phenotype affects entity striated muscle myosin thick filament M line absent WBPhenotype:0000783 C_elegans_phenotype_ontology Animals lack the planar structure within the muscle sarcomere which lies midway within the thick filament (A) band, attaching to the plasma membrane at its base and running up towards the inward surface of the myofilament lattice, compared to control animals (Wormatlas). M line variant