A longitudinal crosssection of an individual O. muscos using histolological staining. Olymbus CH2microscope under 4x magnification. Labelled boxes represent: a) primarymesentries b) tertiary mesentries c) Oral stoma d) Tentacle e) Sphincter musclef) endocoelic chambers g) mesentral retractor muscles (longitudinal musclefields) h) cluster of nematocysts i) actinopharynx j) mesentrial filaments k)verruca.