Hochberg, R.*; Litvaitis, M. K.: The Nervous and Muscular System of Dactylopodola baltica from a Phylogenetic Perspective

Attempts to infer gastrotrich phylogeny from morphological characters has revealed the family Dactylopodolidae to be the sister taxon to the rest of the Macrodasyida. Dactylopodola retains several plesiomorphic characteristics making the genus worthy of attention for further phylogenetic investigation. Here we report the results of research on two organ systems of D. baltica, the muscular and nervous system. Immunofluorescent localization of acetylated tubulin and serotonin revealed the orientation of both main nerve cords and small sensory fibers in the species. In several cases, the nerves of D. baltica correspond in position to those of other macrodasyid taxa. Unique to D. baltica is the innervation of immunoreactive 5-HT neurons in the cerebral eyespots. In the muscular system, the arrangement of specific muscle sets is similar between D. baltica and other macrodasyidans: inner circular muscles, left- and right-handed helicoidal muscles, longitudinal muscles, and outer circular rings. The ventrolateral longitudinal muscles are uniquely arranged at the anterior and posterior portion of the body, as are their sites of insertion. It is proposed that the structure and orientation of the muscles and nerves reflect both local adaptation and phylogeny, and should provide a useful source for information on gastrotrich evolution.