Morphological evidence for a morphogenetic field in gastropod mollusc eggs.

Eggs of the marine gastropod Crepidula fornicata examined by confocal imaging of FITC-lectin binding to the surface, and cryoscopic-SEM both reveal a surface architecture of linear structures organized around the animal-vegetal axis, which is spatially related to the anterior-posterior (a-p) axis of the subsequent embryo. A series of structures is also orientated with reference to specific micromere quartets formed during spiral cleavage. Thus, the surface architecture may provide a visible marker for a morphogenetic field which generates the a-p axis and organizes the cleavage pattern. Moreover, this architecture is co-extensive with that found on the vegetal, polar lobe-bearing region of eggs, as described by others, and which varies between gastropod taxa with varied types of body form. Confocal imaging reveals a distinct localization of F-actin to the architecture of the lobe region. However, the integrity of this F-actin is not responsible for the maintenance of the surface architecture. The significance of these findings to our understanding of the generation of diversity within the Gastropoda and general ontogenic mechanisms is discussed.