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Related Concept Videos

Gastrulation01:56

Gastrulation

Gastrulation establishes the three primary tissues of an embryo: the ectoderm, mesoderm, and endoderm. This developmental process relies on a series of intricate cellular movements, which in humans transforms a flat, “bilaminar disc” composed of two cell sheets into a three-tiered structure. In the resulting embryo, the endoderm serves as the bottom layer, and stacked directly above it is the intermediate mesoderm, and then the uppermost ectoderm. Respectively, these tissue strata will form...
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Updated: Jun 11, 2026

Three and Four-Dimensional Visualization and Analysis Approaches to Study Vertebrate Axial Elongation and Segmentation
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Three and Four-Dimensional Visualization and Analysis Approaches to Study Vertebrate Axial Elongation and Segmentation

Published on: February 28, 2021

Is the vertebrate head segmented?-evolutionary and developmental considerations.

Shigeru Kuratani1

  • 1Laboratory for Evolutionary Morphology, Center for Developmental Biology, RIKEN, 2-2-3 Minatojima-minami, Chuo, Kobe, Hyogo 650-0047, Japan.

Integrative and Comparative Biology
|July 8, 2010
PubMed
Summary
This summary is machine-generated.

The lamprey, a basal vertebrate, lacks segmental head mesoderm, challenging traditional vertebrate segmentation theories. This finding suggests the vertebrate head

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Area of Science:

  • Developmental biology
  • Evolutionary biology
  • Comparative embryology

Background:

  • Basal vertebrates like lampreys were expected to display segmental head mesoderm due to their phylogenetic position.
  • Previous assumptions suggested conserved segmentation patterns across vertebrates, including the head.

Purpose of the Study:

  • To investigate the presence or absence of segmental head mesoderm in lamprey embryos.
  • To re-evaluate classical theories of vertebrate segmentation in light of new findings.

Main Methods:

  • Comparative embryological analysis of lamprey embryos.
  • Examination of head mesoderm development and associated structures.
  • Review of existing literature on vertebrate segmentation.

Main Results:

  • Lamprey embryos lack somite-like segments in their head mesoderm.
  • Coelomic head cavities, prominent in some vertebrates, are not universal.
  • Vertebrate head mesoderm is secondarily regionalized, not primarily segmented.

Conclusions:

  • The vertebrate head lacks segmental generative constraints in its mesoderm.
  • Classical segmental theories equating the vertebrate head with amphioxus are refuted.
  • Lamprey findings necessitate a revised understanding of vertebrate head evolution and segmentation.