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Fig. 2 | Frontiers in Zoology

Fig. 2

From: From egg to “no-body”: an overview and revision of developmental pathways in the ancient arthropod lineage Pycnogonida

Fig. 2

Embryonic development of Pycnogonida. a-c Pycnogonum litorale (Pycnogonidae), representing ‘small egg’ pycnogonids. a Four cell stage (Sytox nucleic acid staining). The blastomeres are of equal size. Asterisks mark cell nuclei, arrows indicate two brightly stained granules. b Initiation of gastrulation (Sytox nucleic acid staining). Note the immigration of the large bottle-shaped cell that is still attached to the embryo’s surface (arrowhead). c Embryonic morphogenesis (SEM). In the shown developmental stage, the proboscis, cheliphores and palpal and ovigeral larval limbs of the prospective protonymphon larva are recognizable. a&b modified from [10] and reproduced with permission of Springer; c modified from [11] and reproduced with permission of John Wiley and Sons. d-f Meridionale sp. (Callipallenidae), representing ‘large egg’ pycnogonids. d Early germ band stage (SEM). One embryonic hemisphere is covered by the densely packed small germ band cells, whereas the other hemisphere features few large yolk-rich cells (arrowheads). Asterisk indicates a damaged region. e Slightly later germ band stage (Sytox nucleic acid staining). Note stomodeum (arrow) in a far anterior position, being posteriorly followed by the cheliphore limb buds. Scattered nuclei around the germ band illustrate successive overgrowing of the large yolk-rich cells of the other embryonic hemisphere. f Late embryonic morphogenesis (SEM). Note that Meridionale sp. hatches as an advanced postlarva and develops walking leg pairs 1 and 2 before hatching. d&f modified from [12] and reproduced with permission of Springer

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