Chaetognaths Research Articles

Little seasonal variation of mercury concentrations and biomagnification in an Arctic pelagic food web

Despite numerous studies on mercury in Arctic biota, data from inaccessible, ice-covered regions − especially during the polar night and late winter − remain scarce. This scarcity results in poor understanding of the seasonal dynamics of mercury within the food web. From the Northern Barents Sea, we quantified total mercury and the dietary descriptors δ15N and δ13C as long-term dietary signals (weeks to months) in biota to a) investigate the seasonal pelagic food web structure, b) seasonality in total mercury concentration, c) and its biomagnification in the food web. Mercury and dietary descriptors were analyzed in copepods, macrozooplankton (krill, amphipods, arrow worms and pteropods) and the fishes, Atlantic cod (Gadus morhua), polar cod (Boreogadus saida) and capelin (Mallotus villosus) during spring, late summer, early,and late winter. Seasonal changes were observed in δ15N values in some macrozooplankton and capelin, and some seasonal variation was observed across the food web with depleted δ13C values in spring and enriched δ13C values in late summer. Mercury concentrations were lower (range: 2.49 ng/g dw in the krill Thyssanossa sp. – 70.55 ng/g dw in the pelagic pteropod Clione limacina) than reported from other parts of the Arctic. We found a positive linear relationship between mercury and relative trophic position represented by δ15N, i.e., biomagnification, during all seasons, except in early winter. As Clione limacina likely had different turnover rates for mercury and stable isotopes resulting in low δ15N, but high mercury concentrations in early winter, compared to the other species in the food web, the pteropod was omitted from the regression. By omitting Clione limacina, biomagnification was similar across all seasons (R2adj = 0.45). Thus, we saw clear mercury biomagnification with consistent and little seasonal variation in this high Arctic marine food web despite large seasonal fluctuations in abiotic and biotic conditions.

Characterization of eyes, photoreceptors, and opsins in developmental stages of the arrow worm Spadella cephaloptera (Chaetognatha).

The phylogenetic position of chaetognaths, or arrow worms, has been debated for decades, however recently they have been grouped into the Gnathifera, a sister clade to all other Spiralia. Chaetognath photoreceptor cells are anatomically unique by exhibiting a highly modified cilium and are arranged differently in the eyes of the various species. Studies investigating eye development and underlying gene regulatory networks are so far missing. To gain insights into the development and the molecular toolkit of chaetognath photoreceptors and eyes a new transcriptome of the epibenthic species Spadella cephaloptera was searched for opsins. Our screen revealed two copies of xenopsin and a single copy of peropsin. Gene expression analyses demonstrated that only xenopsin1 is expressed in photoreceptor cells of the developing lateral eyes. Adults likewise exhibit two xenopsin1 + photoreceptor cells in each of their lateral eyes. Beyond that, a single cryptochrome gene was uncovered and found to be expressed in photoreceptor cells of the lateral developing eye. In addition, cryptochrome is also expressed in the cerebral ganglia in a region in which also peropsin expression was observed. This condition is reminiscent of a nonvisual photoreceptive zone in the apical nervous system of the annelid Platynereis dumerilii that performs circadian entrainment and melatonin release. Cryptochrome is also expressed in cells of the corona ciliata, an organ in the posterior dorsal head region, indicating a role in circadian entrainment. Our study highlights the importance of the Gnathifera for unraveling the evolution of photoreceptors and eyes in Spiralia and Bilateria.

Non-target and suspect screening reveal complex pattern of contamination in Arctic marine zooplankton

Although increasing, there is still limited knowledge of the presence of ‘contaminants of emerging concern’ in Arctic marine biota, particularly in lower trophic species. In the present study, we have applied a novel pipeline to investigate the presence of contaminants in a variety of benthic and pelagic low-trophic organisms: amphipods, copepods, arrow worms and krill. Samples collected in Kongsfjorden in Svalbard in 2018 were subject to extraction and two-dimensional gas chromatography coupled to high-resolution mass spectrometry (GC×GC-HRMS). Tentatively identified compounds included plastic additives, antioxidants, antimicrobials, flame retardants, precursors, production solvents and chemicals, insecticides, and pharmaceuticals. Both legacy contaminants (PAHs, PCBs, PBDEs, hexachlorobenzene) as well as novel and emerging contaminants (triclosan, bisphenol A, and ibuprofen) were quantified in several species using target analysis by GC–MS/MS. The significance of these discoveries is discussed considering the potential for detrimental effects caused by these chemicals, as well as suggested local and distant sources of the components to the Arctic environment.

Diversity and distribution of arrow worms, zooplankton along the Mangaluru and Udupi Coast, Karnataka

Diversity and distribution of arrow worms, zooplankton along the Mangaluru and Udupi Coast, Karnataka

Boat paint and epoxy fragments - Leading contributors of microplastic pollution in surface waters of a protected Andaman bay

Plastic pollution is a growing concern even in India's remotest oceanic islands. To understand the extent of the problem in relatively undisturbed areas of the Andaman and Nicobar Islands, we nested a microplastic survey within a year-long meroplankton study in the protected bay of the Lohabarrack salt water crocodile sanctuary, that lies on the less populated west coast of South Andaman Island. Surveys recovered microplastics year-round, in 299 out of 300 samples. The average microplastic density in the protected bay was 0.45 ± 0.32 particles per m3. Densities were highest during the monsoon, peaking at 2.34 particles per m3. Marine coating fragments (boat paint and epoxy, 58%) dominated the plastic debris composition year-round, while fibre only amounted to 15%. Marine coating fragments were most frequently encountered during the pre-monsoon, while fibres and other miscellaneous debris grew in abundance during the monsoon and post-monsoon months. Marine coating fragments were eaten by arrow worms, gastropods, appendicularians and Lucifer shrimp, and constituted 7% of the arrow worm diet. Microplastic density and composition found in this west facing protected bay was in stark contrast to the previously published observations from the east facing, human dominated Port Blair bay, providing clear indication of sources and potential mitigation strategies. This is the first year-long record of ocean plastics from the Andaman Islands, India and it provides evidence of pollution by boat paint and epoxy particles, an often-overlooked component of microplastic pollution.

Towards Automated Classification of Zooplankton Using Combination of Laser Spectral Techniques and Advanced Chemometrics.

Zooplankton identification has been the subject of many studies. They are mainly based on the analysis of photographs (computer vision). However, spectroscopic techniques can be a good alternative due to the valuable additional information that they provide. We tested the performance of several chemometric techniques (principal component analysis (PCA), non-negative matrix factorisation (NMF), and common dimensions and specific weights analysis (CCSWA of ComDim)) for the unsupervised classification of zooplankton species based on their spectra. The spectra were obtained using laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy. It was convenient to assess the discriminative power in terms of silhouette metrics (Sil). The LIBS data were substantially more useful for the task than the Raman spectra, although the best results were achieved for the combined LIBS + Raman dataset (best Sil = 0.67). Although NMF (Sil = 0.63) and ComDim (Sil = 0.39) gave interesting information in the loadings, PCA was generally enough for the discrimination based on the score graphs. The distinguishing between Calanoida and Euphausiacea crustaceans and Limacina helicina sea snails has proved possible, probably because of their different mineral compositions. Conversely, arrow worms (Parasagitta elegans) usually fell into the same class with Calanoida despite the differences in their Raman spectra.

Taxonomic reassessment of chaetognaths (Chaetognatha, Sagittoidea, Aphragmophora) from Korean waters.

Since the first record of chaetognaths (arrow worms) reported from Korean waters by Molchanov in 1907, three families, 12 genera and 21 species have been additionally described. Eighteen of the 21 recorded species have been reported under scientific names different from the latest taxonomic system. This study aimed to address this issue by conducting a taxonomic re-evaluation of chaetognaths collected from Korean waters. Furthermore, the taxonomic usefulness of morphological differences in corona ciliata and distribution of ciliary sense receptors were re-examined using specimens stained with 1% Chlorazol black E (CBE) solution. This study includes taxonomically-validated voucher specimens of 18 species from Korean waters. Based on the specimens, re-description including image data and CBE staining pattern, distribution, ecological information and improved key were provided for each species. However, Decipisagittadecipiens, Serratosagittaserratodentata and Sagittapseudoserratodentata from Korean waters is still questioned because of the paucity of the voucher specimen and scientific literature.

Effects of Terrestrial Inputs on Mesozooplankton Community Structure in Bohai Bay, China

Zooplankton play a pivotal role in connecting primary producers and high trophic levels, and changes in their temporal and spatial distribution may affect the entire marine ecosystem. The spatial and seasonal taxonomic composition patterns of mesozooplankton in Bohai Bay were investigated in relation to a number of water parameters. Bohai Bay is a eutrophic semi-enclosed bay with dynamic physico-chemical conditions influenced by terrestrial inputs and seawater intrusion. The results showed that under the condition of terrigenous input, the diversity of mesozooplankton species near the eutrophic Haihe River Estuary and Jiyun River Estuary was lower than that in the central Bohai Bay, with gelatinous Oikopleura dioica as the dominant species. The mesozooplankton diversity was highest in the bay mouth affected by seawater intrusion, and the dominant oceanic species, mainly copepods Corycaeus affinis, Calanus sinicus, and Oithona similis, entered the inner bay from the bay mouth. Meanwhile, the abundance of mesozooplankton in summer was significantly higher than that in autumn. Compared with historical data, the dominant species in Bohai Bay has evolved from arrow worm Sagitta crassa to copepod Paracalanus parvus, probably due to global warming, indicating the effects of human activities on the succession of mesozooplankton community.

A novel approach for discovering correlations between elemental and molecular composition using laser-based spectroscopic techniques.

Modern analytical techniques, including laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy, yield multidimensional data, which are most efficiently used in conjunction with chemometric techniques, including multi-block algorithms. In this study, we use several algorithms for the processing of laser-induced breakdown and Raman spectra of zooplankton organisms, which are found to accumulate lithium for an unknown reason. Correlations between elemental and molecular composition of zooplankton have been found. We studied 29 samples: crustaceans, arrow worms, and sea snails. The obtained spectra were examined by principal component analysis (PCA), non-negative matrix factorization (NMF), consensus PCA (CPCA), and analysis of common components and specific weights (CCSWA, or ComDim). LIBS spectra are more sensitive towards taxonometric differences than Raman spectra. All the algorithms gave similar results, although still differing in details. Data fusion revealed a number of relationships, including the correlation of Li with potassium (R = 0.83, n = 14), with Raman bands of carotenoids (R = 0.89, n = 11) and tryptophan (R = 0.94, n = 9). The correlations were most pronounced in light-coloured parts of the inhomogeneous biological material. Ratios of fatty acids are associated with Li concentration if above 200 mg kg-1. Valine is also related to the Li accumulation. Thus, it is shown that the combination of LIBS and Raman spectroscopy, followed by appropriate mathematical treatment, is a convenient tool for comprehensive studies of environmental objects.

The Sizes, Growth and Reproduction of Arrow Worms (Chaetognatha) in Light of the Gill-Oxygen Limitation Theory (GOLT)

The Chaetognatha are a marine invertebrate phylum including 132 extant, carnivorous species in nine families and two orders, but with unclear protostomian affinities in the animal kingdom. We document the gradual recognition of the distinctiveness of chaetognaths by early taxonomists, with some emphasis on the often-overlooked studies by Chinese marine biologists. The carnivorous arrow worms are understudied relative to their importance in the marine zooplankton, where they rank second in abundance after the herbivorous copepods. Although arrow worms lack gills or other dedicated respiratory organs, we show that the Gill-Oxygen Limitation Theory (GOLT) can be used to explain how temperature and respiration affect their growth and related life-history traits. Notably, we present a reappraisal of evidence for size–temperature relationships between and within chaetognath species, and for the relationship between their temperature-mediated oxygen demand and their growth patterns. Von Bertalanffy weight growth curves of Ferosagitta hispida (family: Sagittidae) based on earlier aquarium experiments by various authors are presented, which suggest (a) a good fit and (b) that the life span of chaetognaths is much lower than suggested by the authors of several published growth curves drawn onto length–frequency samples from the wild. In addition, we show that chaetognaths attain first maturity at a fraction of the maximum length they can attain that is similar to the corresponding fraction in fishes. Overall, we suggest that the manner in which the oxygen they require enters the body of small marine invertebrates, although often neglected, is a crucial aspect of their biology. In addition, based on our result that arrow worms conform to the GOLT, we suggest that this theory may provide the theoretical framework for the study of growth in the other water-breathing ectotherms lacking gills.

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.

Evolutionary analyses of phylum Chaetognatha based on mitochondrial cytochrome oxidase I gene

Chaetognaths (arrow worms) are an enigmatic group of transparent planktonic invertebrates and play an important role in the marine food web. Their morphological and developmental features have raised extensive debates since the discovery of the phylum in the 18th century. Uncertainty in the phylogenetic placement of certain chaetognath species still exists and is puzzling many scientists who have tried to clarify this task. Studies using a portion of both small subunit ribosomal ribonucleic acid (SSU rRNA) and large subunit ribosomal ribonucleic acid (LSU rRNA) genes when integrated with conventional taxonomy were contributed to resolve taxonomical issues in this group. Here we present the first phylogenetic study of Chaetognatha based on a portion of mitochondrial cytochrome oxidase I (COI) gene and compare our results with the earlier morphological and molecular evolutionary hypotheses. This study includes 16 extant species, representing 8 genera and 6 of which are among the 9 extant families. We recommend the following clade structure for the phylum: Aphragmophora comprising Sagittidae with Pterosagittidae and Krohnittidae included in the Sagittidae and Phragmophora comprising Eukrohniidae, Spadellidae, and Heterokrohniidae. Phylogenetic analyses also supported the division of Phragmophora into two monophyletic groups: the Monophragmophora and Biphragmophora. Moreover, Ctenodontina/Flabellodontina and Syngonata/Chorismogonata suborders were not validated. Precise phylogenetic investigations using various molecular markers and specimens from diverse regions are definitely needed to provide an exact evolutionary concept on this phylum.

Non-carnivorous feeding in Arctic chaetognaths

Chaetognaths (arrow worms) are important components of zooplankton communities in terms of abundance, biomass and contribution to carbon export. Though traditionally considered strict carnivores, recent studies have identified “omnivorous” chaetognaths. These may feed on non-animal materials, including algae, detritus or sediments. The feeding strategies of the Arctic species Eukrohnia hamata and Parasagitta elegans are particularly interesting given differences in their vertical distributions, and the strong seasonality (peaks and troughs) in the abundance of expected prey items, such as copepods. We analyse the feeding history of these chaetognaths in the Beaufort and Chukchi Seas, and Baffin Bay, using gut contents (types and colours) as short-term signals (days), and biochemistry (stable isotope, lipid and fatty acid composition) as signals integrated over the longer-term (weeks to months), to investigate seasonality in diets and determine the extent to which animal and non-animal matter are consumed. Between November 2007 and July 2008 in the Beaufort Sea, green detritus and oil droplets were abundant in the guts of only E. hamata and were found to contain evidence of diatoms. Weak differences in apparent predation rates and prey items for the two species, but high amounts of green detritus and silica in E. hamata guts point towards direct ingestion of diatoms and marine snow at both epi- and meso-pelagic depths, and can explain δ15N and δ13C-contents that may predict omnivory in the Chukchi Sea and Baffin Bay (fall 2014). Dietary signals in P. elegans predict that this species has a reduced dependence on diatom source pathways relative to E. hamata, for instance a relative absence in green material in guts, and a lower 16:1 (n − 7) concentration. Whilst nitrogen isotopes and fatty acid biomarkers suggested a more carnivorous diet, they also suggest that Calanus copepods are less important to its diet than other types of zooplankters. We suggest that E. hamata (whether pelagic or hyper-benthic) likely receives a substantial energy input from algae and detritus and is thus not a strict carnivore. Our data provide the stimulus for continued focus on these organisms and the important role they play in carbon flux as we try to better understand carbon cycling in a changing Arctic Ocean.

Pathways of Pelagic Connectivity: Eukrohnia hamata (Chaetognatha) in the Arctic Ocean

The dramatic warming of the Arctic Ocean will impact pelagic ecosystems in complex ways, including shifting patterns of species distribution and abundance, and altering migration pathways and population connectivity. The Phylum Chaetognatha (arrow worms) are abundant in the zooplankton assemblage and are highly effective predators, with key roles in pelagic food webs. They are useful indicator species for impacts of climate change on marine ecosystems. This study examined the population genetic diversity, structure and connectivity of the chaetognath, Eukrohnia hamata, based on sampling from six regions defined by geography, bathymetry, and major currents flowing through the Arctic Ocean. A 650-bp region of mitochondrial cytochrome oxidase I (mtCOI) sequenced for 130 specimens resulted in 78 haplotypes and very high haplotype diversity. Analysis of mtCOI haplotype frequencies provided no evidence of population genetic structure. Genomic Single Nucleotide Polymorphisms (SNPs) detected from the same specimens by double-digest Restriction-Associated Digestion (ddRAD) confirmed high levels of gene flow among the regions, but supported the genetic distinctiveness of two population clusters: Atlantic-Arctic versus Pacific-Arctic. Removal of SNPs subject to selection resulted in slightly higher probability of three clusters, and suggested the possibility of local adaptation of regional populations of E. hamata. Comparative analysis revealed evidence that random selection of subsets of SNPs, perhaps impacted by different ecological and (micro) evolutionary drivers, can result in marked differences in numbers and distributional patterns of clusters and associated variation in F-statistics. Analysis of population connectivity using SNPs supported the primary migration pathway via flow from the Atlantic to the Pacific Arctic regions.

First record of a tanaidacean crustacean fed upon by an arrow worm (Chaetognatha)

First record of a tanaidacean crustacean fed upon by an arrow worm (Chaetognatha)

Evolution: Arrow Worms Find Their Place on the Tree of Life

A new phylogenomic study places the erstwhile enigmatic chaetognaths, also known as 'arrow worms', within a subgroup of lophotrochozoans, the gnathiferans.

A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans

Chaetognaths (arrow worms) are an enigmatic group of marine animals whose phylogenetic position remains elusive, in part because they display a mix of developmental and morphological characters associated with other groups [1, 2]. In particular, it remains unclear whether they are a sister group to protostomes [1, 2], one of the principal animal superclades, or whether they bear a closer relationship with some spiralian phyla [3, 4]. Addressing the phylogenetic position of chaetognaths and refining our understanding of relationships among spiralians are essential to fully comprehend character changes during bilaterian evolution [5]. To tackle these questions, we generated new transcriptomes for ten chaetognath species, compiling an extensive phylogenomic dataset that maximizes data occupancy and taxonomic representation. We employed inference methods that consider rate and compositional heterogeneity across taxa to avoid limitations of earlier analyses [6]. In this way, we greatly improved the resolution of the protostome tree of life. We find that chaetognaths cluster together with rotifers, gnathostomulids, and micrognathozoans within an expanded Gnathifera clade and that this clade is the sister group to other spiralians [7, 8]. Our analysis shows that several previously proposed groupings are likely due to systematic error, and we propose arevised organization of Lophotrochozoa with threemain clades: Tetraneuralia (mollusks and entoprocts), Lophophorata (brachiopods, phoronids, and ectoprocts), and a third unnamed clade gathering annelids, nemerteans, and platyhelminthes. Consideration of classical morphological, developmental, and genomic characters in light of this topology indicates secondary loss as a fundamental trend in spiralian evolution.

Ultrastructure of Meelsvirus: A nuclear virus of arrow worms (phylum Chaetognatha) producing giant "tailed" virions.

Most known giant viruses, i.e., viruses producing giant virions, parasitize amoebae and other unicellular eukaryotes. Although they vary in the level of dependence on host nuclear functions, their virions self-assemble in the host cell’s cytoplasm. Here we report the discovery of a new prototype of giant virus infecting epidermal cells of the marine arrow worm Adhesisagitta hispida. Its 1.25 μm-long virions self-assemble and accumulate in the host cell’s nucleus. Conventional transmission electron microscopy reveals that the virions have a unique bipartite structure. An ovoid nucleocapsid, situated in a broad “head” end of the virion is surrounded by a thin envelope. The latter extends away from the head to form a voluminous conical “tail” filled with electron-dense extracapsidular material. The 31nm-thick capsid wall has a distinctive substructure resulting from a patterned arrangement of subunits; it bears no ultrastructural resemblance to the virion walls of other known giant viruses. The envelope self-assembles coincident with the capsid and remotely from all host membranes. We postulate that transmission to new hosts occurs by rupture of protruding virion-filled nuclei when infected arrow worms mate. Future genomic work is needed to determine the phylogenetic position of this new virus, which we have provisionally named Meelsvirus.

Flow generation by the corona ciliata in Chaetognatha − quantification and implications for current functional hypotheses

The corona ciliata of Chaetognatha (arrow worms) is a circular or elliptical groove lined by a rim from which multiple lines of cilia emanate, located dorsally on the head and/or trunk. Mechanoreception, chemosensation, excretion, respiration, and support of reproduction have been suggested to be its main functions. Here we provide the first experimental evidence that the cilia produce significant water flow, and the first visualisation and quantification of this flow. In Spadella cephaloptera, water is accelerated toward the corona ciliata from dorsal and anterior of the body in a funnel-shaped pattern, and expelled laterally and caudally from the corona, with part of the water being recirculated. Maximal flow speeds were approximately 140μms−1 in adult specimens. Volumetric flow rate was Q=0.0026μls−1. The funnel-shaped directional flow can possibly enable directional chemosensation. The flow measurements demonstrate that the corona ciliata is well suited as a multifunctional organ.

A Large Cambrian Chaetognath with Supernumerary Grasping Spines

Chaetognaths (arrow worms) are a separate phylum (Chaetognatha) of small carnivorous animals, dominantly pelagic, and a major component of today's plankton [1, 2]. The position of Chaetognatha among metazoan phyla remains equivocal-neither morphological nor molecular data provide definitive evidence [3]. Originating early in the Cambrian period [4], if not earlier [5], chaetognaths quickly became important members of marine metazoan communities [6]. Chaetognath grasping spines, originally reported as conodonts, occur worldwide in many Cambrian marine sediments [6, 7]. Fossilized chaetognath bodies, in contrast, are very rare: only two unequivocal specimens have been reported, both from the early Cambrian of China [8, 9]. Here we describe Capinatator praetermissus, a new genus and species, based on ∼50 specimens from several middle Cambrian Burgess Shale localities in British Columbia, many of which preserve evidence of soft tissues. Capinatator praetermissus reached body lengths of nearly 10cm exclusive of fins, a much larger size than that of most living forms. Clusters of specimens preserving the body indicate that they were rapidly buried, providing indirect evidence that they swam near the seabed. The feeding apparatus comprises up to ∼25 spines in each half, almost double the maximum number in living chaetognaths. Early chaetognaths apparently occupied ecological niches associated with predatory euarthropods. The large body size and high number of grasping spines in C.praetermissus may indicate that miniaturization and migration to a planktonic lifestyle were secondary.