Abstract
The neuropeptide FMRFamide (Phe–Met–Arg–Phe–NH2) is part of a large and diverse family of peptidergic neurotransmitters present throughout the animal kingdom. To date, no such neuropeptides have been demonstrated in gastrotrichs despite their presence in closely related invertebrates such as nematodes. Here, the FMRFamidergic nervous system of three marine gastrotrichs is investigated with immunofluorescence, CLSM, and 3D computer imaging to gain insight into structure of the cerebral ganglion and test various phylogenetic hypotheses on its organization. Results reveal that FMRFamide-like immunoreactivity (IR) is present throughout the nervous systems of three species: Neodasys cirritus (Chaetonotida), Xenodasys riedli and Turbanella cf. hyalina (Macrodasyida). Both macrodasyidans possess FMRFamide-like IR in the central, peripheral- and stomatogastric-nervous systems, while FMRFamide-like IR is restricted to the CNS in N. cirritus. In all three species, the cerebral ganglion is dumbbell-shaped and bordered bilaterally by cerebral perikarya: numerous perikarya are present in X. riedli and N. cirritus, while few perikarya are present in T. cf. hyalina. Cerebral perikarya flank the nerve ring neuropil, which contains IR fibers in the supra- and subpharyngeal commissures of both macrodasyidans, but in N. cirritus, only contains IR fibers in the suprapharyngeal commissure. Together, these results confirm the peripharyngeal nature of the gastrotrich cerebral ganglion, but are equivocal on hypotheses of its tripartite structure. Still, the neural organization of gastrotrichs, in particular, the architecture of the cerebral ganglion, is expected to hold valuable information for future assessments of gastrotrich phylogeny, and may yet provide key insights into the evolution of this enigmatic taxon.
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The author is grateful for the comments by two anonymous reviewers that improved this manuscript. The author is also grateful to the staff at the Smithsonian Marine Station in Fort Pierce, Florida for their assistance in collection and the use of their facilities. This research received financial support from the University of Massachusetts Lowell and from the Sumner Gerard Foundation at the Smithsonian Marine Station at Fort Pierce, Florida. This is Smithsonian Marine Station at Fort Pierce contribution 706.
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Hochberg, R. Comparative immunohistochemistry of the cerebral ganglion in Gastrotricha: an analysis of FMRFamide-like immunoreactivity in Neodasys cirritus (Chaetonotida), Xenodasys riedli and Turbanella cf. hyalina (Macrodasyida). Zoomorphology 126, 245–264 (2007). https://doi.org/10.1007/s00435-007-0044-2
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DOI: https://doi.org/10.1007/s00435-007-0044-2