Notes on the Facelinacea. II: On the systematic position of Hervia serrata Baba, 1949 and Favorinus horridus Macnae, 1954 (Mollusca Nudibranchia)

The eolids described under the names Hervia serrata BABA, 1949 and Favorinus horridus MACNAE, 1954, which were recently ascribed to other facelinid genera, such as Godiva (cf. MACNAE, 1954) and Dondice (cf. MARCUS, 1958), because of misconceptions on the taxonomic value of distinctive peculiarities in the Facelinacea, require a proper generic designation according to the author. Therefore the new genera Babaiella and Phyllodesmiopsis were constituted with H. serrata and F. horridus as type species. The distinguishing serrate teeth and other significant features exclude both genera from the Facelinacea and indicate a closer relationship with Phyllodesmium, a relatively abundant but very imperfectly known form, which was included among the aeolidiellids by BERGH (1892) upon the basis of an apparent resemblance of the radular teeth, which character, however, is considered to be the result of a remarkable parallelism due to the anthozoarian diet. The radula of the phyllodesmids is clearly different from the radular shapes of both the facelinids and aeolidiellids. From the former group it differs in having serrations (not denticles) which display a high degree of divergence from the axis of the median cusp. Even on external characters the phyllodesmids are already unmistakably characterized and cannot be confused with other eolids. There are thus substantial reasons for believing that the Phyllodesmiacea form a characteristic and close group which must be separated from both the Facelinacea and the Aeolidiacea, and their degree of specialization parallels the stage attained by the most specialized aeolidiellids. Our imperfect knowledge of this group does not yet allow further comparative studies; detailed anatomical and histological accounts will be necessary before our point of view can be placed on a more sure scientific basis. The phyllodesmids appear to belong exclusively to the Indo-Pacific region and a good number of new forms can be expected, because they are mimetic animals and little or no extensive collecting has been made on the most promising coasts until recently.