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Early embryogenesis of planaria: a cryptic larva feeding on maternal resources

Abstract

The early planarian embryo presents a complete ciliated epidermis and a pharynx and feeds on maternal yolk cells. In this paper, we report on all the elements involved in the formation of such an autonomous embryo, which we name cryptic larva. First, we provide a description of the spherical and fusiform yolk cells and their relationship with the blastomeres, from the laying of the egg capsule up to their final fate in mid embryonic stages. Then, we describe the early cleavage and the subsequent development of the tissues of the cryptic larva, namely, the primary epidermis, the embryonic pharynx, and a new cell type, the star cells. Finally, we discuss the possibility that the cryptic larva either constitutes a vestigial larva or, more likely, is the evolutionary result of the competition between multiple embryos for the limited and shared maternal resources in the egg capsule.

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Acknowledgements

The authors wish to express their gratitude to Núria Cortadellas and Almudena Fernández from the Serveis Científico-Técnics UB for their exquisite professional expertise in electron microscopy, to Juani Fernandez-Rodriguez for sharing her expertise in generating and hybridizing myoD probes, and also to Cati Lee for laboratory assistance in sequencing and synthesizing the probes. The authors are deeply thankful for extensive and encouraging comments from the anonymous reviewers. AC was supported by an FPU fellowship from the MEC, Spain. This work was supported by grants NIH NS29367 and NSF to IBN-0110718 to VH and BFU2004-05015 from the PNIC-DIT 2004-07 by the MEC, Spain to RR. Many thanks to Lukas Schärer and the Institute of Zoology in Innsbruck for extremely helpful discussions.

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Correspondence to Albert Cardona.

Additional information

Communicated by D.A. Weisblat

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Cardona, A., Hartenstein, V. & Romero, R. Early embryogenesis of planaria: a cryptic larva feeding on maternal resources. Dev Genes Evol 216, 667–681 (2006). https://doi.org/10.1007/s00427-006-0094-3

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Keywords

  • Flatworm
  • Planaria
  • Embryogenesis
  • Larva
  • Competition