H. glycines body wall muscle undergoes ultrastructural changes during development.

Transverse TEM sections of body wall muscle in the midbody of H. glycines (left) and with pseudocolor overlay (right). (A) Mobile J2 H. glycines have intact muscle separated from the cuticle by a thin layer of epidermis. (B) Sedentary J3 muscle shows signs of atrophy including fewer thick and thin filaments and a thickening of epidermis. (C) J4 male muscle comprise distinct sarcomeres, but with reduced numbers of thick filaments and an epidermal thickness similar to J3s. (D) J4 females undergo further atrophy of sarcomeres and increased thickening of the epidermis beyond that seen in J3s. (E) The muscles of adult males are similar in orientation and size to J2 muscle. Scale bar, 1 μm.