A morphological and molecular reinvestigation of Janickina pigmentifera (Grassi, 1881) Chatton 1953 - an amoebozoan parasite of arrow-worms (Chaetognatha).

Amoebozoan parasites of arrow-worms (Chaetognatha) were isolated from their hosts living in plankton of the Bay of Villefranche (Mediterranean Sea). Based on the light microscopic characters, the amoebae were identified as Janickina pigmentifera (Grassi, 1881) by their limax locomotive form and due to the presence of the intracellular symbiont, Perkinsela amoebae, surrounded by a layer of pigment granules. Sequences of the 18S rRNA gene of both J. pigmentifera and its symbiont were obtained for the first time. The molecular phylogenetic analyses of 18S rRNA gene placed J. pigmentifera within the genus Neoparamoeba, a taxon also characterized by the presence of a symbiont, known as Perkinsela amoebae-like organism (PLO). The 18S rRNA gene sequence of P. amoebae from J. pigmentifera grouped with the sequences of 18S rRNA genes of PLOs from Neoparamoeba branchiphila and Neoparamoeba invadens. The first photo documentation of the light microscopic features of J. pigmentifera, such as locomotive form, the morphology of the nucleus and P. amoebae have been provided. The new results support the affinity of J. pigmentifera with the family Paramoebidae suggested previously based on the presence of PLO. In contrast to Janickina, typical members of Paramoebidae (Neoparamoeba and Paramoeba) have a flattened, dactylopodial locomotive form. This discrepancy in morphology can be explained by the obligate parasitic lifestyle of Janickina.

Evolutionary history of Chaetognatha inferred from molecular and morphological data: a case study for body plan simplification.

BACKGROUND: Chaetognatha are a phylum of marine carnivorous animals which includes more than 130 extant species. The internal systematics of this group have been intensively debated since it was discovered in the 18(th) century. While they can be traced back to the earlier Cambrian, they are an extraordinarily homogeneous phylum at the morphological level - a fascinating characteristic that puzzled many a scientist who has tried to clarify their taxonomy. Recent studies which have attempted to reconstruct a phylogeny using molecular data have relied on single gene analyses and a somewhat restricted taxon sampling. Here, we present the first large scale phylogenetic study of Chaetognatha based on a combined analysis of nearly the complete ribosomal RNA (rRNA) genes. We use this analysis to infer the evolution of some morphological characters. This work includes 36 extant species, mainly obtained from Tara Oceans Expedition 2009/2012, that represent 16 genera and 6 of the 9 extant families. RESULTS: Cladistic and phenetic analysis of morphological characters, geometric morphometrics and molecular small subunit (SSU rRNA) and large subunit (LSU rRNA) ribosomal genes phylogenies provided new insights into the relationships and the evolutionary history of Chaetognatha. We propose the following clade structure for the phylum: (((Sagittidae, Krohnittidae), Spadellidae), (Eukrohniidae, Heterokrohniidae)), with the Pterosagittidae included in the Sagittidae. The clade (Sagittidae, Krohnittidae) constitutes the monophyletic order of Aphragmophora. Molecular analyses showed that the Phragmophora are paraphyletic. The Ctenodontina/Flabellodontina and Syngonata/Chorismogonata hypotheses are invalidated on the basis of both morphological and molecular data. This new phylogeny also includes resurrected and modified genera within Sagittidae. CONCLUSIONS: The distribution of some morphological characters traditionally used in systematics and for species diagnosis suggests that the diversity in Chaetognatha was produced through a process of mosaic evolution. Moreover, chaetognaths have mostly evolved by simplification of their body plan and their history shows numerous convergent events of losses and reversions. The main morphological novelty observed is the acquisition of a second pair of lateral fins in Sagittidae, which represents an adaptation to the holoplanktonic niche.

In situ microplastic ingestion by neritic zooplankton of the central Mexican Pacific.

Microplastics (MPs) are present across the global ocean and can be encountered by many species, including zooplankton. Although they fall within the size range of zooplankton prey, there are few studies on MPs ingestion carried out in situ. In this study, we analyzed MPs ingestion during two seasons (rainy and dry) of organisms from 5 taxonomic groups of zooplankton from two bays of the Mexican central Pacific: Manzanillo and Navidad. In total, 2643 individuals were analyzed, and of those 23 individuals contained MPs. The ingestion rate by taxonomic group was 1 MP/36 copepods (0.02), 1 MP/30 decapods-mysis (0.03), 1 MP/29 decapods-megalopa (0.03), and 1 MP/200 fish larvae (0.005). No plastics were found in chaetognaths, amphipods, or decapods-zoea. The average length of the ingested particles was 468.1 ± 113.8 µm, with a minimum of 15.6 and a maximum of 647.6 µm. All MPs >300 µm were fibers, with diameters <50 µm. Fragments were the most abundant MPs (54.2%), followed by fibers (34.2%) and spheres (11.4%). Statistical analyses showed no significant differences (p > 0.05) between the bays or seasons. Using RAMAN spectroscopy, it was possible to identify 6 different types of polymers, with poly (ethylene:propylene) being the most abundant (42.8%). This polymer is commonly used to manufacture plastic bags, ropes and fishing nets. The results confirm that certain zooplankton groups are consuming MPs and suggest that omnivorous species are more likely to ingest MPs, possibly due to their capacity for foraging flexibility and opportunistic feeding strategies. However, the ingestion of MPs cannot be attributed to a single factor; it is necessary to consider variables such as the sampling area, feeding strategy, size, and seasonality to understand the dynamics of MPs ingestion by zooplankton groups.

Validation of Spadella kappae Schmidt-Rhaesa amp; Vieler, a small benthic chaetognath from Roscoff, France (Chaetognatha).

Schmidt-Rhaesa Vieler (2018) described a new species of benthic chaetognath, Spadella kappae, collected by meiofaunal sampling near Roscoff, France. Although the description and figures presented by Schmidt-Rhaesa Vieler (2018) fully characterize the new species, the journal issue in which the description appeared was published online-only, with no print version, and the article in which the new name appeared did not include a ZooBank registration number for the article (LSID), required for validation of new species names in electronic-only publications (ICZN 2012). As a result, the name Spadella kappae Schmidt-Rhaesa Vieler, 2018, as published in Cahiers de Biologie Marine 59: 257-265, is not available according the International Code of Zoological Nomenclature, hereafter, the Code (ICZN 1999, 2012). Therefore, the present note serves to validate the name Spadella kappae by fulfilling Code conditions for nomenclatural availability. The date and authorship of the specific name, accordingly, are those of this note, not Schmidt-Rhaesa Vieler (2018).

Bilateral Jaw Elements in Amiskwia sagittiformis Bridge the Morphological Gap between Gnathiferans and Chaetognaths.

Amiskwia sagittiformis Walcott 1911 is an iconic soft-bodied taxon from the Burgess Shale [1-3]. It was originally interpreted as a chaetognath [1], but it was later interpreted as a pelagic nemertean [2] or considered of uncertain affinity [3]. Part of this ambiguity is due to direct comparisons with members of the crown groups of extant phyla [4] and a lack of clarity regarding the systematic position of chaetognaths, which would allow for assessing character polarity in the phylum with respect to outgroups. Here, we show that Amiskwia preserves a bilaterally arranged set of head structures visible in relief and high reflectivity. These structures are best interpreted as jaws situated within an expanded pharyngeal complex. Morphological studies have highlighted a likely homology between bilateral and chitinous jaw elements in gnathiferans and chaetognaths [5], which is congruent with a shared unique Hox gene that suggests a close relationship between Gnathifera and Chaetognatha [6]. Molecular phylogenetic studies have recently found gnathiferans to be a deep branch of Spiralia and Chaetognaths either a sister group to Spiralia [7] or forming a clade with gnathiferans [6, 8]. Our phylogenetic analyses render Gnathifera paraphyletic with respect to Chaetognatha, and we therefore suggest that Amiskwia is best interpreted as a stem chaetognath, but crown gnathiferan.

Extreme Mitogenomic Variation in Natural Populations of Chaetognaths.

The extent of within-species genetic variation across the diversity of animal life is an underexplored problem in ecology and evolution. Although neutral genetic variation should scale positively with population size, mitochondrial diversity levels are believed to show little variation across animal species. Here, we report an unprecedented case of extreme mitochondrial diversity within natural populations of two morphospecies of chaetognaths (arrow worms). We determine that this diversity is composed of deep sympatric mitochondrial lineages, which are in some cases as divergent as human and platypus. Additionally, based on 54 complete mitogenomes, we observed mitochondrial gene order differences between several of these lineages. We examined nuclear divergence patterns (18S, 28S, and an intron) to determine the possible origin of these lineages, but did not find congruent patterns between mitochondrial and nuclear markers. We also show that extreme mitochondrial divergence in chaetognaths is not driven by positive selection. Hence, we propose that the extreme levels of mitochondrial variation could be the result of either a complex scenario of reproductive isolation, or a combination of large population size and accelerated mitochondrial mutation rate. These findings emphasize the importance of characterizing genome-wide levels of nuclear variation in these species and promote chaetognaths as a remarkable model to study mitochondrial evolution.

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.

Cryptic tRNAs in chaetognath mitochondrial genomes.

The chaetognaths constitute a small and enigmatic phylum of little marine invertebrates. Both nuclear and mitochondrial genomes have numerous originalities, some phylum-specific. Until recently, their mitogenomes seemed containing only one tRNA gene (trnMet), but a recent study found in two chaetognath mitogenomes two and four tRNA genes. Moreover, apparently two conspecific mitogenomes have different tRNA gene numbers (one and two). Reanalyses by tRNAscan-SE and ARWEN softwares of the five available complete chaetognath mitogenomes suggest numerous additional tRNA genes from different types. Their total number never reaches the 22 found in most other invertebrates using that genetic code. Predicted error compensation between codon-anticodon mismatch and tRNA misacylation suggests translational activity by tRNAs predicted solely according to secondary structure for tRNAs predicted by tRNAscan-SE, not ARWEN. Numbers of predicted stop-suppressor (antitermination) tRNAs coevolve with predicted overlapping, frameshifted protein coding genes including stop codons. Sequence alignments in secondary structure prediction with non-chaetognath tRNAs suggest that the most likely functional tRNAs are in intergenic regions, as regular mt-tRNAs. Due to usually short intergenic regions, generally tRNA sequences partially overlap with flanking genes. Some tRNA pairs seem templated by sense-antisense strands. Moreover, 16S rRNA genes, but not 12S rRNAs, appear as tRNA nurseries, as previously suggested for multifunctional ribosomal-like protogenomes.

Evolution of Synonymous Codon Usage in the Mitogenomes of Certain Species of Bilaterian Lineage with Special Reference to Chaetognatha.

Chaetognatha is a minor phylum, comprising transparent marine invertebrates varying in size from 0.5 to 12 cm. The exact phylogenetic position of Chaetognatha in Metazoa has not been deciphered as some embryological characteristics place chaetognaths among deuterostomes and some morphological characteristics place these among protostomes. In this study, the major factors that drive synonymous codon usage bias (SCUB) in the mitogenomes of representative species of Chaetognatha and chosen species of other closely related phyla were analyzed. Spearman's rank correlation analyses of nucleotide contents suggested that mutational pressure and selection were acting in all examined mitogenomes but with varying intensities. The quantification of SCUB using effective number of codons vs. GC composition at the third codon position (GC3) plot suggested that mutational pressure due to GC compositional constraints might be one of the major influencing forces driving the SCUB in all chaetognaths except Sagitta enflata. However, neutrality plots revealed no significant correlation between GC3 and cumulative GC content at first and second codon positions (GC12) in all other species, except in Daphnia pulex. The parity rule 2 bias plot showed that significant compositional differences existed between C and G, as well as between A and T, contents in most of the protein-coding genes (PCGs) and, comparatively, A and T contents were used more proportionally than C and G contents in all chosen mitogenomes. Chi-square analysis revealed the presence of putative optimal codons in all species, except in S. enflata. The correspondence analysis identified that mutational pressure and selection act on the mitogenomes of the selected chaetognaths and other phyla with varying intensities. The cluster analysis based on relative synonymous codon usage (RSCU) values revealed that RSCU variations in the PCGs of mitogenomes of chaetognaths are more comparable with those of protostomes. Apart from mutational pressure and selection, certain unknown selective forces might be acting on the PCGs in the analyzed mitogenomes as the phenomenon of SCUB could not be explained by mutational pressure, by selection, or by both.

Transcriptome Analysis of ESTs from a Chaetognath Reveals a Deep-Branching Clade of Retrovirus-Like Retrotransposons.

Chaetognaths constitute a small marine phylum exhibiting several characteristic which are highly unusual in animal genomes, including two classes of both rRNA and protein ribosomal genes. As in this phylum presence of retrovirus-like elements has never been documented, analysis of a published expressed sequence tag (EST) collection of the chaetognath Spadella cephaloptera has been made. Twelve sequences representing transcript sections of reverse transcriptase domain of active retrotransposons were isolated from~11,000 ESTs. Five of them are originated from Gypsy retrovirus-like elements, whereas the other are transcripts from a Bel-Pao LTR-retrotransposon, a Penelope-like element and LINE retrotransposons. Moreover, a part of a putative integrase has also been found. Phylogenetic analyses suggest a deep-branching clade of the retrovirus-like elements, which is in agreement with the probably Cambrian origin of the phylum. Moreover, retrotransposons have not been found in telomeric-like transcripts which are probably constituted by both vertebrate and arthropod canonical repeats.

Checklist do filo Chaetognatha do Estado de São Paulo, Brasil / Checklist of chaetognatha phyllum from São Paulo State, Brazil

O filo Chaetognatha é constituído de um pequeno número de animais marinhos deuterostomados, filogeneticamente isolados, de simetria bilateral e corpo alongado em forma de torpedo ou seta, cujo comprimento pode variar de 2 a 120 mm. O corpo é dividido em três regiões: cabeça, tronco e cauda. A cabeça apresenta um par de olhos e a boca situada no vestíbulo ventral, a qual é circundada por uma coroa de espinhos fortes e por uma ou duas fileiras de dentes. O tronco possui um ou dois pares de nadadeiras laterais e a cauda uma nadadeira na extremidade posterior. São hermafroditas protândricos sendo em geral a fecundação cruzada, interna, e o desenvolvimento direto. São predadores que se alimentam de uma grande variedade de organismos. O canibalismo também é observado no grupo. Os quetógnatos desempenham papel fundamental na teia trófica marinha, como carnívoros primários e item alimentar de organismos planctófagos especialmente peixes de interesse comercial. São considerados bons indicadores de áreas de pesca, potencialmente importantes, grandes produtores de matéria orgânica particulada e peça chave no fluxo do carbono nos oceanos. Mais recentemente, foram reconhecidos como hospedeiros intermediários no ciclo de vida de vários grupos de parasitas marinhos. Os quetógnatos são encontrados em todos os mares, oceanos e regiões estuarinas, sendo mais abundantes entre os 100 e 200 m de profundidade. Com exceção dos componentes da família Spadellidae, que agrupa espécies bentônicas, a grande maioria é planctônica. A distribuição desses organismos é influenciada em geral pelas condições hidrológicas, sendo algumas espécies usadas como indicadoras de massas de água. No momento, 209 espécies de Chaetognatha foram descritas no mundo, das quais 29 ocorrem no Atlântico Sul e 25 em águas brasileiras. No estado de São Paulo, apenas, 14 espécies foram encontradas nas regiões costeiras e oceânicas.

The species of Chaetognatha, commonly called arrow-worms, are considered one of the most taxonomically isolated animal groups, with obscure phyletic origin. They are deuterostomes of small size, between 2 and 12 mm, with bilateral symmetry and transparent torped-shaped body, although some species have pigmentation. The body consists of the head, the trunk and the tail. The head bears a ventrally placed mouth, surrounded by two sets of rigid hooks and rows of small teeth, both used in prey capture. There are two dorsal eyes, which are absents in some deep living species. The trunk bears paired lateral fins and the tail a single fin. They are protandrous hermaphrodites with direct development, being the cross-fertilization probably typical in this phylum. Fertilization is internal and the eggs released directly into the water. Although chaetognaths are eaten by numerous larger carnivorous organisms, in the food web they are important predators and a significant trophic link between small herbivores and larger predators, including important commercial fish species. Cannibalism is known, particularly in some species. They have been recognized as important producers of large quantities of fecal pellets, which must play a significant role in the flux of organic carbon in the oceans. Chaetognaths are also considered good indicators of potentially important fishery areas, and more recently, they gained recognition as vectors in the life cycles of various parasite groups. They are exclusively marine and can be found in all oceans from surface to great depths and in estuarine regions. Generally are most abundant around 100-200 m depths. With exception to the epibenthic family Spadellidae, the chaetognaths are conspicuous members of the zooplankton. Their distribution pattern is influenced by the hydrobiological conditions and some species are known as indicators of water masses. A total of 209 species were recorded in the world's oceans, and 29 for the South Atlantic. Twenty five species are known from the Brazilian waters and only 14 species from coastal and offshore waters of São Paulo State.