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Fig. 7 | BMC Evolutionary Biology

Fig. 7

From: From complex to simple: myogenesis in an aplacophoran mollusk reveals key traits in aculiferan evolution

Fig. 7

Reconstruction of the larval and adult myogenic body plan of the last common aculiferan ancestor. Apical is up in all larval schemes. Anterior is to the left in schemes of juveniles as well as adults. Schematic illustrations indicate ontogeny (fine arrows) from late larval until the adult stage. Evolutionary transitions are indicated by massive arrows. Because it is not determinable whether the larval stages of the last common ancestor exhibited a neomeniomorph-like seven-fold seriality or a polyplacophoran-like multiple seriality of inner dorsoventral musculature, the additional muscles are stippled. Referring to this, the (R) indicates a possible numeric reduction of inner dorsoventral musculature during neomeniomorph evolution and, as alternative, the (M) indicates a possible multiplication of inner dorsoventral musculature during polyplacophoran evolution. All stages are shown translucent in lateral view from the left with an additional scheme of a median cross section below. Serial arrangement of shell plates and the corresponding dorsoventral musculature is indicated by numbering of the depicted structures. Note the shared seven-fold seriality in juveniles of Polyplacophora and Neomeniomorpha as represented by dorsoventral muscles and shell plates. For better visualization, the outer dorsoventral musculature is exclusively drawn in cross section schemes, and helicoidal musculature is not depicted. Homologous muscular elements are indicated by color code corresponding to previous figures: yellow, prototroch muscle ring; dark blue, enrolling muscle; green, ventrolateral muscle; violet, inner dorsoventral musculature; light violet, outer dorsoventral musculature; cyan, ring musculature/transversal musculature; red, rectus muscle; orange, ventromedian muscle

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