The Musculature of Testudinella patina (Rotifera: Flosculariacea), Revealed with CLSM

Abstract

The musculature of Testudinella patina was visualized using phalloidin-linked fluorescent dye by confocal laser scanning microscopy. The conspicuous broad retractors appear to be made up of five separate fibers, of which three anchor in the neck region whereas two extend into the corona. Besides the broad retractors, a total of five paired longitudinal retractors are present and all of them extend into the corona. Incomplete circular muscles are found in groups in the neck region and in the medial and posterior parts of the trunk. The foot musculature comprises eight thin ventral foot muscles and six thicker dorsal foot muscles that all extend from the foot basis to the distal part of the foot. At the basis of the foot, each of the dorsal foot muscles anchors on a smaller, S-shaped subterminal foot muscle. The foot musculature furthermore comprises one pair of paraterminal foot muscles that each anchors basally on a subterminal foot muscle, extends into the most proximal part of the foot and attaches on one of the dorsal foot muscles. The visceral musculature is composed of extremely delicate fibers and is restricted to an area around and posterior to the foot opening. The presence of incomplete circular muscles supports that these muscles are a basal trait for Rotifera, whereas the morphology of the broad retractors and foot muscles is much more specialized and may be autapomorphic for Testudinella or alternatively for this genus and its closest relatives. The present results stress that revealing muscles by staining may produce new information from even well-investigated species, and that this information may contribute to a better understanding of functional as well as phylogenetic aspects of rotifer biology.