On the central nervous system of Smeagolidae and Rhodopidae, two families questionably allied with the Gymnomorpha (Gastropoda: Euthyneura)

Abstract

The central nervous systems (CNS) of Smeagol manneringi Climo, 1980 (Smeagolidae), of Rhodope veranü Kölliker, 1847, and of Rhodope transtrosa Salvini‐Plawén, 1989 are redescribed in detail. The smeagolid CNS exhibits diagnostic pulmonate characters (procerebrum, cerebral gland, dorsal bodies). Sharing a distinctly structured abdominal ganglion and other peculiarities, the Smeagolidae are closely related to the Onchidüdae, and both families are united as Onchidioidea. The consequences of this close relationship for the origin and evolution of the Gymnomorpha are discussed and the value of the pulmonate CNS for phylogenetics is reconsidered. On the basis of neural characters, which are correlated with the mode of breathing organs, the Pulmonata are divided into Basommatophora, Systellommatophora (Otinidae and Gymnomorpha) and Eupulmonata (ord. nov.: Trimusculidae, Ellobüdae, Stylommatophora).In contrast, the CNSs of the rhodopid species lack the pulmonate attributes, but show diagnostic opisthobranch characters such as a rhinophoral nerve. Accordingly, the Rhodopidae are excluded from the Pulmonata and are classified as a separate order Rhodopemorpha among the Opisthobranchia.