The Taxonomical Outline of Chaetognatha

Tokioka, Takasi

doi:10.5134/175381

Cited by 54 publications

(54 citation statements)

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“…Similar to the ventral nerve center (compare Harzsch et al 2009), the pattern of RFir neurons in the brain of Pterosagitta draco corresponds more to that of Sagittidae than to Spadellidae. This result is consistent with the traditional phylogeny (e.g., Tokioka 1965a; Salvini‐Plawen 1986), mainly based on the presence or absence of transverse muscles (phragms). However, on the basis of the 18S rRNA analysis (Papillon et al 2006), the Spadellidae appear as a paraphyletic assemblage, from which P. draco , a species without phragms, derives.…”

Section: Discussionsupporting

confidence: 90%

Immunohistochemical analysis and 3D reconstruction of the cephalic nervous system in Chaetognatha: insights into the evolution of an early bilaterian brain?

Rieger

Perez

Müller

et al. 2010

Invertebrate Biology

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Abstract. We examined the brain architecture in different species of Chaetognatha using immunofluorescence methods with a set of nervous system markers and confocal laser‐scan microscopic analysis. These markers include antibodies against synaptic proteins, RFamide‐related peptides, and tyrosinated tubulin, as well as a marker of cell nuclei. Furthermore, we present a 3D reconstruction based on histological section series. Our results expand the previous knowledge on neuroanatomy in Chaetognatha. We suggest a structural and functional subdivision of the rather complex chaetognath brain into two domains, a posterior domain that may be primarily involved in the integration of sensory input, and an anterior domain that may be involved in the control of the mouthparts and the anterior part of the digestive system. Immunolocalization of a neuropeptide suggests the presence of an identifiable group of neurons associated with the brain of all species examined here. However, our data also reveal a certain degree of interspecific variation and divergence within the Chaetognatha concerning, for example, the pattern of nerves branching off the brain and the proportional sizes of the various neuropil compartments. We compare our data to brain architecture in various other representatives of Protostomia and Deuterostomia. The chaetognath brain fits within the range of structural variation encountered in protostomian brains, and we cannot find any brain characteristics that would argue in favor of placing chaetognaths outside of the Protostomia. Rather, we see the circumoral arrangement of their cephalic nervous system as an argument that suggests protostome affinities.

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Section: Discussionsupporting

confidence: 90%

Immunohistochemical analysis and 3D reconstruction of the cephalic nervous system in Chaetognatha: insights into the evolution of an early bilaterian brain?

Rieger

Perez

Müller

et al. 2010

Invertebrate Biology

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“…These two taxa were characterized by Tokioka (1965) based on the presence (Phragmophora) and absence (Aphragmophora) of transverse muscles (phragms). A recent molecular analysis of the intraphyletic relationships has revealed the variability of this character (homoplasy) and highlighted the inXuence of the life style on chaetognath morphology, particularly for benthic species that adapt to a planktonic lifestyle (Papillon et al 2006).…”

Section: Resultsmentioning

confidence: 99%

Fine structure of the ventral nerve centre and interspecific identification of individual neurons in the enigmatic Chaetognatha

et al. 2008

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The enigmatic arrow worms (Chaetognatha) are marine carnivores and among the most abundant planktonic organisms. Their phylogenetic position has been heavily debated for a long time. Most recent molecular studies still provide a diverging picture and suggest arrow worms to be some kind of basal protostomes. In an eVort to understand the organization of the nervous system in this clade for a broad comparison with other Metazoa we analysed the ultrastructure of the ventral nerve centre in Spadella cephaloptera by transmission electron microscopy. We were able to identify six diVerent types of neurons in the bilateral somata clusters by means of the cytoplasmic composition (regarding the structure of the neurite and soma including the shape and eu-/heterochromatin ratio within the nucleus) as well as the size and position of these neurons. Furthermore, our study provides new insights into the neuropil composition of the ventral nerve centre and several other Wne structural features. Our second goal was to examine if individually identiWable neurons are present in the ventral nerve centres of four chaetognath species, Sagitta setosa, Sagitta enXata, Pterosagitta draco, and Spadella cephaloptera. For that purpose, we processed whole mount specimens of these species for immunolocalization of RFamiderelated neuropeptides and analysed them with confocal laser-scanning microscopy. Our experiments provide evidence for the interspeciWc homology of individual neurons in the ventral nerve centres of these four chaetognath species suggesting that the potential to generate serially arranged neurons with individual identities is part of their ground pattern.

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“…The highest taxonomic division within the class Sagittoidae within the Chaetognatha is generally proposed to be into the orders Phragmophora and Aphragmophora (Tokioka 1965a(Tokioka ,b, 1974. The former (including the genera Spadella and Eukrohnia) are chaetognaths possessing an internal sheet of transverse musculature or phragma not found in the Aphragmophora (the genus Sagitta in this study).…”

Section: Phylogenetic Conclusion I: Phragmophora and Aphragmophoramentioning

confidence: 99%

Evolution of 28S Ribosomal DNA in Chaetognaths: Duplicate Genes and Molecular Phylogeny

Telford

Holland

1997

J Mol Evol

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The chaetognaths are an extraordinarily homogeneous phylum of animals at the morphological level, with a bauplan that can be traced back to the Cambrian. Despite the attention of zoologists for over two centuries, there is little agreement on classification within the phylum. We have used a molecular biological approach to investigate the phylogeny of extant chaetognaths. A rapidly evolving expansion segment toward the 5' end of 28S ribosomal DNA (rDNA) was amplified using the polymerase chain reaction (PCR), cloned, and sequenced from 26 chaetognath samples representing 18 species. An unusual finding was the presence of two distinct classes of 28S rDNA gene in chaetognaths; our analyses suggest these arose by a gene (or gene cluster) duplication in a common ancestor of extant chaetognaths. The two classes of chaetognath 28S rDNA have been subject to different rates of molecular evolution; we present evidence that both are expressed and functional. In phylogenetic reconstructions, the two classes of 28S rDNA yield trees that root each other; these clearly demonstrate that the Aphragmophora and Phragmophora are natural groups. Within the Aphragmophora, we find good support for the groupings denoted Solidosagitta, Parasagitta, and Pseudosagitta. The relationships between several well-supported groups within the Aphragmophora are uncertain; we suggest this reflects rapid, recent radiation during chaetognath evolution.

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The Taxonomical Outline of Chaetognatha

Cited by 54 publications

References 1 publication

Immunohistochemical analysis and 3D reconstruction of the cephalic nervous system in Chaetognatha: insights into the evolution of an early bilaterian brain?

Immunohistochemical analysis and 3D reconstruction of the cephalic nervous system in Chaetognatha: insights into the evolution of an early bilaterian brain?

Fine structure of the ventral nerve centre and interspecific identification of individual neurons in the enigmatic Chaetognatha

Evolution of 28S Ribosomal DNA in Chaetognaths: Duplicate Genes and Molecular Phylogeny

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