Invertebrate nervous systems are highly disparate between different taxa. This is reflected in the terminology used to describe them, which is very rich and often confusing. Even very general terms such as 'brain', 'nerve', and 'eye' have been used in various ways in the different animal groups, but no consensus on the exact meaning exists. This impedes our understanding of the architecture of the invertebrate nervous system in general and of evolutionary transformations of nervous system characters between different taxa. We provide a glossary of invertebrate neuroanatomical terms with a precise and consistent terminology, taxon-independent and free of homology assumptions. This terminology is intended to form a basis for new morphological descriptions. A total of 47 terms are defined. Each entry consists of a definition, discouraged terms, and a background/comment section. The use of our revised neuroanatomical terminology in any new descriptions of the anatomy of invertebrate nervous systems will improve the comparability of this organ system and its substructures between the various taxa, and finally even lead to better and more robust homology hypotheses.

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Invertebrate neurophylogeny: suggested terms and definitions for a neuroanatomical glossary

The Articulata hypothesis – or what is a segment?

The trochophora concept and the literature on cleavage patterns and differentiation of ectodermal structures in annelids (“polychaetes”) and molluscs are reviewed. The early development shows some variation within both phyla, and the cephalopods have a highly modified development. Nevertheless, there are conspicuous similarities between the early development of the two phyla, related to the highly conserved spiral cleavage pattern. Apical and cerebral ganglia have almost identical origin in the two phyla, and the cell-lineage of the prototroch is identical, except for minor variations between species. The cell-lineage of the metatrochs is almost unknown, but the telotroch of annelids and the “telotroch” of the gastropod Patella originate from the 2d-cell, as does the gastrotroch in the few species which have been studied. The segmented annelid body, i.e. the region behind the peristome, develops through addition of new ectoderm from a ring of 2d-cells just in front of the telotroch. This whole region is thus derived from 2d-cells. Conversely, the mollusc body is covered by descendants of cells from both the C and D quadrants and a growth zone is not apparent. This supports the notion that the molluscs are not segmented like the annelids, and that the repeated structures seen in polyplacophorans and monplacophorans do not represent a segmentation homologous to that of the annelids. J. Exp. Zool. (Mol. Dev. Evol.) 302B: 35–68, 2004. © 2004 Wiley-Liss, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jez.b.20001

Trochophora larvae: cell-lineages, ciliary bands, and body regions. 1. Annelida and Mollusca.

High-resolution fate map of the snail Crepidula fornicata: the origins of ciliary bands, nervous system, and muscular elements.

Despite the large variation in adult bodyplan phenotypes, a worm-shaped morphology is considered plesiomorphic for both Lophotrochozoa and Bilateria. Although almost all larval and adult lophotrochozoan worms have serially arranged ring muscles in their body wall, a comparison of their ontogeny reveals no less than six different developmental pathways that lead to this homogenous arrangement of ring muscles. However, in all taxa, with the exception of chaetodermomorph molluscs and the segmented annelids, ring muscle development starts with synchronous formation of certain pioneer myocytes, which is thus considered basal for Lophotrochozoa. Recent studies on spiralian neurogenesis revealed remnants of ancestral segmentation in echiurans and sipunculans, thus confirming molecular phylogenetic studies that propose a close relationship of these three taxa. Larval entoprocts exhibit a mosaic of larval and adult molluscan characters and, among other apomorphies, share with polyplacophoran Mollusca a complex larval apical organ and a tetraneurous nervous system, strongly suggesting a monophyletic assemblage of Entoprocta and Mollusca. The term Tetraneuralia is proposed herein for this lophotrochozoan clade. Overall, formation of the lophotrochozoan neuromuscular bodyplan appears as a highly dynamic process on both the ontogenetic and the evolutionary timescales, highlighting the importance of insights into these processes for reconstructing ancestral bodyplan features and phylogenetic relationships.

https://www.journals.uchicago.edu/doi/pdf/10.1086/BBLv216n3p293

Shaping the Things to Come: Ontogeny of Lophotrochozoan Neuromuscular Systems and the Tetraneuralia Concept

Neurogenesis in the chiton Mopalia mus- cosa (Gould, 1846) was investigated by applying differen- tial interference contrast microscopy, semithin serial sec- tioning combined with reconstruction techniques, as well as confocal laser scanning microscopy for the detection of fluorescence-conjugated antibodies against serotonin and FMRFamide. The ontogeny of serotonergic nervous struc- tures starts with cells of the apical organ followed by those of the cerebral commissure, whereas the serotonergic pro- totroch innervation, pedal system, and the lateral cords develop later. In addition, there are eight symmetrically arranged serotonergic sensory cells in the dorsal pretro- chal area of the larva. FMRFamide-positive neural ele- ments include the cerebral commissure, specific "ampul- lary" sensory cells in the pretrochal region, as well as the larval lateral and pedal system. In the early juvenile the cerebral system no longer stains with either of the two antibodies and the pedal system lacks anti-FMRFamide immunoreactivity. Outgroup comparison with all other molluscan classes and related phyla suggests that the cord-like, nonganglionized cerebral system in the Polypla- cophora is a reduced condition rather than a primitive molluscan condition. The immunosensitivity of the pedal commissures develops from posterior to anterior, suggest- ing independent serial repetition rather than annelid-like conditions and there is no trace of true segmentation during nervous system development. Polyplacophoran neurogenesis and all other available data on the subject contradict the idea of a segmented molluscan stem spe- cies. J. Morphol. 253:109 -117, 2002. © 2002 Wiley-Liss, Inc.

Neurogenesis in the mossy chiton, Mopalia muscosa (Gould) (Polyplacophora): evidence against molluscan metamerism.

Combined electron microscopy and immunocytochemistry of the larvae of several polyplacophoran species (Chiton olivaceus, Lepidochitona aff. corrugata, Mopalia muscosa) revealed a sensory system new to science, a so-called “ampullary system.” The cells of the “ampullary system” are arranged in four symmetrically situated pairs lying dorsolaterally and ventrolaterally in the pretrochal part of the trochophore-like larva and they send axons into the cerebral commissure. They are lost at metamorphosis. The fine structure of these cells strongly resembles that of so-called “ampullary cells” known from various sensory organs of other molluscs, such as the apical complex of gastropod and bivalve larvae, osphradia of vetigastropods, and olfactory organs of cephalopods, and nuchal organs of certain polychaetes. The ampullary cells and their nerves are densely stained by anti-FMRF-amide fluorescence dyes, whereas antiserotonin staining is only weak. While cytological homology of the ampullary cells with those of other organs is probable, the ampullary system as a whole is regarded as a synapomorphy of the Polyplacophora or Chitonida. J. Morphol. 251:210–218, 2002. © 2002 Wiley-Liss, Inc.

Fine structure and immunocytochemistry of a new chemosensory system in the chiton larva (Mollusca: Polyplacophora)

The genus Ceratobates (Oribatida, Tegoribatidae) is recorded in Peruvian fauna for the first time. Ceratobates pachiteaensis sp. n., a new species, is described based on materials collected from soil and leaf litter in the Andean mountain forests. The main generic traits are summarized, and an identification key to known species of Ceratobates is provided.

A new species of Ceratobates (Acari, Oribatida) from Peru and a key to known species of the genus

ABSTRACT One new species of Hermannobates (Oribatida, Hermanniellidae) – H. magnus sp. nov. – is described, based on materials collected from upper soil and leaf litter in mountain forests of Andean Peru. A generic diagnosis, identification key, distribution, and habitats of representatives of Hermannobates are presented. http://www.zoobank.org/urn:lsid:zoobank.org:pub:E0F6D444-9EC8-4837-A57D-81A5C95C73E4

Contribution to the knowledge of the oribatid mite genus Hermannobates (Acari, Oribatida, Hermanniellidae)

ABSTRACT The genus Suctoribates is recorded in Peruvian fauna for the first time. Two new species of Suctoribates (Oribatida, Rhynchoribatidae) – Suctoribates goebelae sp. nov. and S. monzoni sp. nov. – are described based on materials collected from upper soil and leaf litter in forests of Andean Peru. Generic diagnosis and identification key to representatives of Suctoribates are presented. http://urn:lsid:zoobank.org:pub:DEAB7711-4B6F-4F32-8070-CB402B742579

Contribution to the knowledge of the oribatid mite genus Suctoribates (Acari, Oribatida, Rhynchoribatidae), with description of two new species from Peru

Stefan Friedrich

Papers

Neurogenesis in the mossy chiton, Mopalia muscosa (Gould) (Polyplacophora): evidence against molluscan metamerism.

Fine structure and immunocytochemistry of a new chemosensory system in the chiton larva (Mollusca: Polyplacophora)

A new species of Ceratobates (Acari, Oribatida) from Peru and a key to known species of the genus

Contribution to the knowledge of the oribatid mite genus Hermannobates (Acari, Oribatida, Hermanniellidae)

Contribution to the knowledge of the oribatid mite genus Suctoribates (Acari, Oribatida, Rhynchoribatidae), with description of two new species from Peru