dorsal/arxiv
View SchemaHydromechanical considerations on the origin of the pentaradial body structure of echinoderms
| Authors | Michael Gudo |
|---|---|
| Categories | |
| ArXiv ID | q-bio/0505038 |
| URL | https://arxiv.org/abs/q-bio/0505038 |
Abstract
When echinoderms are conceptualized as hydraulic entities, the early evolution of this group can be presented in a scenario which describes how a bilateral ancestor (an enteropneust-like organism) gradually evolved into a pentaradial echinoderm. According to this scenario, the arms are outgrowths from the anterior/posterior body axis of the bilateral pterobranchia-like intermediate. These outgrowths developed when the originally U-shaped mesentery of the intestinal tract formed loops, and correspondingly, the tensile chords of the mesentery were attached to the body wall in five loops. The wall faces between these regions of tensile chords could bulge out under the hydraulic pressure of the body coelom. The originally more or less round body cavity was deformed into a pneu with five bulges. The loops of the gut forced a roughly symmetric arrangement, which was enhanced by a physical fact: five pneus as well as one pneu with five internal tethers, naturally adopt a pentaradial pattern of "minimum contact surfaces", as the most economic arrangement. These evolutionary transformations were accompanied by certain histological modifications, such as the development of mutable connective tissues and skeletal elements that fused to ossicles and provided shape stabilization in the form of a calcareous skeleton in the tissues of the body wall. The resultant organism was an ancestral eleutherozoan echinoderm (Ur-Echinoderm).
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"abstract": "When echinoderms are conceptualized as hydraulic entities, the early\nevolution of this group can be presented in a scenario which describes how a\nbilateral ancestor (an enteropneust-like organism) gradually evolved into a\npentaradial echinoderm. According to this scenario, the arms are outgrowths\nfrom the anterior/posterior body axis of the bilateral pterobranchia-like\nintermediate. These outgrowths developed when the originally U-shaped mesentery\nof the intestinal tract formed loops, and correspondingly, the tensile chords\nof the mesentery were attached to the body wall in five loops. The wall faces\nbetween these regions of tensile chords could bulge out under the hydraulic\npressure of the body coelom. The originally more or less round body cavity was\ndeformed into a pneu with five bulges. The loops of the gut forced a roughly\nsymmetric arrangement, which was enhanced by a physical fact: five pneus as\nwell as one pneu with five internal tethers, naturally adopt a pentaradial\npattern of \"minimum contact surfaces\", as the most economic arrangement. These\nevolutionary transformations were accompanied by certain histological\nmodifications, such as the development of mutable connective tissues and\nskeletal elements that fused to ossicles and provided shape stabilization in\nthe form of a calcareous skeleton in the tissues of the body wall. The\nresultant organism was an ancestral eleutherozoan echinoderm (Ur-Echinoderm).",
"arxiv_id": "q-bio/0505038",
"authors": [
"Michael Gudo"
],
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"title": "Hydromechanical considerations on the origin of the pentaradial body structure of echinoderms",
"url": "https://arxiv.org/abs/q-bio/0505038"
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