![]() ![]() Origins of bilateral symmetry: Hox and Dpp expression in a sea anemone. Genomics and development of Nematostella vectensis and other anthozoans. Unexpected complexity of the Wnt gene family in a sea anemone. On growth and form: a Cartesian coordinate system of Wnt and BMP signaling specifies bilaterian body axes. Selective heart rate reduction improves metabolic syndrome-related left ventricular diastolic dysfunction. Did internal transport, rather than directed locomotion, favor the evolution of bilateral symmetry in animals? BioEssays 27, 1174–1180 (2005). On the origin of metameric segmentation and some other morphological questions. The Invertebrates: Protozoa through Ctenophora Vol. Characterization of morphological and cellular events underlying oral regeneration in the sea anemone, Nematostella vectensis. The aboral pore of hydra: evidence that the digestive tract of hydra is a tube not a sac. Different strategies for midline formation in bilaterians. The Invertebrates: Platyhelminthes and Rhynchocoela. From nerve net to nerve ring, nerve cord and brain-evolution of the nervous system. The presence of a functionally tripartite through-gut in Ctenophora has implications for metazoan character trait evolution. Evolution of deuterostomy - and origin of the chordates. ![]() Larval ciliary bands and metazoan phylogeny. A developmental perspective: changes in the position of the blastopore during bilaterian evolution. Deuterostomic development in the protostome Priapulus caudatus. Acoel development supports a simple planula-like urbilaterian. Dorsal or ventral: similarities in fate maps and gastrulation patterns in annelids, arthropods and chordates. Amphioxus mouth after dorso-ventral inversion. The study of Priapulus caudatus reveals conserved molecular patterning underlying different gut morphogenesis in the Ecdysozoa. Evolution of the bilaterian larval foregut. Inversion of dorsoventral axis? Nature 371, 26 (1994). Phylogenomic insights into animal evolution. Animal phylogeny and its evolutionary implications. Teil 1: Einzeller und Wirbellose (eds Westheide, W. Invertebrates 3rd edn (Sinauer, Sunderland, MA, 2016). Animal Evolution: Interrelationships of the Living Phyla 3rd edn, (Oxford Univ. Die Gastraea-Theorie, die phylogenetische Classification des Thierreichs und die Homologie der Keimblätter. Generelle Morphologie der Organismen (Georg Reimer, Berlin, 1866). ![]() Die systematische Einteilung des Tierreichs. We discuss remaining difficulties, and outline directions for future research. Available evidence indicates that stem bilaterians had a slit-like gastric opening that was partially closed in subsequent evolution, leaving open the anus and most likely also the mouth, which would favour amphistomy. Here we review comparative data on the identity and fate of blastoporal tissue, investigate how the formation of the through-gut relates to the major body axes, and discuss to what extent evolutionary scenarios are consistent with these data. Did the single gastric opening evolve into a mouth, with the anus forming elsewhere in the body (protostomy), or did it evolve into an anus, with the mouth forming elsewhere (deuterostomy), or did it evolve into both mouth and anus (amphistomy)? These questions are addressed by the comparison of developmental fates of the blastopore, the opening of the embryonic gut, in diverse animals that live today. However, there is no consensus on how this happened. It is widely held that the bilaterian tubular gut with mouth and anus evolved from a simple gut with one major gastric opening. ![]()
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