English: Frilled protractor muscles can only be found in sea urchin species of the families Toxopneustidae, Echinometridae, and Strongylocentrotidae (K–P). See Fig. 6 for a phylogeny of the Echinoidea, while Table 3 lists character distribution in all 49 echinacean species analyzed in this study. (A) Stomopneustes variolaris (Stomopneustidae). (B) Arbacia dufresnii (Arbaciidae). (C) Parasalenia gratiosa (Parasaleniidae). (D) Temnopleurus toreumaticus and (E) Pseudechinus magellanicus (Temnopleuridae). (F) Trigonocidaris albida (Trigonocidaridae). (G) Polyechinus agulhensis and (H) Sterechinus neumayeri (Echinidae). (I) Parechinus angulosus and (J) Psammechinus microtuberculatus (Parechinidae). (K) Toxopneustes pileolus and (L) Sphaerechinus granularis (Toxopneustidae). (M) Echinometra lucunter and (N) Heterocentrotus mammilatus (Echinometridae). (O) Pseudocentrotus depressus and (P) Hemicentrotus pulcherrimus (Strongylocentrotidae). (A–E), (G–K), and (N–P) based on MRI datasets with 50×50×200 µm resolution. (F) based on a MRI dataset with 32 µm isotropic voxel resolution. (L, M) based on MRI datasets with 78×78×500 µm resolution. lo = lobe.