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Figure 10 | Frontiers in Zoology

Figure 10

From: Myogenesis of Malacostraca – the “egg-nauplius” concept revisited

Figure 10

Phylogram of hypothesized evolutionary history of myogenesis. Phylogenetic relationships refer to [19, 51]. Anostraca are used as an outgroup without implying that they are sister group to Eumalacostraca or Malacostraca. Dendrobranchiata are included, represented by Sicyonia ingentis, [54]. Evolutionary changes of myogenesis are shown as inferred from comparison of the simplified myogenic sequences shown in Figure 9. Only extrinsic muscle precursors and the posterior pioneer muscle strand are considered and the three nauplius segments are combined to one category. The features plotted on the tree are: egg-nauplius, advanced embryonic stage, nauplius larva, zoea-like larva, early onset of myogenesis in embryonic naupliar segments, early onset of myogenesis in embryonic naupliar segments and the first maxilla segment, lack of advanced myogenesis in nauplius segments relative to postnaupliar segments. The features are shown as small icons. Loss of either larval form is indicated by a ‘ghost’-icon. Presence of a posterior pioneer longitudinal muscle strand (lmp-post) is coded to the branches (pink). Absence of lmp-post is given in black. A free swimming nauplius larva is part of the ground pattern and has been lost three times independently in the Stomatopoda, Pleocyemata and Peracarida. In clades which possess lmp-post, zoea-like larvae are commonly found, indicating that both features are dependent upon each other. Loss of a zoea-like larva is clearly derived in N. heteropoda and P. fallax f. virginalis. Therefore a zoea-like larva is shown for the last common ancestor. Abbreviations: A1, A2, Md, Mx1 Body segments bearing respective appendages.

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