Rana evolucija Metazoa
The first modern definition of animals goes back to Haeckel who introduced the name Metazoa for a holophyletic group descended from gastraea. Since then, many have passionately discussed the phylogeny and evolution of metazoans. In this paper, historical context for some phylogenetic and evolutionary ideas being discussed or accepted today is given, as well as temporal context for the early evolution of Metazoa dealing with the phenomenon of Cambrian “explosion“. A gallery of portraits of four non-bilaterian phyla is given to understand the ideas about origin of genes and structures in early animal evolution, with emphasis on some misconceptions and most recent findings. It is universally accepted that choanoflagellates are sister group of metazoans, and these and other unicellular relatives of metazoans are important for understanding the origin of animal multicellularity. Although the main phylogenetic relationships of Bilateria are well suported, there is no general agreement on the relationships between non-bilaterian phyla, with Ctenophora and Porifera both proposed to be sister groups to all other metazoans, making it even more difficult to understand the origin of, for example, gastrulation, nervous system and ANTP genes. Discussion of other important topics, like the very origin of metazoans from their unicellular (or colonial) ancestors and the origin of through-gut in Eubilateria is also given. The list of proposed animal apomorphies is given. It is concluded that molecular biology is very important, but not omnipotent tool for understanding animal evolution, and that morphology, the diversity of which we want to explain, deserves equal interest.