Stage 1

Developmental timeline and staging designations for Smed embryogenesis. Timeline: days (d) post egg capsule deposition at 20˚C. Gray bars indicate time windows for RNA-Sequencing samples. Double headed arrows: time windows for Stages (S) S1-S8.


The Planarian Anatomoy Ontology (PLANA) is a collection of terms curated from the literature and other organism anatomy ontologies to describe anatomical features, life cycle stages and developmental processes in the regenerative flatworm Schmidtea mediterranea. The latest version of the PLANA Ontology is available through the Open Biological and Biomedical Ontology Foundry (OBO) . PLANA Ontology terms are searchable at the EMBL-EBI Ontology Lookup Service (OLS) and the PLANA Ontology Terms Page.

Below, the Overview Section is populated with infomration from the OLS.

Additional experimental information related to PLANA Ontology terms can be found in the Additional Term Information Section.

    ▻ Planarian Anatomy Ontology Term Overview

    ▻ Additional Term Information

      ▻ Description

      ▻ Figures

    Planarian Anatomy Ontology Term Overview


      Stage 1


      D0-D2. Zygote and dispersed blastomere cleavage in a yolk syncytium. Days 0-2 post-egg capsule deposition at 20˚C.



    TERM ID:



      Stage 1 "is a" embryo

      zygote "is a" Stage 1

      zygote, blastomere compartment, syncytial yolk cell, embryonic cleavage and blastomere "is a" Stage 1

      zygote, blastomere compartment, syncytial yolk cell, embryonic cleavage, blastomere, blastomere compartment, zygote, syncytial yolk cell, embryonic cleavage and blastomere "is a" Stage 1

      zygote "is a" Stage 1


    Click on the '-' and '+' to collapse and expand term 'is a' relationships.

    Planarian Anatomy Ontology


    Dynamically explore this term by selecting additional relationships to display ( checkboxes on the right ) and by expanding nodes by double clicking on a node. Single click on a node to display the definition below.


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    Additional Term Information

    All experimental data displayed here is from Davies et. al., 2017, Smed Embryogenesis Molecular Staging Resource


    Zygote(s) and yolk cells are packaged into egg capsules laid by the parent. The single cell stage can be visualized in histological cross-sections: spherical zygotes, ~ 25-30 µm in diameter, are surrounded by a halo of yolk cells reminiscent of the corona radiata. During early cleavage divisions blastomeres cycle asynchronously, without retaining direct cell-cell contacts, within a yolk syncytium. Embryos are readily apparent in histologically stained sections but may be difficult to locate in live, unstained specimens.


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    Figure 1 - figure supplement 1: Histological cross-sections of Stage 1 embryos. A-D: Four independent examples of the single cell stage (S1), either metaphase II arrested oocytes or zygotes, in paraffin embedded, hematoxylin and eosin stained sectioned egg capsules fixed at 1-2 days post egg capsule deposition (20˚C). The entire capsule is shown in D. Black arrowheads: metaphase II arrested oocytes or zygotes, surrounded by a corona of yolk cells. Scale bars: 25 µm (A-C); 100 µm (D).



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