scholarly journals Haeckel's Gastraea Theory

1876 ◽  
Vol 10 (2) ◽  
pp. 73-75
Author(s):  
Alexander Agassiz
Keyword(s):  
Gastraea Theory

scholarly journals Origin of animal multicellularity: precursors, causes, consequences—the choanoflagellate/sponge transition, neurogenesis and the Cambrian explosion

2017 ◽  
Vol 372 (1713) ◽  
pp. 20150476 ◽  
Author(s):  
Thomas Cavalier-Smith
Keyword(s):  
Connective Tissue ◽  
Photosynthetic Bacteria ◽  
Cell Structure ◽  
Morphological Diversity ◽  
Cambrian Explosion ◽  
Feeding Modes ◽  
Selection For ◽  
Evo Devo ◽  
Gastraea Theory ◽  
Bacterial Food

Evolving multicellularity is easy, especially in phototrophs and osmotrophs whose multicells feed like unicells. Evolving animals was much harder and unique; probably only one pathway via benthic ‘zoophytes’ with pelagic ciliated larvae allowed trophic continuity from phagocytic protozoa to gut-endowed animals. Choanoflagellate protozoa produced sponges. Converting sponge flask cells mediating larval settling to synaptically controlled nematocysts arguably made Cnidaria. I replace Haeckel's gastraea theory by a sponge/coelenterate/bilaterian pathway: Placozoa, hydrozoan diploblasty and ctenophores were secondary; stem anthozoan developmental mutations arguably independently generated coelomate bilateria and ctenophores. I emphasize animal origin's conceptual aspects (selective, developmental) related to feeding modes, cell structure, phylogeny of related protozoa, sequence evidence, ecology and palaeontology. Epithelia and connective tissue could evolve only by compensating for dramatically lower feeding efficiency that differentiation into non-choanocytes entails. Consequentially, larger bodies enabled filtering more water for bacterial food and harbouring photosynthetic bacteria, together adding more food than cell differentiation sacrificed. A hypothetical presponge of sessile triploblastic sheets (connective tissue sandwiched between two choanocyte epithelia) evolved oogamy through selection for larger dispersive ciliated larvae to accelerate benthic trophic competence and overgrowing protozoan competitors. Extinct Vendozoa might be elaborations of this organismal grade with choanocyte-bearing epithelia, before poriferan water channels and cnidarian gut/nematocysts/synapses evolved. This article is part of the themed issue ‘Evo-devo in the genomics era, and the origins of morphological diversity’.

scholarly journals XLIII.—Remarks on the gastræa-theory

1884 ◽  
Vol 13 (77) ◽  
pp. 372-383
Author(s):  
G. Bütschli
Keyword(s):  
Gastraea Theory

scholarly journals The Biogenetic Law and the Gastraea Theory: From Ernst Haeckel´s Discoveries to Contemporary Views

2020 ◽  
Author(s):  
Georgy S. Levit ◽  
Uwe Hoßfeld ◽  
Benjamin Naumann ◽  
Paul Lukas ◽  
Lennart Olsson
Keyword(s):  
Common Ancestor ◽  
Present Situation ◽  
Cell Types ◽  
Molecular Data ◽  
Last Common Ancestor ◽  
Ernst Haeckel ◽  
Biogenetic Law ◽  
Glass Model ◽  
Further Development ◽  
Gastraea Theory

More than 150 years ago, in 1866, Ernst Haeckel published a book in two volumes called "Generelle Morphologie der Organismen" (General Morphology of Organisms) in the first volume of which he formulated his Biogenetic law, famously stating that ontogeny recapitulates phylogeny (Rieppel 2019). Here we describe Haeckel´s original idea as first formulated in the “Generelle Morphologie der Organismen” and later further developed in other publications until the present situation in which molecular data are used to test the "hour-glass model", which can be seen as a modern version of the biogenetic law. We also tell the story about his discovery, while travelling in Norway, of an unknown organism, Magosphaera planula, that was important in that it helped to precipitate his ideas into what was to become the Gastraea theory. We also follow the further development and reformulations of the Gastraea theory by other scientists, notably the Russian school (Levit, 2007). Ilya Metchnikov developed the Phagocytella hypothesis for the origin of metazoans based on studies of a colonial flagellate. Alexey Zakhvatin focused on deducing the ancestral life cycle and the cell types of the last common ancestor of all metazoans, and Mikhailov recently pursued this line of research further.

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