Figure 2.

Myoanatomy of Late-Stage Larvae of the Polyplacophoran Leptochiton asellus and the Neomeniomorph Wirenia argentea

Major homologous muscle units are indicated by shared color code. Scale bars represent 20 μm. The dorsoventral muscles (violet) are easily identified in (E) and (F) since they overlie the ventrolateral muscles (green) due to their more dorsally situated insertion sites. They intercross in the region of the ventromedian muscle (orange) and are depicted as dots to indicate their major dorsal insertion sites in (C) and (D). (A), (B), (E), (F), (I), and (J) are 3D reconstructions based on confocal microscopy data sets. (C), (D), (G), (H), (K), and (L) are schematic representations. For better visualization of individual muscle systems, only ventral or dorsal halves of larvae with section plane in the region of the enrolling muscle are shown in (A)–(H).

(A) Leptochiton asellus, dorsal muscle systems seen from ventral.

(B) Wirenia argentea, dorsal muscle systems seen from ventral.

(C) Leptochiton asellus, dorsal muscle systems seen from ventral.

(D) Wirenia argentea, dorsal muscle systems seen from ventral.

(E) Leptochiton asellus, ventral muscle systems seen from dorsal.

(F) Wirenia argentea, ventral muscle systems seen from dorsal.

(G) Leptochiton asellus, ventral muscle systems seen from dorsal.

(H) Wirenia argentea, ventral muscle systems seen from dorsal.

(I) Leptochiton asellus, ventrolateral right view. Note that the rudimentary body wall musculature is restricted to the anterior body region.

(J) Wirenia argentea, ventrolateral right view.

(K) Leptochiton asellus, cross-section with all muscle systems identified herein. Note that transversal muscles (pink) are found in the dorsal and ventral region. It remains unclear whether or not these have evolved from body wall ring muscles [24].

(L) Wirenia argentea, cross-section with all muscle systems identified herein.