11, Eli Nogueira J��nior 12,, Er Qui��ones 13,, Izio Scarabino 14,, T��n Schiariti 10,, Io N. Stampar 15,, Tronolone 2, , Qu��ria B. & Onio C. Marques 2,11, 2016, Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters, pp. 1-256 in Zootaxa 4194 (1) on page 214, DOI: 10.11646/zootaxa.4194.1.1

) nearshore,characteristics of upwelling conditions in eastern boundary regions, occurredthroughout the cruise. Two groups of gelatinous carnivorous zooplankton wereidentified associated with the density front structure: one located coastward fromthe front (Sphaeronectes gracilis, Euphysa aurata and Beroe cucumis) and another locatedseaward from the front (Liriope tetraphylla, Pleurobrachia bachei, Abylopsis tetragona andThalassocalyce inconstans). The most abundant species occurred more frequently inwell-oxygenated waters; however, high abundances (10–100 ind. 100 m

To estimate the predation effect of the predominant ctenophore Pleurobrachia bachei on the small-copepod community in the upwelling area off Mejillones (23° S), northern Chile, a series of oceanographic cruises and predation experiments were conducted in the austral springs 2000, 2001 and 2002. The daily consumption rates and predatory effect of P. bachei on the small copepods (in terms of % of standing stock and biomass removed daily) were determined at three stations located in relation to the shelf-break (coastal, shelf-break and oceanic) reaching values up to 4.5% per day of the

Ctenophores are important members of planktonic communities that are often abundant in dysaerobic environments. Previous studies have shown that ctenophores are not adversely affected by extended periods of hypoxia. The three species used in this study, Pleurobrachia bachei, Bolinopsis infundibulum, and Mnemiopsis leidyi, were all able to oxyregulate to very low partial pressures of oxygen (PO2s). These species were found to have mean critical oxygen tensions of 7.7, 10.6, and 7.2 hPa respectively. In general, ctenophores are better oxyregulators than medusae and many species of shrimps, fish and squid. Intragel oxygen was measured using a fibre optic oxygen optode. All these ctenophores have intragel subsurface [O2]s of 5–10% below that of the surrounding seawater. Intragel oxygen measurements of P. bachei showed a gradient of decreasing PO2 from surface tissues to the gut. Specimens of P. bachei over 14 mm in diameter had anaerobic guts. Survival times in anoxia ranged from 0 h for M. leidyi to up to 6 h for P. bachei. Ctenophores rely on aerobic metabolism to tolerate hypoxia.

Macrozooplankton and micronekton are intermediaries linking lower trophic levels (e.g., phytoplankton and mesozooplankton) to higher ones (e.g., fishes and birds). These organisms have not been extensively studied in the San Francisco Estuary (SFE), California. The objective of this study was to determine the distribution and abundance of macrozooplankton and micronekton in the SFE and to describe how these vary seasonally, interannually, and regionally in relation to environmental variables. Water column macrozooplankton and micronekton were sampled monthly from September 1997 to December 2000 at 6 stations spanning North, Central, and South Bays using a Methot Trawl. The macrozooplankton and micronekton in the lower SFE were dominated by 4 fishes and 7 invertebrates that comprised 98% of the total catch. Correspondence analyses revealed 4 groups of species that exhibited similar patterns of distri- bution and abundance. The assemblages changed between the wet and dry seasons and with distance from the coastal ocean. Based on abundance patterns, the dominant taxa in the lower SFE can be classified as: organisms spawned from common members of neritic assemblages that use mostly North Bay and that are abundant during the dry season (Clupea pallasi, Spirinchus thaleichthys, Porichthys notatus); estuarine-dependent organisms with broad distributions in the estuary year-round (Crangon franciscorum, Crangon nigricauda, Engraulis mordax); resident species remaining within the estuary but occurring mostly in South Bay during the wet season (Palaemon macrodactlyus, Synidotea laticauda, Neomysis kadi- akensis); and gelatinous species (Pleurobrachia bachei, Polyorchis spp.) occurring in all three bays with a single peak in abundance in December and January in North and South Bays. The variation in distribution, abundance, and composition of macrozooplankton and micronekton was related to life history strategies, distance from the coastal ocean, and season.

Here, we report on the impact of formalin preservation on the physical dimensions of the tentaculate ctenophore Pleurobrachia bachei A. Agassiz collected in the North East Pacific Ocean. Contrary to previously published papers [Oorthuyzen, W., Sadee, C., 1982. Voorkomen en groei van Pleurobrachia pileus en Aurelia aurita in de westelijke Wadddenzee en hun mogelijke rol als predator van platvislarven. Netherlands Institute of Sea Research, Texel; Yip, 1982. A note on the effect of preserving ctenophores in formaldehyde–seawater. Ir. Nat. J. 20 416–419] where a standard 20% shrinkage was applied to whole populations, we found that shrinkage rates are not constant and vary widely with the size of the specimen. A size reduction of 5–80% was observed in individuals ranging from 23 to 5 mm in boreal diameter when alive. The relationship between dry weight (DW) and length is also affected by the preservation process. Previously published biomass data and physiological rates based on preserved samples should therefore be re-examined when population was largely dominated by small size individuals.

The origins of neural systems remain unresolved. In contrast to other basal metazoans, ctenophores (comb jellies) have both complex nervous and mesoderm-derived muscular systems. These holoplanktonic predators also have sophisticated ciliated locomotion, behaviour and distinct development. Here we present the draft genome of Pleurobrachia bachei, Pacific sea gooseberry, together with ten other ctenophore transcriptomes, and show that they are remarkably distinct from other animal genomes in their content of neurogenic, immune and developmental genes. Our integrative analyses place Ctenophora as the earliest lineage within Metazoa. This hypothesis is supported by comparative analysis of multiple gene families, including the apparent absence of HOX genes, canonical microRNA machinery, and reduced immune complement in ctenophores. Although two distinct nervous systems are well recognized in ctenophores, many bilaterian neuron-specific genes and genes of 'classical' neurotransmitter pathways either are absent or, if present, are not expressed in neurons. Our metabolomic and physiological data are consistent with the hypothesis that ctenophore neural systems, and possibly muscle specification, evolved independently from those in other animals. This work was supported by NSF (NSF-0744649 and NSF CNS-0821622 to L.L.M.; NSF CHE-1111705 to J.V.S.), NIH (1R01GM097502, R01MH097062, R21RR025699 and 5R21DA030118 to L.L.M.; P30 DA018310 to J.V.S.; R01 AG029360 and 1S10RR027052 to E.I.R.), NASA/nNNX13AJ31G (to K.M.H., L.L.M. and K.M.K.), NSERC 458115 and 211598 (J.P.R.), University of Florida Opportunity Funds/McKnight Brain Research and Florida Biodiversity Institute (L.L.M.), Rostock Inc./A.V. Chikunov (E.I.R.), grant from Russian Federation Government 14.B25.31.0033 (Resolution No.220) (E.I.R.). F.A.K., I.S.P. and R.D.were supported by HHMI(55007424),EMBO and MINECO(BFU2012-31329 and Sev-2012-0208). Contributions of AU Marine Biology Program 117 and Molette laboratory 22.

The potential for competition for food among zooplanktivorous species of gelatinous zooplankton and fishes has been the subject of much speculation. Here, we evaluate the dietary over- laps among 2 scyphomedusan species, Aurelia labiata and Cyanea capillata, 1 ctenophore species, Pleurobrachia bachei, 1 hydromedusan species, Aequorea aequorea var. albida, and juveniles (Age-0) of 4 forage fish species, walleye pollock Theragra chalcogramma, Pacific sandlance Ammodytes hexapterus, Pacific herring Clupea pallasi, and pink salmon Oncorhynchus gorbuscha. Zooplankton samples collected in July-August 1995 to 1998 showed great similarity among years (86 to 96%), which allowed valid dietary comparisons between pelagic coelenterates and fishes col- lected in different years during that period. The predators fell into 2 groups, one that ate primarily crustacean prey (A. labiata, P. bachei, juvenile walleye pollock, sandlance, and herring), and another that ate mostly larvaceans (C. capillata, A. aequorea, and juvenile pink salmon). Species within the first group showed significant positive selection for crustacean prey and significant negative selec- tion for larvaceans. The opposite trends were observed in the second group. Dietary overlaps were higher among crustacean-eating species (63 ± 13%) and larvacean-eating species (66 ± 10%) than when comparing crustacean- with larvacean-eating species (24 ± 14%). Dietary overlaps among pelagic coelenterate species (41 ± 21%) and among fish species (42 ± 25%) were similar, while over- laps between pelagic coelenterate and fish species averaged 50 ± 21%. These pelagic coelenterate and fish species were collected together in 45 purse seine sets taken in Prince William Sound in July 1999. We conclude that the diets of pelagic coelenterate and forage fish species overlap substantially, and that the species co-occur spatially and temporally. Therefore, the potential for competition for prey exists for these zooplanktivores in Prince William Sound.

Target strengths were determined for individual Aequorea victoria and Pleurobrachia bachei using separate 200, 420 and 1,000 kHz transducers in an enclosure deployed off the dock of the Friday Harbor Laboratories in northern Puget Sound, Washington, USA. The target strength for Aequorea, when averaged over all animal sizes and all three trnasducer frequencies, was −72.6 dB. The target strength for Pleurobrachia was −75.9 dB when similarly averaged. Average reduced target strengths for Aequorea and Pleurobrachia were −43.3 and −33.1 dB, respectively. Differences in the sound scattering contrasts for Pleurobrachia and Aequorea are proposed to explain the larger reduced target strength of Pleurobrachia, relative to that of Aequorea. A new sound scattering model was developed to predict the backscattering cross-section of Aequorea. The model takes into account expected variations in target strength due to changes in shape of the jellyfish as it propels itself through the water. The scattering model was tuned specifically for Aequorea in the present study, but has a general formulation that is widely applicable to any medusa-shaped gelatinous zooplankter.

We propose a new approach to assess the predatory impact of gelatinous zooplankton on their prey, in which information from field samples and laboratory experiments allows us to estimate predator ingestion rates from analyses of predator gut contents. The feasibility of this approach was tested in laboratory experiments with the ctenophore Pleurobrachia bachei feeding on adult stages of the copepods Pseudocalanus newmani and Acartia longiremis. We developed a simple model of predator ingestion-egestion dynamics. The model assumes that predator clearance rates, F, and instantaneous egestion rates, c, are constant over the range of prey concentrations appropriate to the field study. A series of experiments was designed to test the validity of these assumptions and to estimate values of the parameters F and E for Pleurobrachia feeding on Pseudocalanus and Acartia. Results from these experiments indicate that the above assumptions are reasonable for these predator-prey pairs until prey concentrations exceed 60,000 prey m- 3. Ingestion rates are shown to be proportional to predator gut contents, with the slope of the relationship providing an estimate of the instantaneous egestion rate. Provided that the model assumptions are met, this approach can be used to estimate the predatory impact of other planktivorous predators on more complex prey assemblages.

Oodiniurn sp., an ectoparasitic oodinid dinoflagellate that closely resembles Oodinium jordani McLean & Nielsen, 1989 described from Sagitta elegans Verrill, 1873 (Phylum Chaetognatha), has been seen to parasitize Beroe abyssjcola Mortensen, 1927, Bolinopsis ?infundibulum (0. F . Miiller, 1776), Euplokamis dunlapae Mills, 1987, Dryodora glandiformis (Mertens, 1833), and Pleurobrachia bachei A. Agassiz, 1860, which represent 3 orders of the phylum Ctenophora, and the hydromedusa Euphysa sp. (phylum Cnidaria) in marine waters of the San Juan Archipelago, Washington State, USA. Up to several hundred trophozoites may be found on a single ctenophore, although most ctenophore hosts carry less than 50; the hydromedusa never carried more than 4. The parasites occurred on their ctenophore and medusan hosts from late October through early April, and not in the warmer months. These are the first reported instances of parasitism by a dinoflagellate on the Ctenophora, and by an Oodinium on the Cnidaria.

Seasonal abundance and vertical distribution of the carnivorous gelatinous zooplankton in an upwelling area of the northern Humboldt Current System ABSTRACT. The seasonal abundance and vertical distribution of gelatinous zooplankton collected during four cruises off Mejillones bay were analyzed. In this area we identified 44 species of macroplankton distributed in 23 siphonophores, 17 hydromedusae, and 4 ctenophores. Eight species, Sphaeronectes irregularis, Rhizophysa eysenhardti, Amphogona apicata, Proboscidactyla stellata, Sarsia coccometra, Pleurobrachia bachei, Thalassocalyce inconstans and Velamen parallelum, are the first records in the Humboldt Current System. The seasonal distribution showed an increase in abundance in spring and summer, with the highest aggregations (> 2600 ind·100 m -3 ) of Aglaura hemistoma, Solmundella bitentaculata, Muggiaea atlantica and Pleurobrachia bachei in October and Obelia spp. in February. The highest densities were observed in the coastal station and in the oceanic front, while the oceanic station was characterized by a strong decrease in abundance. The vertical distribution showed that the most dominant species were founded in the first 100 m of the water column, with a higher concentration of organisms in the first 25 or 50 m of depth. This vertical distribution could be limited by presence of a minimum dissolved oxygen layer (< 1 ml·L -1 ) in shallow waters (30-50

Laboratory experiments have determined the behavioral and gross physiological responses ofhydromedusae and ctenophores subjected to sudden changes of salinities in the range that might be encountered in nature. Nine species of hydromedusae (Aequorea victoria, Aglantha digita!e, Bougainviila principis, Gonionemus vertens, Phia!idium gregarium, Polyorchis penicillatus, Proboscidactylaflavicirrata, Sarsia tubulosa, Stomotoca atra) and two species of ctenophores (Boilnopsis infundibulum, Pleurobrachia bache,) were transferred from natural sea water of 3O.5%o to modified sea waters of l9—38%o. Most species altered their density within a few hours by osmoconforming to salinities ranging from 23-38%o, so that equilibrium buoyancy (either positive, neutral, or negative, according to species) was regained along with normal behavior. Even salinity differences of only l-2%o required 30-60 minutes adjustment time. Prior to regaining their equilibrium buoyancies, differences in relative density caused medusae and ctenophores to sink when introduced to low salinity water and to float in high salinity water. Hence, simple density differences combined with the natural intermittent swimming behavior of hydromedusae suggest that in many cases medusae may not actually be able to cross sudden density gradients. In the event that a medusa or ctenophore is moved into water of a different salinity, however, its ability to adjust will allow the animal to resume normal swimming and feeding activities within a short time.

The daily ration and predation impact of medusae and ctenophores in the upper 25 m of Saanich Inlet were determined using data from gut contents analyses, digestion times, and predator/prey densities. The weight-specific daily rations of the 3 major gelatinous predators (Pleurobrachia bachei, Phialidium gregarium, and Phialidium lomae) were a negative power function of their biomass. Small predators obtained a ration much in excess of maintenance needs, while the largest specimens had little excess carbon growth or reproduction. In the upper 25 m predation impact was small on the total mesozooplankton, (mostly

Controlled experiments were conducted by offering eggs, pre-setal trochophores, and setose trochophores of the polychaete Sabellaria cementarium to four planktonic predators, Pleurobrachia bachei (Ctenophora), Aequorea victoria (Hydrozoa), brach-yuran megalopa (Crustacea), and juvenile Sebastes spp. (Pisces). Each predator species captures prey with different mechanisms and the prey, while similar in size, differ in motility and presence or absence of setae.Consumption of non-motile eggs was greater by megalopa but less by A. victoria than consumption of pre-setal trochophores; it is suggested that differences in predator feeding mechanisms account for these differences. Setose trochophores were always consumed at lower rates than the younger stages. The evidence suggests that setae can function in larval defense against an array of predators with different feeding mechanisms, but that swimming may increase, decrease, or have no effect upon rate of predation, depending upon predator species.

Ctenophores and other gelatinous predators in the ocean are ephemeral in their spatial and temporal distributions, but often have a dramatic impact on the dynamics of their prey populations. Considerable information is currently available on the functional and numerical responses of several nearshore ctenophore species; however, an understanding of their potential for shaping the structure of natural zooplankton assemblages requires further information on the selective nature of their predation. Prey selection by the tentaculate ctenophore Pleurobrachia bachei was examined in the laboratory with predation experiments and videotaped observations of predator and prey behavior. Prey types offered to the ctenophore included each of the developmental stages of Calanus pacificus, adult Acartia clausii, and adult Pseudocalanus sp. Pleurobrachia exhibited an unusual, bimodal pattern of prey selection on the different developmental stages of Calanus. Calanus' vulnerability increased through the naupliar stages, dropped at the first copepodid stage, and then rose again throughout the subsequent copepodid stages prior to another decline at the adult stage. Adult Acartia and Pseudocalanus were found to be among the most vulnerable of the prey types offered to Pleurobrachia. We conclude that Pleurobrachia's diet is determined by the relative availability and vulnerability of prey, and that vulnerability to the ctenophore can be predicted from prey swimming speeds and the susceptibility of prey after encounter.

Thirty-three species of gelatinous predators (medusae and ctenophores) were collected in the uppermost 25 m of Saanich Inlet over 3 spring seasons. Of these, 6 species (5 hydromedusae: Aequorea victoria, Aglantha digitale, Mitrocoma cellularia, Phialidium gregarium, and Phialidium lomae; and 1 ctenophore: Pleurobrachia bachei) cornpnsed more than 90 O/O of the total gelatinous predator biomass. P. bachei comprised 40 % of the total dry weight of gelatinous predators, with peak standlng stocks reaching 100 mg DW m-3 (-5 mg C m-3). Phialidium spp, formed 20 % of the total dry weight, with P. gregarium reaching a maxlmum value at 1 station of about 200 mg DW m-3 (-20 mg C m-3). Total gelatinous predator bionlass, at a single stabon, reached nearly 400 mg DW m-3 (-30 mg C m-3) in late May. A conservative estimate of net yearly production in the upper 25 m is 6 to 10 mg C m-J. Standing stocks of individual species had doubling times of 5 to 17 d . Food supply (mainly the abundance of euphausiid eggs), coupled with temperature, were probably the pnmary factors regulating growth and production.

Intercellular gap junctions occur between the ciliated cells that make up the comb plates of the ctenophore Pleurobrachia. Similar junctions are found within the ciliated grooves which run from the apical organ to the first plate of each comb row, as well as throughout the endoderm of the meridional canals. Gap junctions were not found in the ectodermal tissue between the comb rows. The distribution of junctions suggests that excitation conduction within the ciliated grooves, comb plates and meridional canal endoderm may be epithelial.

Measurements were made of the rates at which the ctenophores Pleurobrachia bachei and Bolinopsis microptera feed on copepods. The data were used to ascertain selectivity and rates of procurement of food in the natural habitat. Both ctenophores selected smaller prey (Pseudocalanus minutus) over larger prey (Ephilabidocera amphitrites). P. bachei selected, whereas B. microptera did not appear to select older over younger stages of development of P. minutus. B. microptera fed on smaller prey at a greater rate than did P. bachei. See full-text article at JSTOR