The puzzle of how complex nervous systems emerged remains unsolved. Comparative
studies of neurodevelopment in cnidarians and bilaterians suggest that this process began …

Deuterostomes are the major division of animal life which includes sea stars, acorn worms,
and humans, among a wide variety of ecologically and morphologically disparate taxa …

Background Invertebrate nervous systems are highly disparate between different taxa. This
is reflected in the terminology used to describe them, which is very rich and often confusing …

Background Planktonic ciliated larvae are characteristic for the life cycle of marine
invertebrates. Their most prominent feature is the apical organ harboring sensory cells and …

Summary Ambulacraria, comprising Hemichordata and Echinodermata [1], is closely related
to Chordata, making it integral to understanding chordate origins and polarizing chordate …

While some aspects of the phylogeny of the five living echinoderm classes are clear, the
position of the ophiuroids (brittlestars) relative to asteroids (starfish), echinoids (sea urchins) …

Hemichordates are an important group for investigating the evolution of bilaterian nervous
systems. As the closest chordate outgroup with a bilaterally symmetric adult body plan …

The ecologically significant shift in developmental strategy from planktotrophic (feeding) to
lecithotrophic (nonfeeding) development in the sea urchin genus Heliocidaris is one of the …

Ctenophores are non-bilaterian animals sharing with cnidarians and bilaterians the
presence of sensory receptors, nerve cells, and synapses, absent in placozoans and …

Highlights•The two signalling systems that pattern the bilaterian forebrain evolved on
opposite body sides.•These systems initially specified two spatially separate condensations …