Favorinidae Bergh, 1889

Family Favorinidae Bergh, 1889 , reinstated

( Figs 1, 2; Table 4)

Subfamily Favorininae Bergh 1889: 212 View in CoL .

Family Favorinidae ‘Bergh, 1890’: Odhner in Franc 1968: 886. Family Favorinidae : Thompson and Brown 1984: 154. Goodheart et al. 2018: 11.

Martynov et al. 2019: 109, 110.

Diagnosis: Body narrow. Notal edge completely reduced. Anterior cerata in distinct arches, posterior ceratal rows in arches and rows. Rhinophores with swellings or smooth. Anus cleioproctic. Masticatory edges of jaws moderately denticulated. Radula formula 0.1.0. Central teeth with reduced denticles, or denticles absent, cusp non-compressed. Distal and proximal receptaculum seminis. Vas deferens moderately long to short, prostate indistinct or distinct. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, not considerably widened, unarmed.

Genera included: Favorinus Gray, 1850 .

Remarks: The family Favorinidae , reinstated, is well characterized by the combination of central teeth of radula with predominantly reduced to completely absent denticles, rhinophores commonly with swellings instead of lamellae or papillae, and ark-shaped, anterior ceratal rows. Its distinctness was recognized by Bergh (1889) and further several taxonomists had considered that family as valid (e.g.Odhner in Franc 1968, Thompson and Brown 1984). Recently, the family Favorinidae has been recovered as valid in several analyses and it was shown that favorinids represent an ancestral group for the evolutionary formation of the highly aberrant pleistonic Glaucidae ( Goodheart et al. 2018, Martynov et al. 2019, Colin et al. 2024, present study; Figs 1, 2). However, in WoRMS (2024) this family is still considered, for some unclear reason, as ‘unaccepted’. Importantly, if Favorinidae Bergh, 1889 were synonymyzed with Facelinidae Bergh, 1889 , then it must be formally synonymyzed (see below) with its sister, again, the profoundly aberrant family Glaucidae Gray, 1827 . Furthermore, the family Glaucidae Gray, 1827 , which is drastically different from all taxa of the suborder Aeolidacea , was established on the same date with the ‘type’ for the entire Aeolidacea family Aeolidiidae Gray, 1827 . Thus, a cascade of unsubstantiated family-level synonymyzation will inevitably ruin any taxonomic structure within the suborder Aeolidacea . We, therefore, formally restore the family Favorinidae Bergh, 1889 , reinstated, and again reiterate that if one finely differentiated taxon vanishes due to lumping at any level—including genera and families—almost all other families (e.g. all families within the superfamily Aeolidioidea ) could also potentially be lumped into each other such that only one of two of the oldest families, Aeolidiidae Gray, 1827 or Glaucidae Gray, 1827 would be left. To avoid this highly inconsistent action, both from a morphological and a molecular perspective, finely differentiated taxa should be maintained to the maximal degree possible. In fact, more families, even within the restricted Facelinidae ( Martynov et al. 2019) , still need to be separated and restored in the future.