Architecture of the nervous system in mystacocarida (Arthropoda, crustacea)—An immunohistochemical study and 3D reconstruction

Abstract

Mystacocarida is a species-poor group of minute crustaceans with unclear phylogenetic affinities. Previous studies have highlighted the putative "primitiveness" of several mystacocarid features, including the architecture of the nervous system. Recent studies on arthropod neuroarchitecture have provided a wealth of characters valuable for phylogenetic reconstructions. To permit and facilitate comparison with these data, we used immunohistochemical labeling (against acetylated alpha-tubulin, serotonin and FMRFamide) on the mystacocarid Derocheilocaris remanei, analyzing it with confocal laser-scanning microscopy and 3D reconstruction. The mystacocarid brain is fairly elongated, exhibiting a complicated stereotypic arrangement of neurite bundles. However, none of the applied markers provided evidence of structured neuropils such as a central body or olfactory glomeruli. A completely fused subesophageal ganglion is not present, all segmental soma clusters of the respective neuromeres still being delimitable. The distinct mandibular commissure comprises neurite bundles from more anterior regions, leading us to propose that it may have fused with an ancestral posterior tritocerebral commissure. The postcephalic ventral nervous system displays a typical ladder-like structure with separated ganglia which bears some resemblance to larval stages in other crustaceans. Ganglia and commissures are also present in the first three limbless "abdominal" segments, which casts doubt on the notion of a clear-cut distinction between thorax and abdomen. An unpaired longitudinal median neurite bundle is present and discussed as a potential tetraconate autapomorphy. Additionally, a paired latero-longitudinal neurite bundle extends along the trunk. It is connected to the intersegmental nerves and most likely fulfils neurohemal functions. We report the complete absence of serotonin-ir neurons in the ventral nervous system, which is a unique condition in arthropods and herein interpreted as a derived character.

Invertebrate neurophylogeny: suggested terms and definitions for a neuroanatomical glossary

“…In Crustacea, a central complex adhering to the architectural scheme found in Insecta has been described in representatives of Malacostraca (Figure 4C; [64,69]), Remipedia [70] and Branchiopoda [71]. Although it is generally thought that the components of the central complex are part of the ground pattern of the Tetraconata [39,64,69-72], the absence of at least some components of the central complex in certain crustaceans might well be interpreted as plesiomorphic [73]. Several lines of evidence suggest that the central complex acts as a higher navigational and locomotor control centre [74,75].…”

“…This phenomenon is widespread in annelids [52]. Interestingly enough, additional median and lateral neurite bundles and ring-like structures are present in the crustacean Derocheilocaris remanei (Mystacocarida; [73]).…”

Serotonin immunoreactive interneurons in the brain of the Remipedia: new insights into the phylogenetic affinities of an enigmatic crustacean taxon

“…These include Branchiopoda, Copepoda and Mystacocarida, all of which lack 5HT-ir interneurons [28,30,31,48]. …”

“…Even though the detailed shape of cephalocaridan olfactory glomeruli was difficult to resolve by immunocytochemical methods, it is certainly not spherical [33]. Studies on Branchiopoda, Copepoda and Mystacocarida revealed that these taxa do not possess ONs and consequently do not have any glomerular structures in the deutocerebrum [30,31,48]. …”

Distribution of C-type allatostatin (C-AST)-like immunoreactivity in the central nervous system of the copepod Calanus finmarchicus

“…The acetylated-α-tubulin antibody has been used extensively to map the distribution of this protein in a number of crustaceans ( e.g. Semmler et al, 2008; Brenneis and Richter, 2010), including C. finmarchicus (Orcine and Hartline, 2010); while not directly tested for C. finmarchicus , the specificity of this monoclonal antibody for acetylated-α-tubulin has demonstrated in many species (for a detailed description of the antibody’s specificity readers are referred to http://datasheets.scbt.com/sc-23950.pdf). However, as our study is the first to use the C-AST antibody on C. finmarchicus neural tissue, preadsorption controls were conducted to assess the specificity of its labeling.…”