Neuronal components of the superior and inferior tentacles in the terrestrial slug, Limax marginatus

To identify the types of neurons and to infer the patterns of connectivity in slug tentacles, we stained the neurons in the superior and inferior tentacles in the terrestrial slug, Limax marginatus, by backfilling of the tentacular nerves with Lucifer yellow. Four types of stained neurons, '(1) sensory neurons', '(2) gamma cells', '(3) ganglion cells', '(4) lateral cells', were identified both in the superior and inferior tentacles. Three subtypes of the sensory neurons, '(1a) round sensory neurons', '(1b) spindle-shaped sensory neurons', and '(1c) small sensory neurons', were found in the digits. The gamma cells and the ganglion cells were interneurons. Three subtypes of gamma cells, '(2a) round monopolar gamma cells', '(2b) round bipolar gamma cells', and '(2c) large gamma cells', were present in the digits. The ganglion cells were composed of '(3a) monopolar ganglion cells', '(3b) bipolar ganglion cells', and '(3c) elongated ganglion cells'. The monopolar and bipolar types were located both in the tentacular ganglia and digits, whereas the elongated type was present only in the tentacular ganglia. The lateral cells, whose function is unknown, were found in the dermo-muscular sheaths of the tentacles. Our study provides the first description of the neuronal map of inferior tentacles in gastropods. The results showed no differences in the morphological features of stained neurons between the superior and inferior tentacles in L. marginatus.