Hochberg, R.: Function and systematic distribution of helicoidal muscles in Gastrotricha

Studies on the muscular system of gastrotrichs revealed the presence of muscles in a new orientation, that of left- and right-handed helices around the digestive tract. These helicoidal muscles are found on the pharynx and intestine of numerous species in both orders, Chaetonotida and Macrodasyida. In many cases, the helices surround both circular and longitudinal muscle bands. The number of helices is a function of ontogeny, and their position along the alimentary canal may be family-specific. To date, helicoidal muscles have been found in the following families: Chaetonotidae, Dactylopodolidae, Macrodasyidae, Thaumastodermatidae, Turbanellidae, and Xenotrichulidae. The precise function of these muscles remains to be determined, but we hypothesize that they play two roles: antagonize dilations of the pharynx and intestine during feeding and contribute to shape change in the body during ciliary locomotion. Based on their wide systematic distribution, these muscles are likely to be part of the ground pattern of the Gastrotricha.