Distribution of catecholamine-containing,serotonin-like and neuropeptide FMRFamide-like immunoreactive neurons and processes in the nervous system of the actinotroch larva ofPhoronis muelleri (Phoronida)

Summary Glyoxylic-acid-induced fluorescence of catecholamines and antibodies against serotonin and FMRFamide were used to study the distribution of putative neurotransmitters in the actinotroch larva ofPhoronis muelleri Selys-Longchamps, 1903. Catecholamines occur in the neuropile of the apical ganglion, in the longitudinal median epistome nerves, in the epistome marginal nerves, and in the nerve along the bases of the tentacles. The tentacles have laterofrontal and latero-abfrontal bundles of processes that form two minor nerves along the lateral ciliary band of the tentacles, and a medio-frontal bundle of processes. Monopolar cells are located on the ventro-lateral part of the mesosome. Processes are located along the posterior ciliary band and as a reticulum in the epidermis. Serotonin-like immunoreactive cells and processes are located in the apical ganglion, in the longitudinal median epistome nerves, and as a dorsal and ventral pair of bundles along the tentacle bases. Processes from the latter extend into the tentacles as the medioabfrontal processes. The latero-abfrontal processes form a minor nerve along the ciliary band. The dorsal bundles forms the major nerve ring along the tentacles and processes extend from it to the metasome. Processes are located along the posterior ciliary band. FMRFamide-like immunoreactive cells and processes are found in the apical ganglion, in the longitudinal median epistome nerves and as a pair of lateral epistome processes projecting towards the ring of tentacles. In the tentacles, a pair of latero-frontal processes are found; these form a minor nerve along the ciliary band. A band of cells can be seen along the tentacle ring.