Fig. 2.

(A) Schematic representation of several molecules in vertebrate skeletal sarcomeres. Contraction occurs in response to calcium using troponin–tropomyosin regulatory mechanisms (Schmidt-Rhaesa 2007; Marieb and Hoehn 2015). (B) Schematic of estimated muscle protein gene trees (supplementary fig. S2A–G, Supplementary Material online). Black bars with lower case letters indicate gene duplication events. Upper case letters in clade names indicate inferred expressions of ancestral genes (A, adult; B, body-wall muscle; C, cytoplasm; C/M, cytoplasm or muscle; H, heart; Lmod, leiomodin; M, muscle; N, notochord muscle; P, paraxial muscle; Tmod, tropomodulin; TPML, tropomyosin-like). Triangles indicate gene grouping in which monophyly is supported (closed) or not (open).