The “Spiralia” represent one of the three major clades of bilaterian metazoans. Though
members of this clade exhibit tremendous diversity in terms of their larval and adult body …

Sipuncula is an ancient clade of unsegmented marine worms that develop through a
conserved pattern of unequal quartet spiral cleavage. They exhibit putative character …

Gastrulation is a critical stage of metazoan development during which endodermal and
mesodermal tissues are internalized, and morphogenesis transforms the early embryo into …

Recent progress in reconstructing animal relationships enables us to draw a better picture of
the evolution of important characters such as organ systems and developmental processes …

Flatworm embryology has attracted attention since the early beginnings of comparative
evolutionary biology. Considered for a long time the most basal bilaterians, the …

At least five animal phyla exhibit spiralian development, which is characterized by striking
similarities in the geometry of the early cleavage pattern and the fate map of the blastula …

The spiralian developmental program is a highly conserved mode of early development that
is characterized by regularities in cleavage pattern, fate map, and larval morphology. It is …

Progress in resolving the phylogenetic relationships among animals and the expansion of
molecular developmental studies to a broader variety of organisms has provided important …

It is clear that the spiralian developmental program represents a highly flexible platform for
the generation of diverse larval and adult body plans. The widespread occurrence of this …

Background Planktonic life history stages of spiralians share some muscular, nervous and
ciliary system characters in common. The distribution of these characters is patchy and can …