Binary fission in Trichoplax is orthogonal to the subsequent division plane

https://doi.org/10.1016/j.mod.2020.103608Get rights and content
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Highlights

  • Binary fission in Trichoplax follows an orthogonal axis relative to previous fission

  • During binary fission, a longitudinal symmetry axis manifested in the longitudinal ridge and pulling direction of the daughter individuals

  • We postulate that placozoans have an ideal circular body and a cryptic cylindrical symmetry

Abstract

Asexual reproduction in Trichoplax occurs mainly by binary fission and occasionally by the budding of epithelial spheres called “swarmers”. The process that leads to binary fission and the mechanisms involved in this segregation are practically unknown. Trichoplax lacks a defined shape, presenting a constantly changing outline due to its continuous movements and body contractions. For this reason, and due to the absence of anatomical references, it has been classified as an asymmetric organism. Here, we report that a transient wound is formed in the marginal epithelium of the two new individuals produced by binary fission. By tracking the location of this epithelial wound, we can determine that successive dichotomous divisions are orthogonal to the previous division. We also found that LiCl paralyzes the cilia beating movement and body contractions and causes the placozoans to become circular in shape. This effect, as well as a stereotypic body folding behavior observed in detached placozoans and cell labeling experiments of the upper epithelium, indicate a cylindrical body symmetry for Placozoa.

Keywords

Trichoplax
Symmetry
Binary fission
Placozoa

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