Ctenophores Research Articles

Resolving tricky nodes in the tree of life through amino acid recoding.

Genomic data allowed a detailed resolution of the Tree of Life, but "tricky nodes" such as the root of the animals remain unresolved. Genome-scale datasets are heterogeneous as genes and species are exposed to different pressures, and this can negatively impacts phylogenetic accuracy. We use simulated genomic-scale datasets and show that recoding amino acid data improves accuracy when the model does not account for the compositional heterogeneity of the amino acid alignment. We apply our findings to three datasets addressing the root of the animal tree, where the debate centers on whether sponges (Porifera) or comb jellies (Ctenophora) represent the sister of all other animals. We show that results from empirical data follow predictions from simulations and suggest that, at the least in phylogenies inferred from amino acid sequences, a placement of the ctenophores as sister to all the other animals is best explained as a tree reconstruction artifact.

Two distinct compartments of a ctenophore comb plate provide structural and functional integrity for the motility of giant multicilia

Comb plates are large ciliary structures uniquely seen in comb jellies (ctenophores).1,2,3 A comb plate is constructed from tens of thousands of cilia that are bundled together by structures called compartmenting lamellae (CLs).4,5,6 We previously reported the first component of the CL, CTENO64, and found that it was specifically found in ctenophores and was essential for the determination of ciliary orientation.3 However, CTENO64 is localized only in the proximal region of the CL; therefore, the molecular architecture of the CL over the entire length of a comb plate has not been elucidated. Here, we identified a second CL component, CTENO189. This ctenophore-specific protein was present in the distal region of comb plates, with a localization clearly segregated from CTENO64. Knockdown of the CTENO189 gene using morpholino antisense oligonucleotides resulted in complete loss of CLs in the distal region of comb plates but did not affect the formation of comb plates or the orientation of each cilium. However, the hexagonal distribution of cilia was disarranged, and the metachronal coordination of comb plates along a comb row was lost in the CTENO189 morphants. The morphant comb plate showed asymmetric ciliary-type movement in normal seawater, and in a high-viscosity solution, it could not maintain the normal waveforms but showed a symmetric flagellar-type movement. Our findings demonstrated two distinct compartments of a comb plate: the proximal CL as the building foundation that rigidly fixes the ciliary orientation, and the distal CL that reinforces the elastic connection among cilia to overcome the hydrodynamic drag of giant multiciliary plates.

Speciation of pelagic zooplankton: Invisible boundaries can drive isolation of oceanic ctenophores.

The study of evolution and speciation in non-model systems provides us with an opportunity to expand our understanding of biodiversity in nature. Connectivity studies generally focus on species with obvious boundaries to gene flow, but in open-ocean environments, such boundaries are difficult to identify. Due to the lack of obvious boundaries, speciation and population subdivision in the pelagic environment remain largely unexplained. Comb jellies (Phylum Ctenophora) are mostly planktonic gelatinous invertebrates, many of which are considered to have freely interbreeding distributions worldwide. It is thought that the lobate ctenophore Bolinopsis infundibulum is distributed throughout cooler northern latitudes and B. vitrea warmer. Here, we examined the global population structure for species of Bolinopsis with genetic and morphological data. We found distinct evolutionary patterns within the genus, where B. infundibulum had a broad distribution from northern Pacific to Atlantic waters despite many physical barriers, while other species were geographically segregated despite few barriers. Divergent patterns of speciation within the genus suggest that oceanic currents, sea-level, and geological changes over time can act as either barriers or aids to dispersal in the pelagic environment. Further, we used population genomic data to examine evolution in the open ocean of a distinct lineage of Bolinopsis ctenophores from the North Eastern Pacific. Genetic information and morphological observations validated this as a separate species, Bolinopsis microptera, which was previously described but has recently been called B. infundibulum. We found that populations of B. microptera from California were in cytonuclear discordance, which indicates a secondary contact zone for previously isolated populations. Discordance at this scale is rare, especially in a continuous setting.

Ctenophores and the evolutionary origin(s) of neurons

Ctenophores (commonly known as comb jellies) are among the earliest branching extant lineages of the animal kingdom. Here, I present a brief overview of the ctenophore nervous system, discussing its cellular architecture and molecular composition, as well as insights it offers into the early evolution of neurons and chemical neurotransmission.

Feral Atlas: The More-Than-Human Anthropocene ed. by Anna L. Tsing et al.

Reviewed by: Feral Atlas: The More-Than-Human Anthropocene ed. by Anna L. Tsing et al. Elexis Trinity Williams Tsing, Anna L., Jennifer Deger, Alder Keleman Saxena, and Feifei Zhou, eds. Feral Atlas: The More-Than-Human Anthropocene. Redwood City, CA: Stanford University Press, 2021. Playful disorientation is perhaps your first hint: this is not scholarship as usual. A white page opens on the cluttered desktop landscape of the computer screen, populated by colorful illustrations of fire, kudzu, and an emerald ash borer. One is compelled by the visual sensuality of the experience to sit with it for a moment, to "stay with the trouble," as Donna Haraway (2016) might say, of exploring the patchy problematics of the Anthropocene. Attending to the materiality of land, water, and atmosphere-transforming projects, this transdisciplinary anthology centers four historical concurrences at the intersection of human and nonhuman activity, described as "Anthropocene Detonators": invasion, empire, capital, and acceleration. Here there be monsters, certainly, but perhaps also opportunities for responsiveness and responsibility. One encounters, mingling on the landing page, a host of feral entities in motion: toxic fog, antibiotics, comb jellies, anti-fouling paint, bee villains. Each is associated with one of the four detonators that structure the project. These focal points are accompanied by one of 79 field reports representing a window into a different multispecies ecology that proliferates in the intermingling trails of human infrastructures and nonhuman entities. In the upper left-hand corner, an illustrated master key directs the reader to an index of related cases and concepts. It is a feature which contributes to the sense in which the project registers as an atlas, further articulating its virtual spatiality by introducing a reading room in which texts and other [End Page 719] media are organized by type and conceptual analytic. Among these analytic frames, one finds Tippers—described as "modes of infrastructure-mediated state change"1—and Feral Qualities, which identify ecologies and entities that flourish in the context of human disturbance, proliferating in toxic environments or stowing away in industrial infrastructures. Such qualities are identified by their compatibility and potential for imagining otherwise, with rather than against the realities of the Anthropocene. Click on the mobile icon of dry, cracking ground titled "ghost water," for example, and you will be drawn deeper into iterations of the linked concepts of smoothness and speed in relationship to empire. These elements of change are used to structure explorations of the myriad processes by which the "smooth surfaces of land and water have enabled colonial governance and industrial development [sponsoring]…more than human invasions" and accelerating processes which open "portals for feral effects, and [block] the healing of local ecologies by denying them time" for more subtle adaptations.2 Drawing together transport infrastructure, water, and state power within the framework of the non-innocent but potential-bearing effects of technoscientific acceleration in this one strand, the reader moves beyond the analytic limitations of the "entity" itself toward a layered, polyphonic inquiry of the relations which occur among human projects, living, and nonliving beings. This, we are to understand as a function of reading the dynamic intersection of smoothness and speed as a Tipper. Grounded in a particular time and place, each of the Tippers represents analytic meditations on the relational processes by which infrastructural efforts shape change. Like the choose-your-own-adventure novels of the 1980s, Feral Atlas teases its possibilities and structures its interactive experience so that you may play with its pieces however you choose, but the concepts are all embedded in rich relations of multispecies complexity and transformation. As both readers and players in this visual entanglement, we are invited to explore what it means to map, interpret, or intervene in the ruination and the promise of the Anthropocene—its infrastructural effects and the opportunities for imagining otherwise that lay deep in the weeds (or the semi-wilds) where human tracks are everywhere evident but do not dominate the landscape of the possible. Beyond its layered interface and the hypertextual user experience, one finds in Feral Atlas something of a guide to the places, processes, and interactions by which feral ecologies spring up. It is an accessible tool for disciplining...

Studying Ctenophora WBR Using Mnemiopsis leidyi.

Ctenophores, also known as comb jellies, are a clade of fragile holopelagic, carnivorous marine invertebrates, that represent one of the most ancient extant groups of multicellular animals. Ctenophores show a remarkable ability to regenerate in the adult form, being capable of replacing all body parts (i.e., whole-body regeneration) after loss/amputation. With many favorable experimental features (optical clarity, stereotyped cell lineage, multiple cell types), a full genome sequence available and their early branching phylogenetic position, ctenophores are well placed to provide information about the evolution of regenerative ability throughout the Metazoa. Here, we provide a collection of detailed protocols for use of the lobate ctenophore Mnemiopsis leidyi to study whole-body regeneration, including specimen collection, husbandry, surgical manipulation, and imaging techniques.

Black Sea Mnemiopsis leidyi (Ctenophora) adult locomotion and light-induced behavior in laboratory experiments

The capacity of Ctenophores to sense light is indicated by comparative morphology and genomics data, but the relevant behavioral responses of the animals to light stimulus have not been studied yet. We developed the design of a laboratory experiment to reveal the light-induced behavior of adult Mnemiopsis leidyi from the Black Sea and identified criteria for its evaluation. Average swimming speed up to ~6–7 mm s−1 can be considered specific for the M. leidyi adults under rest or active feeding. Ctenophore reacts to a sharp light rise as an external stimulus, briefly increasing the rate several times (up to 40 mm sec−1). Analysis of motion vectors revealed no directional movement from the light source or towards it. Maximum and average rates decrease significantly for two minutes after the light is turned on, and speeds return to the original values within an hour. Small animals are more active than large ones. The mean motion rates of small comb jellies (<60 mm) were 0.7 ± 0.84 mm s−1 and 0.18 ± 0.19 mm s−1 - for large animals (>80 mm) when averaging the data for the entire observation period (from February to June).

Depth- and temperature-specific fatty acid adaptations in ctenophores from extreme habitats.

ABSTRACTAnimals are known to regulate the composition of their cell membranes to maintain key biophysical properties in response to changes in temperature. For deep-sea marine organisms, high hydrostatic pressure represents an additional, yet much more poorly understood, perturbant of cell membrane structure. Previous studies in fish and marine microbes have reported correlations with temperature and depth of membrane-fluidizing lipid components, such as polyunsaturated fatty acids. Because little has been done to isolate the separate effects of temperature and pressure on the lipid pool, it is still not understood whether these two environmental factors elicit independent or overlapping biochemical adaptive responses. Here, we use the taxonomic and habitat diversity of the phylum Ctenophora to test whether distinct low-temperature and high-pressure signatures can be detected in fatty acid profiles. We measured the fatty acid composition of 105 individual ctenophores, representing 21 species, from deep and shallow Arctic, temperate, and tropical sampling locales (sea surface temperature, −2° to 28°C). In tropical and temperate regions, remotely operated submersibles (ROVs) enabled sampling down to 4000 m. We found that among specimens with body temperatures 7.5°C or colder, depth predicted fatty acid unsaturation levels. In contrast, in the upper 200 m of the water column, temperature predicted fatty acid chain lengths. Taken together, our findings suggest that lipid metabolism may be specialized with respect to multiple physical variables in diverse marine environments. Largely distinct modes of adaptation to depth and cold imply that polar marine invertebrates may not find a ready refugium from climate change in the deep.

Ecological state of marine pelagic communities near the Verbyanaya spit (Temryuk Gulf, Azov Sea)

Phytoplankton, ciliates, holoplankton, meroplankton, ichthyoplankton, ctenophores were studied in the vicinity of the Verbyanaya spit in the Temryuk Gulf during the month of June, which is the most productive month. It has been discovered that formation of net zooplankton structure was largely determined by predator-prey trophic relations. Leanness of ichthyoplankton and mosaic distribution of holoplanktron and meroplankton is evidently explained by the abundance of large carnivorous comb jellies Mnemiopsis leidyi.. Dominant holoplankton complex was represented with marine euryhaline species of copepods – Acartia tonsa (93–98% of the total holoplankton amount). Larvae of Mytilaster lineatus bivalves, comprised a significant part of net zooplankton (43.5%). A total biomass of zooplankton on average reached 537.4 mg/m3, at that, ciliates comprised 38% of this amount. Abundance of zooplankton in the area of research is largely explained by a high level of trophicity of waters coming with the flow of the Kuban River. The obtained results offer an insight into ecological state of marine pelagic communities in protected zones of eastern Azov region and may be useful for subsequent monitoring of the region.

A late-surviving stem-ctenophore from the Late Devonian of Miguasha (Canada)

Like other soft-bodied organisms, ctenophores (comb jellies) produce fossils only under exceptional taphonomic conditions. Here, we present the first record of a Late Devonian ctenophore from the Escuminac Formation from Miguasha in eastern Canada. Based on the 18-fold symmetry of this disc-shaped fossil, we assign it to the total-group Ctenophora. Our phylogenetic analyses suggest that the new taxon Daihuoides jakobvintheri gen. et sp. nov. falls near Cambrian stem ctenophores such as ‘dinomischids’ and 'scleroctenophorans'. Accordingly, Daihuoides is a Lazarus-taxon, which post-dates its older relatives by over 140 million years, and overlaps temporally with modern ctenophores, whose oldest representatives are known from the Early Devonian. Our analyses also indicate that the fossil record of ctenophores does not provide strong evidence for or against the phylogenomic hypothesis that ctenophores are sister to all other metazoans.

Revision of Beroidae (Ctenophora) in the southern seas of Europe: systematics and distribution based on genetics and morphology

AbstractGenetic and morphological analyses were used to revise historical controversies in identities of Beroe species in the southern seas of Europe. DNA analyses with ITS sequences were used to explore their phylogenetic relationships. Three species of Beroe were initially listed as occurring in the Mediterranean Sea. Recently, the specimens were often re-identified using genetic analyses, causing confusions of identity. In 1997, a non-native Beroe was introduced into the Black Sea, which established there and spread to the adjacent seas, adding more controversy and confusion to species identification in this group of comb jellies.Our revisions suggest the following systematic changes: (1) re-naming of the species from what was initially labelled as Beroe ovata, and later as B. cucumis (sensuMayer, 1912), to Beroe pseudocucumis sp. nov.. (2) Beroe mitrata but not Beroe ‘anatoliensis’ inhabits the Aegean Sea, as was reported previously. (3) Beroe ovata is the only species of Beroidae that became invasive and should be used with the authority of Bruguière, 1789, but not in the sense of Mayer, 1912. (4) Beroe forskalii appears to be represented by two species in the Mediterranean and in the Antarctic, but further justification is needed. (5) Beroe cucumis is a species of bipolar occurrence, inhabiting both subpolar areas and its recent definition as Beroe ‘norvegica’ is incorrect.

Cambrian comb jellies from Utah illuminate the early evolution of nervous and sensory systems in ctenophores

SummaryCtenophores are a group of predatory macroinvertebrates whose controversial phylogenetic position has prompted several competing hypotheses regarding the evolution of animal organ systems. Although ctenophores date back at least to the Cambrian, they have a poor fossil record due to their gelatinous bodies. Here, we describe two ctenophore species from the Cambrian of Utah, which illuminate the early evolution of nervous and sensory features in the phylum. Thalassostaphylos elegans has 16 comb rows, an oral skirt, and an apical organ with polar fields. Ctenorhabdotus campanelliformis has 24 comb rows, an oral skirt, an apical organ enclosed by a capsule and neurological tissues preserved as carbonaceous films. These are concentrated around the apical organ and ciliated furrows, which connect to a circumoral nerve ring via longitudinal axons. C. campanelliformis deviates from the neuroanatomy of living ctenophores and demonstrates a substantial complexity in the nervous system of Cambrian ctenophores.

Opechona chloroscombri and Opechona corkumi n. sp. (Digenea: Lepocreadiidae) from the Northern Gulf of Mexico with Phylogenetic Analysis Based on 28S RDNA

This study investigated the identity of 2 lepocreadiid digenean species belonging in the genus Opechona Looss, 1907 that infect littoral fishes of the northern Gulf of Mexico. Opechona chloroscombriNahhas and Cable, 1964, a species previously known only from the Caribbean Sea and the Atlantic Ocean off Brazil, is reported herein from the Atlantic bumper, Chloroscombrus chrysurus (L.), in the northern Gulf of Mexico. A second species infects the gulf butterfish, Peprilus burti Fowler, and the American harvestfish, Peprilus paru (L.), and it is described as a new species that occurs in coastal waters of the north-central and northeastern Gulf of Mexico. Metacercariae infecting the mesoglea of pelagic jellyfishes (Bougainvillia carolinensis [McCady], Chrysaora quinquecirrha [Desor], and Stomolophus meleagris Agassiz) and pelagic comb jellies (Mnemiopsis leidyi Agassiz and Beroe ovata Bruguière) were collected that resemble the new species but require further study to identify. Newly generated sequence fragments (28S rDNA) from both species of Opechona plus 2 other lepocreadiids collected during the study were aligned with publicly available sequences from 18 other lepocreadiids, 6 species of Aephnidiogenidae Yamaguti, 1934, and 2 species of Gorgocephalidae Manter, 1966. The alignment was subjected to Bayesian inference analysis rooted using a gorgocephalid. The resulting tree estimated the positions of both Opechona spp. as being unresolved within a group of taxa that included all available species of Opechona plus available species from the morphologically similar genera ProdistomumLinton, 1910, Preptetos Pritchard, 1960, and Clavogalea Bray, 1985. Although relatively similar in morphology, the 2 studied species of Opechona were surprisingly not closely related. Opechona cablei (Stunkard, 1980) Bray and Gibson, 1990 is herein considered to be a junior synonym of Opechona pyriformis (Linton, 1900) Bray and Gibson, 1990.

Hidden diversity of Ctenophora revealed by new mitochondrial COI primers and sequences.

The mitochondrial gene cytochrome‐c‐oxidase subunit 1 (COI) is useful in many taxa for phylogenetics, population genetics, metabarcoding, and rapid species identifications. However, the phylum Ctenophora (comb jellies) has historically been difficult to study due to divergent mitochondrial sequences and the corresponding inability to amplify COI with degenerate and standard COI “barcoding” primers. As a result, there are very few COI sequences available for ctenophores, despite over 200 described species in the phylum. Here, we designed new primers and amplified the COI fragment from members of all major groups of ctenophores, including many undescribed species. Phylogenetic analyses of the resulting COI sequences revealed high diversity within many groups that was not evident from more conserved 18S rDNA sequences, in particular among the Lobata (Ctenophora; Tentaculata; Lobata). The COI phylogenetic results also revealed unexpected community structure within the genus Bolinopsis, suggested new species within the genus Bathocyroe, and supported the ecological and morphological differences of some species such as Lampocteis cruentiventer and similar undescribed lobates (Lampocteis sp. “V” stratified by depth, and “A” differentiated by colour). The newly designed primers reported herein provide important tools to enable researchers to illuminate the diversity of ctenophores worldwide via quick molecular identifications, improve the ability to analyse environmental DNA by improving reference libraries and amplifications, and enable a new breadth of population genetic studies.

Rooting the Animal Tree of Life.

Identifying our most distant animal relatives has emerged as one of the most challenging problems in phylogenetics. This debate has major implications for our understanding of the origin of multicellular animals and of the earliest events in animal evolution, including the origin of the nervous system. Some analyses identify sponges as our most distant animal relatives (Porifera-sister hypothesis), and others identify comb jellies (Ctenophora-sister hypothesis). These analyses vary in many respects, making it difficult to interpret previous tests of these hypotheses. To gain insight into why different studies yield different results, an important next step in the ongoing debate, we systematically test these hypotheses by synthesizing 15 previous phylogenomic studies and performing new standardized analyses under consistent conditions with additional models. We find that Ctenophora-sister is recovered across the full range of examined conditions, and Porifera-sister is recovered in some analyses under narrow conditions when most outgroups are excluded and site-heterogeneous CAT models are used. We additionally find that the number of categories in site-heterogeneous models is sufficient to explain the Porifera-sister results. Furthermore, our cross-validation analyses show CAT models that recover Porifera-sister have hundreds of additional categories and fail to fit significantly better than site-heterogenuous models with far fewer categories. Systematic and standardized testing of diverse phylogenetic models suggests that we should be skeptical of Porifera-sister results both because they are recovered under such narrow conditions and because the models in these conditions fit the data no better than other models that recover Ctenophora-sister.

Whole-Body Regeneration in the Lobate Ctenophore Mnemiopsis leidyi.

Ctenophores (a.k.a. comb jellies) are one of the earliest branching extant metazoan phyla. Adult regenerative ability varies greatly within the group, with platyctenes undergoing both sexual and asexual reproduction by fission while others in the genus Beroe having completely lost the ability to replace missing body parts. We focus on the unique regenerative aspects of the lobate ctenophore, Mnemiopsis leidyi, which has become a popular model for its rapid wound healing and tissue replacement, optical clarity, and sequenced genome. M. leidyi’s highly mosaic, stereotyped development has been leveraged to reveal the polar coordinate system that directs whole-body regeneration as well as lineage restriction of replacement cells in various regenerating organs. Several cell signaling pathways known to function in regeneration in other animals are absent from the ctenophore’s genome. Further research will either reveal ancient principles of the regenerative process common to all animals or reveal novel solutions to the stability of cell fates and whole-body regeneration.

Winter-Spring Development of the Zooplankton Community Below Sea Ice in the Arctic Ocean

The impact of the rapidly changing Arctic on zooplankton community structure and seasonal behaviour is not yet understood. Here we examine 6 months of under-ice zooplankton observations from the N-ICE2015 expedition (January to June 2015) in the Nansen Basin and on the Yermak Plateau north of Svalbard. Stratified sampling in the water column was done with MultiNet during the entire expedition, and sampling in the upper 5 m below sea ice was performed during April-May by divers using a hand-held net. Hydrographic conditions were dominated by northward-flowing warm and saline Atlantic Water at intermediate depth, and southward-flowing cold Polar Surface Water in the upper 100 m. The mesozooplankton was dominated by copepods. Most numerous were the small ubiquitousOithona similisin the upper 200 m, withMicrocalanusspp. andTriconia borealisfurther down the water column.Calanus finmarchicusdominated among theCalanusspecies whileMetridia longawas also numerous. The most abundant deep-water copepods wereParaeuchaetaspp. andSpinocalanusspp. Arrow worms (Chaetognatha) and comb jellies (Ctenophora) were the most numerous non-copepods. The mesozooplankton community was more dependent on surrounding water mass characteristics, such as salinity and depth, than geographical location. Algal food availability, which was closely linked to seasonality, explained the community changes seen in surface waters in May and June due to seasonal ascent and recruitment. Seasonal changes from winter to spring mostly involved an increase in the herbivorousC. finmarchicusand its nauplii in the upper 200 m of the water column coinciding with the peak of the phytoplankton bloom in late May. The Yermak Plateau and adjacent Nansen Basin were characterised by oceanic North Atlantic and Arctic species, many of which are deep water specialists. Despite the late onset of the spring bloom due to consolidated sea ice, both North Atlantic and Arctic species successfully reproduced in the study area. This explains the species-rich mesozooplankton community in this region as opposed to the less productive central Arctic Ocean. Future prospects of less sea ice and earlier onset of the bloom will likely be positive for the overall secondary production by both Arctic and boreal zooplankton in this region.

Evidence for sponges as sister to all other animals from partitioned phylogenomics with mixture models and recoding

Resolving the relationships between the major lineages in the animal tree of life is necessary to understand the origin and evolution of key animal traits. Sponges, characterized by their simple body plan, were traditionally considered the sister group of all other animal lineages, implying a gradual increase in animal complexity from unicellularity to complex multicellularity. However, the availability of genomic data has sparked tremendous controversy as some phylogenomic studies support comb jellies taking this position, requiring secondary loss or independent origins of complex traits. Here we show that incorporating site-heterogeneous mixture models and recoding into partitioned phylogenomics alleviates systematic errors that hamper commonly-applied phylogenetic models. Testing on real datasets, we show a great improvement in model-fit that attenuates branching artefacts induced by systematic error. We reanalyse key datasets and show that partitioned phylogenomics does not support comb jellies as sister to other animals at either the supermatrix or partition-specific level.

Diversity and Physiological Tolerance of Native and Invasive Jellyfish/Ctenophores along the Extreme Salinity Gradient of the Baltic Sea

Global change has led to manifold changes of marine ecosystems and biodiversity world-wide. While it has been shown that certain jellyfish and comb jelly species have increased regionally, it remains to be investigated if this is a general trend or localized phenomenon. Especially for the economically important Baltic Sea, which is characterized by an extreme physical environmental gradient, this question has not been addressed to date. Here we present a detailed account of the gelatinous macro-zooplankton community including their physiological tolerance towards abiotic conditions and resulting distribution ranges in the Baltic. We show that the arrival and establishment of non-indigenous species has led to a rising importance of jellyfish and comb jellies in the Baltic. This accounts for the comb jelly Mnemiopsis leidyi, which was first observed in Northern Europe in 2005, as well as for the hydromedusae Blackfordia virginica, first sighted in 2014. Both species have been shown to attain high population densities with pronounced grazing impact in other invasive regions. Given the current and anticipated changes of the physical environment of the Baltic Sea, especially ongoing warming, amplification of their impact can be expected.

A sticky thicket of glue cells: A comparative morphometric analysis of colloblasts in 20 species of comb jelly (phylum Ctenophora)

Ctenophores in the class Tentaculata are distinct from Cnidarians in that they use sticky, not stinging, tentacles to capture and subdue their prey. The structures that make these tentacles sticky are colloblasts, specialized multicellular adhesive structures for predation. Located on the tentacles, tentacle side-branches (tentilla), or oral tentilla, colloblasts are only found in comb jellies (phylum Ctenophora). To perform comparative anatomy of the diversity of ctenophore colloblasts, specimens were collected from the epi- to bathypelagic zones near the coasts of central California and the Hawaiian Islands using blue-water divers and remotely operated vehicles. Tentacle samples were immediately fixed in a 4% formalin solution at sea, and then prepared in the lab via secondary fixation in 2% OsO4 for scanning electron microscopy (SEM). Diversity of ultrastructural characteristics was observed using SEM, and the morphometrics of the collosphere, external secretion granules, and spiral filament were recorded for 20 species, within 9 families and 9 genera, including 13 undescribed species. Morphometry of colloblasts reveals that the shape of the collosphere (the organizational unit of sticky granules) falls into 3 classifications: spherical, ellipsoidal, or non-uniform. External secretion granule deposition falls into 2 categories: clustered or patterned; the cap cell membrane was either present or absent. This morphological variation is summarized graphically and will be useful to describe the functional diversity and feeding ecology of the interesting and controversial phylum Ctenophora.