Anatomy of neuronal and muscular systems in two species of Loxosomatidae (Entoprocta)

Fuchs, J., M. Bright & A. Wanninger

1 Department of Marine Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria; 2 Department of Cell Biology and Comparative Zoology, Biological Institute, Universitetsparken 15, University of Copenhagen, 2100 Copenhagen Ø, Denmark

Correspondence
Judith Fuchs
E-mail: judith_fuechsin@yahoo.de

Abstract

Little detailed information exists on the anatomy of the nervous system and the musculature of most species of Entoprocta. Herein, we describe the distribution of the neurotransmitters serotonin and FMRFamide as well as the myo-anatomy of adults and asexually produced budding stages of the solitary entoproct species Loxosomella vivipara and Loxosomella parguerensis. Data are revealed by means of immunocytochemistry and epifluorescence as well as confocal laser scanning microscopy. The development of the FMRFamidergic and serotonergic nervous system starts in early budding stages. FMRFamide is distributed throughout the major body regions, the calyx, stalk, and foot. It is present in the cerebral ganglion, the ventral nerve cords that innervate two pairs of heel ganglia in the foot, the aboral nerve cords, the lateral nerves, the stomach nerves, the tentacle nerves, as well as further distinct nerves in the calyx. Serotonin has a more restricted distribution. It is found in nerves in the calyx. Both neurotransmitters are distributed in the cerebral ganglion, the ventral nerve cords, and tentacle nerves. Some differences in the distribution of both neurotransmitters are observed between L. vivipara and L. parguerensis and are most obvious in the differing number of serotonergic cells belonging to the ventral nerve cords. Nerves arising from the cerebral ganglion and running in ventral direction have not been described for Entoprocta before and the possibility of homology of these to the ventral nerve cords of other Protostomia is discussed. The body musculature of the two loxosomatid species comprises longitudinal and diagonal muscles in the foot, stalk, and calyx. Several circular muscles are observed in the calyx, and a fine layer of ring musculature surrounds the stalk and parts of the foot and the calyx. In addition to the congruent details regarding the myo-anatomy of both species, species-specific muscle structures could be revealed. The comparison of our data with recent findings on two species of solitary Loxosoma indicates that longitudinal body muscles, paired atrial ring muscles, main and two pairs of inner tentacle muscles, esophagal and rectal ring muscles, as well as intestinal and anal sphincters could have been part of the ancestral entoproct muscle bauplan. Overall, this study reveals complex neuronal as well as muscular systems in Entoprocta and demonstrates the usefulness of both features for phylogenetic inferences.