Trinchesiidae Nordsieck, 1972

Korshunova, Tatiana, Fletcher, Karin & Martynov, Alexander, 2025, The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case, Zoological Journal of the Linnean Society 204 (4) : -

publication ID	https://doi.org/10.1093/zoolinnean/zlaf057
publication LSID	lsid:zoobank.org:pub:D09886E-5D7C-40D1-B86A-118A3ADE5773
persistent identifier	https://treatment.plazi.org/id/03EF87FE-FF9A-FFFF-FF09-F9DCFAD5F946
treatment provided by	Plazi
scientific name	Trinchesiidae Nordsieck, 1972
status

Treatment

Family Trinchesiidae Nordsieck, 1972 View in CoL

( Figs 1, 2, 5A; Table 4)

Nordsieck, 1972: 5, 80.

Family Trinchesiidae View in CoL restored: Korshunova et al. 2017c: 9, 14, 17, 18.

Korshunova et al. 2017a: supplementary materials.

Diagnosis: Body commonly moderate to narrow. Notal edge commonly completely reduced. Ceratal rows usually simple, numerous-to-few non-elevated cerata per row. Rhinophores smooth, rarely annulate. Anus acleioproctic. Masticatory edges of jaws commonly bear single row of compound, tubercle-like or flattened denticles. Radula formula 0.1.0. Central teeth arc-shaped to more narrow, usually with strong to moderately distinct cusp not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens usually short to moderate, prostate indistinct to moderately distinct. Supplementary gland present, inserts into penis, in all confirmed taxa, reports of putative ‘absence’ of supplementary (= ‘penial’) gland are erroneous and based on the failure to identify the existing supplementary gland. Massive external permanent penial collar absent. Penis internal, not considerably broadened, armed with hollow stylet. Stylet present in all confirmed taxa, commonly short, in some cases long.

Remarks: The family Trinchesiidae is the largest, most diverse and most species-rich family within the superfamily Fionoidea . Even the considerable number of currently recognized genera (see above) is definitely not enough to cover the extensive known diversity ( Martynov 2002, Korshunova et al. 2017c, 2022) and more genera need to be separated in a future study of the family Trinchesiidae . The family Pinufiidae , which has previously been largely neglected and rarely mentioned, was considered a family with highly uncertain placement, and never used before 1999 as a family-level taxon of suborder Aeolidacea . Instead, from the time of its first description until very recently it was invariably placed within the completely different suborder Arminacea ( Marcus and Marcus 1960, Rudman 1981, 1982, Jensen 2000, Gosliner et al. 2015), or even one time near the dendronotacean family, Dotoidae ( Pola and Gosliner 2010) . However, Pinufius has most recently been revealed to be closely related to the genus Phestilla of Trinchesiidae ( Jia et al. 2023, present study). Pinufius formed the sister-clade (PP = 1, BS = 87) to Phestilla and clustered within the Trinchesiidae group (PP = 1, BS = 84; Fig. 5A). Therefore, accordingly ‘ Pinufiidae Marcus and Marcus, 1960 ’ is considered a subgroup of Trinchesiidae Nordsieck, 1972 , e.g. as a ‘subfamily’. The family Trinchesiidae , in turn, has been used as a valid name in a significant number of recent articles (e.g. Korshunova et al. 2017a –c, 2018, 2019a, 2021, 2022, Martynov et al. 2019, 2020, Hu et al. 2020a, b, Mehrotra et al. 2020, Picton and Morrow 2023, Jia et al. 2023, and others). Therefore, this case fits within Article 35.5 of ICZN (1999, our italics): ‘If after 1999 a name in use for a family-group taxon (e.g. for a subfamily) is found to be older than a name in prevailing usage for a taxon at higher rank in the same family-group taxon (e.g. for the family within which the older name is the name of a subfamily) the older name is not to displace the younger name’. Thus, the family Trinchesiidae Nordsieck, 1972 , in prevailing usage since 2017, must be kept as a valid taxon.

Surprisingly, instead of gradually continuing the further work of fine-scale genus-level differentiation within the family Trinchesiidae ,whichhasbeenconsistentlyperformed ( Martynov 2002, Korshunova et al. 2017c, 2018, 2019a, Martynov et al. 2020, present study; Figs 1, 2, 5), a strong pan-lumping bias recently led to the alleged ‘synonymy’ of several well-supported (both morphologically and molecularly) trinchesiid genera, using a non-resolved tree full of polytomies with a highly inconsistent taxonomic discussion ( Kim et al. 2024). This immediately resulted in utter chaos in WoRMS (2024) since, for example, some taxa are still assigned to the genera Catriona and Cuthona , whereas others are assigned to the pan-lumping, completely apomorphy-less ‘ Tenellia sensu latissimo ’ genus (see details in: Korshunova et al. 2022). Therefore, we have restored (see above) the incorrectly-synonymized genera, whose validity and morphological and molecular distinctness have been confirmed many times in many recent studies by several research groups (see diagnoses and discussion in: Korshunova et al. 2017a –c, 2018, 2019a, 2021, 2022, 2023, Martynov et al. 2019, 2020, Hu et al. 2020a, b, Mehrotra et al. 2020, 2024) and again restrict the genus Tenellia only to the type species and a few confirmed closely related species (for details see the list above and Korshunova et al. 2022).

Several more genera need to be established within the family Trinchesiidae (this is denoted by quotation marks before the genera name above), especially regarding the obviously heterogeneous and paraphyletic ‘ Trinchesia ’.Importantly, not the narrowly defined genus Trinchesia s.s., with the type species T. caerulea and a few related species, per se ( Korshunova et al. 2019a), but the subsequent lumping events (‘ Cuthona ’, ‘ Tenellia ’) that led to the current situation, when, instead of careful gradual work toward the separation of narrowly defined genera ( Korshunova et al. 2017c, 2022), we now need to again return to some basic constatation, that apart from the narrowly defined genera Zelentia , Trinchesia s.s., Diaphoreolis , Catriona , Tenellia , and Phestilla , a number of separate genera are needed to accommodate the naturally existent, highly intricate morphological and molecular diversity of the family Trinchesiidae . Respectively, many species that are listed above do not precisely match the diagnoses of genera described so far, obviously pending further revision, but again this is the result of the unfortunate persistence of profound negligibility of the fine-scale morphology and taxonomy and not an absence of understanding that, for example, the current ‘ Trinchesia ’, according to morphological and molecular data, is still not a consistent taxon. But, compared, to the super-lumped ‘ Cuthona ’ ( Williams and Gosliner 1979), which turned out to contain representatives of several completely different families (see Synopsis here and above), or the pan-lumped ‘ Tenellia ’ ( Kim et al. 2024), which ‘united’ such immediately different, very easily distinguished taxa as the proper Tenellia (oral veil instead of oral tentacles, few cerata, cnidosacs present, and small size) with Phestilla s.s. (oral tentacles present, numerous cerata, cnidosacs absent, and large size), the current restriction of Trinchesiidae diversity at least to no less than 12 genera, with still significantly heterogeneous ‘ Trinchesia ’ is an important step for further revision of the family Trinchesiidae , when more genera within the former ‘ Trinchesia ’ will be separated to accommodate many fine-scale morphological characters and molecular data. For example, for some of the above listed taxa (e.g. for the genus Narraeolida , reinstated) a penial stylet was not reported in the original description, as well as other inconsistencies with the family Trinchesiidae , but these need in additional study and further confirmation.

Indeed, there are a number of taxa, including undescribed hidden diversity, which have some relationship to Phestilla s.s. or Trinchesia s.s., but demonstrate both morphological differences and sufficient molecular distances, and all these fine-scale differences are pending separation at the genus-level. But along with such cases, there are still many instances, which are the results of many decades of application of the highly imprecise, profoundly polyphyletic ‘concept’ of ‘ Cuthona ’, and which also definitely needs to be addressed. For instance, even some warm-water representatives, like ‘ Cuthona ’ fructuosa ( Bergh, 1892) or ‘ Cuthona ’ destinyae Hermosillo and Valdes, 2007 , according to available morphological data ( Bergh 1892, Ortea et al. 2005, Hermosillo and Valdes 2007) do not belong either to ‘ Cuthona ’ or ‘ Trinchesia ’ s.l., and perhaps do not even belong to the superfamily Fionoidea , and should be considered rather as Aeolidacea incertae sedis. Further, so-called ‘ Cuthona ’ lizae Angulo-Campillo and Valdes, 2003 possesses some features similar to the distantly related family Abronicidae , and perhaps either truly belongs to Abronicidae or represents a case of a convergence within the family Trinchesiidae . These are only a few selected examples of such highly heterogeneous taxa. They, of course, are not limited only to these species, but readily show the pitfalls of the unfortunately persistent pan-lumping approach in nudibranch taxonomy. All these and many other cases, therefore, must not be a reason to synonymyze all the astonishing Trinchesiidae diversity into the diagnoses-less unmanageable taxonomic volume of ‘ Tenellia ’. At the most general scale, the persistent application of the fundamentally overlumped ‘ Cuthona ’ (and the currently overlumped ‘ Tenellia ’ as its logical continuation) for over almost half a century, has profoundly concealed both fine-scale genus-level diversity and also large-scale, family-level diversity first under ‘ Cuthona ’ and now under ‘ Tenellia ’ (see synopsis of the superfamily Fionoidea above). As one of the best examples, not just ‘discussable’ but independent from any consideration, is the fact that when a very significant part of the diversity of many families of the superfamily Fionoidea was lumped into seemingly ‘just single genus Cuthona ’, it was concluded ‘that Trinchesia cannot be separated from Cuthona …’ ( Williams and Gosliner 1979: 212). Remarkably, all subsequent detailed investigations of aeolidacean systematics and phylogeny did not merely ‘not confirm’ that statement, but profoundly abandoned it, since Trinchesia proper and the true Cuthona (instead of the pan-lumped ‘ Cuthona ’) not only are perfectly distinguished from each other morphologically ( Martynov 1992 a, Korshunova et al. 2018, 2019a), but belong to distantly related lineages according to many molecular phylogenetic analyses (summarized in the present study; Figs 1, 2, 5). The true representatives of the genus Cuthona in the family Cuthonidae proper are only so far known three valid species, type C. nana (Alder and Hancock, 1842) , C. divae Er. Marcus, 1961 , and C. hermitophila Martynov et al., 2015 . No other species of the family Trinchesiidae or other families should be currently considered as ‘ Cuthona ’.

Therefore, one more time, true Tenellia is restricted exclusively to only include the well-described valid species Tenellia adspersa (Nordmann, 1845) and Tenellia gotlandica Lundin et al., 2022 , and at a maximum may include the hidden diversity of a few more species, including Tenellia pallida (Alder and Hancock, 1854) and its possible synonym Tenellia fuscata (A.Gould, 1870) (see Korshunova et al. 2022), but, crucially, other taxa of the family Trinchesiidae , must not be placed into that obviously exceedingly overlumped ‘genus Tenellia ’ with its lack of any reliable morphological diagnostic characters and incorrect analysis of the results of the application of molecular data. Importantly, the true Tenellia is well consistent not only in paedomorphic morphology with a well-defined secondarily juvenilized oral veil ( Korshunova et al. 2017c), but highly consistent in the ecological patterns, being predominantly associated with brackish or lowered salinity waters (although able to tolerate higher salinity), such as estuaria and seas with low salinity, such as, for example, the Black Sea, the very type locality of T. adspersa (Korshunova et al. 2022) . Remarkably, the true Tenellia , is the only taxon that is able to penetrate quite far along the upper Thames estuary ( Thompson and Brown 1984), Caspian Sea ( Antsulevitch and Starobogatov 1990), and the most brackish parts of both of the Azov Sea ( Roginskaya 1970, Martynov 2006b) and Baltic Sea, including Finland ( Evertsen et al. 2004) and Russia (our own data). Furthermore, from such peculiar brackish and low salinity habitats, Tenellia adspersa and closely related species were able to widely distribute over the similar habitats in the Northern Hemisphere, using anthropogenic transportation, over 10 000 km, sometimes far from the type locality for example in Japan, where it is immediately recognized exactly as true Tenellia and explicitly considered as an alien (invasive) species (Kashio 2018, Kashio and Hamatani 2018), not as some other Trinchesiidae , and also commonly occurs in some peculiar habitats like port harbours. The specimens from Osaka Bay (Kashio 2018) were studied in Korshunova et al. (2022) and showed strong genetic identity with the T. adspersa from the type locality in the Black Sea. This is the best proof that true Tenellia despite the presence of other described or not yet described genera within Trinchesiidae with partly paedomorphic, independently gained morphology is an immediately recognizable taxon. To ‘synonymyze’ true Tenellia with other diverse genera of the family Trinchesiidae would be similar highly dismissive action as to synonymyze the genus Pan Oken, 1816 with the genus Homo Linne, 1758 , using the priority rule, the misleading designation of ‘overall similar morphology’, and apparently small molecular genetic distances ( Martynov and Korshunova 2022).

Kingdom	Animalia
Phylum	Mollusca
Class	Gastropoda
Order	Nudibranchia
Family	Trinchesiidae