Ctenophora is an early‐branching basal metazoan lineage, which may have evolved neurons and muscles independently from other animals. However, despite the profound diversity among ctenophores, basal neuroanatomical data are limited to representatives of two genera. Here, we describe the organization of neuromuscular systems in eight ctenophore species focusing on
Cnidaria is the sister taxon to bilaterian animals, and therefore, represents a key reference lineage to understand early origins and evolution of the neural systems. The hydromedusa
- NSF-PAR ID:
- 10457665
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Comparative Neurology
- Volume:
- 528
- Issue:
- 7
- ISSN:
- 0021-9967
- Page Range / eLocation ID:
- p. 1231-1254
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Euplokamis dunlapae —the representative of the lineage sister to all other ctenophores. Cydippids (Hormiphora hormiphora andDryodora glandiformis ) and lobates (Bolinopsis infundibulum andMnemiopsis leidyi ) were used as reference platforms to cover both morphological and ecological diversity within the phylum. We show that even with substantial environmental differences, the basal organization of neural systems is conserved among ctenophores. In all species, we detected two distributed neuronal subsystems: the subepithelial polygonal network and the mesogleal elements. Nevertheless, each species developed specific innovations in neural, muscular, and receptor systems. Most notableEuplokamis ‐specific features are the following: (a) Comb nerves with giant axons. These nerves directly coordinate the rapid escape response bypassing the central integrative structure known as the aboral sensory organ. (b) Neural processes in tentacles along the rows of “boxes” providing structural support and located under striated muscles. (c) Radial muscles that cross the mesoglea and connect the outer wall to the aboral canal. (d) Flat muscles, encircling each meridional canal. Also, we detected a structurally different rectangular neural network in the feeding lobes of Lobata (Mnemiopsis/Bolinopsis ) but not in other species. The described lineage‐specific innovations can be used for future single‐cell atlases of ctenophores and analyses of neuronal evolution in basal metazoans. -
Abstract Ctenophores are descendants of one of the earliest branching metazoan lineage with enigmatic nervous systems. The lack of convenient neurogenic molecules and neurotransmitters suggests an extensive parallel evolution and independent origins of neurons and synapses. However, the field lags due to the lack of microanatomical data about the neuro‐muscular systems in this group of animals. Here, using immunohistochemistry and scanning electron microscopy, we describe the organization of both muscular and nervous systems in the sea gooseberry,
from North Pacific. The diffuse neural system ofPleurobrachia bachei ,Pleurobrachia consists of two subsystems: the subepithelial neural network and the mesogleal net with about 5,000–7,000 neurons combined. Our data revealed the unexpected complexity of neuromuscular organization in this basal metazoan lineage. The anatomical diversity of cell types includes at least nine broad categories of neurons, five families of surface receptors and more than two dozen types of muscle cells as well as regional concentrations of neuronal elements to support ctenophore feeding, complex swimming, escape, and prey capture behaviors. In summary, we recognize more than 80 total morphological cell types. Thus, in terms of cell‐type specification and diversity, ctenophores significantly exceed what we currently know about other prebilaterian groups (placozoan, sponges, and cnidarians), and some basal bilaterians. -
Abstract Ctenophores are descendants of an early branching basal metazoan lineage, which may have evolved neurons and muscles independently from other animals.
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