Fig. 3 Expression of myosin II heavy chain (Dro-mhc_c1) and immunofluorescence staining in Dreissena rostriformis trochophore larvae. Anterior is up. Arrowheads indicate the stomodaeum, sf marks the shell field, dotted line outlines the region of the prototroch (pt). Scale bar equals 20 µm. Brightfield images (a, b) of the gene expression and confocal images (c, d) with F-actin (red), cilia (green; pt: prototroch; tt: telotroch), and cell nuclei staining (cyan). a Dro-mhc_c1 expression is first present in the anterior mesoderm. b Anterior mesodermal expression in dorsal view. c First F-actinpositive domain in the mesoderm below the shell field in the dorso-median region. d Slightly further developed trochophore larva showing two developing myofilaments in the median region. A, anterior; D, dorsal; P, posterior; V, ventral

Published as part of Schulreich, Stephan M., Salamanca-Díaz Andreas Wanninger, David A., Zieger, Elisabeth & Calcino, Andrew D., 2022, A mosaic of conserved and novel modes of gene expression and morphogenesis in mesoderm and muscle formation of a larval bivalve, pp. 893-913 in Organisms Diversity & Evolution 22 (4) on page 899, DOI: 10.1007/s13127-022-00569-5, http://zenodo.org/record/13167565