Chudidae, Korshunova & Fletcher & Martynov, 2025

Family Chudidae fam. nov.

( Figs 1, 2, 6; Table 4)

urn:lsid:zoobank.org:act:

Etymology: The name for the new family and genus is derived from the Russian ‘ chudo ’, which means ‘amazing thing’ and ‘miracle’, initially as a reference to the extraordinary set of both external and internal characters in Chudo gen. nov. and Chudidae fam. nov. ( Fig. 6) (stem is defined as ‘Chud-’), but with the addition of the species’ name ‘humanistica’ (Latin and Russian for humanism, humanity-adhered) in the binomen Chudo humanistica gen. et sp. nov. it forms a most general meaning as an ideal hope in one of the most difficult times in the world.

Diagnosis: Body considerably wide and massive. Notal edge completely reduced, dorsal part of the body smoothly transits to the lateral part. Ceratal rows distinct areas, partly compound, separate, moderate in number, not stalked. Rhinophores smooth to wrinkled. Anus partly mixed—pleuroproctic in a higher cleioproctic position, in an extreme posterior body placement. No elaborate oral glands. Masticatory edges of jaws smooth. Radula formula 1.1.1. Triserial radula is remarkable with very massive lateral teeth. Central teeth square to triangular, with a strong non-compressed cusp. Both central and lateral teeth bear numerous fold-like, partly clustered denticles. Single distal receptaculum seminis present. Vas deferens long, convoluted, prostate non-distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Definite penis not detected.

Remarks: The new deep-sea family Chudidae fam. nov. and Chudo humanistica gen. and sp. nov. fundamentally differ from all the nearly 30 currently known aeolidacean families by both external and internal morphological data [see Synopsis of all Aeolidacean families in the present study throughout the text, Korshunova et al. (2017a), and additionally in Martynov et al. (2019, 2020)], and by molecular phylogenetic data ( Figs 1, 2; Tables 1–4).

After the clarification of the system of aeolidacean superfamilies (see above, after the diagnosis and Remarks to the suborder Aeolidacea ), we now present a detailed consideration of the taxonomic placement of the new superfamily Chudoidea superfam. nov. and family Chudidae fam. nov.. In particular, Chudidae fam. nov. differs from any families of the predominantly triserial superfamily Flabellinoidea by the presence of a very broad body with completely reduced notal edge and the presence of distinct, non-continuous ceratal rows ( Fig. 6), as well as a partly mixed pleuroproctic in a higher cleioproctic position of the anus, in a remarkably far posterior body placement (such placement is very rare among Aeolidacea , a partially similar condition known mostly within the family Murmaniidae of the superfamily Fionoidea , which is completely different from Chudidae fam.nov. by a number of external and internal features; see Synopsis above) along with the extraordinary patterns of the triserial radula with extremely massive lateral teeth ( Fig. 6F–H). Chudidae fam. nov. differ from any families of the superfamily Aeolidioidea by the presence of a triserial radula, the posterior position of the anus, as well as details of its external features and reproductive system. Chudidae fam. nov. readily differ from an absolute majority of the families of the superfamily Fionoidea by a triserial radula and the absence of a supplementary gland in the male reproductive system. The only family within Fionoidea that possesses a triserial radula is Eubranchidae , which, however, is fundamentally different from Chudidae fam. nov. by the very different shape of its central and lateral teeth.

Furthermore, all Eubranchidae possess a reproductive system with a distinct supplementary gland, very different from Chudidae fam. nov.. Ironically, the only family within Fionoidea that does not possess a supplementary gland is the stem-genus bearing family name Fionidae , which, however, differ from Chudidae fam. nov. by the presence of a uniserial radula, the presence of a notal edge, and their general body pattern. From the triserial superfamily Cumanotoidea and family Cumanotidae , Chudidae fam. nov. differ by the distinctly posterior pleuroproctic in a higher cleioproctic position of its anus instead of the acleioproctic position of the anus in the anterior to middle part of the body, the very different general pattern of the radula with massive plate-like lateral teeth instead of hookshaped lateral teeth, by the absence of special clasping structures in the female reproductive system, as well as the absence of a detectable penis. Chudidae fam. nov. differ from the highly paedomorphic family Pseudovermidae (phylogenetically related to Cumanotidae , but morphologically dramatically different) by their completely different body shape, ceratal patterns, anus position, as well as details of the radula and reproductive system. From the uniserial superfamily Unidentioidea and family Unidentiidae , Chudidae fam. nov. fundamentally differ by their general body pattern, patterns of their triserial radula, and details of the reproductive system. Chudidae fam. nov. also differ from two of the basal triserial aeolidacean superfamilies, Apataoidea and Samloidea , by their general body pattern, posterior pleuroproctic to higher cleioproctic anus, and the very different pattern of their triserial radula and reproductive system. Chudidae fam. nov. substantially differ from one of the basal-most aeolidacean superfamily, Notaeolidioidea (unique within the suborder Aeolidacea in that they preserve an oligoserial ancestral radula), by their triserial radula, the absence of a notal edge, the position of the anal opening, and by details of the reproductive system.

According to the molecular phylogenetic analysis in the present study, Chudidae fam. nov. are either sister to the superfamilies Aeolidioidea , Flabellinopsoidea , and Flabellinoidea ( Figs 1, 2) or sister to superfamilies Cumanotoidea , Flabellinopsoidea , and Flabellinoidea ( Fig. 2), although in both cases with low support, which in turn supports the recognition of a separate superfamily, Chudoidea superfam. nov., since this unique new superfamily and family are not directly related to any aeolidacean families so far described (see Synopsis above and below), either from morphological patterns ( Fig. 6), or according to the molecular phylogenetic data ( Fig. 2). It is important to note that an absolute majority of the taxa within the suborder Aeolidacea possess either a triserial or uniserial radula ( Fig. 2; Tables 1, 2) and the overwhelming presence of multiserial to oligoserial radulae within the outgroup of non-aeolidaceans (represented in the present analysis by the families Tritoniidae and Janolidae , Figs 1, 2; Tables 1, 2). The family Notaeolidiidae has already been morphologically supported as an early diverged taxon within Aeolidacea ( Wägele 1990, Wägele and Willan 2000), and possesses an ‘intermediary’ oligoserial radula (with the number of longitudinal rows of the lateral teeth in total less than 10; Fig. 2; Tables 1, 2), thus less than the usual multiserial radula, but at the same time obviously more rows than a triserial radula (with only two longitudinal rows of the lateral teeth flanked by central teeth from each side), the triserial condition most likely preceded the uniserial radula in the evolution of Aeolidacea (see also character states justification in: Martynov et al. 2020). Next, the distribution of the triserial radulae among various aeolidacean superfamilies ( Fig. 2) fits into a phyloperiodic pattern of evolution ( Martynov and Korshunova 2022, present study; Tables 1, 2) because several superfamilies, including Flabellinopsoidea and Fionoidea , possess both triserial and uniserial families, and the new triserial superfamily Chudoidea superfam. nov., is related, although not precisely, to a node around both triserial Cumanotoidea and Flabellinoidea , along with uniserial Aeolidioidea , but not to other aeolidacean superfamilies ( Figs 1, 2; see Synopsis of all Aeolidacean families throughout the text).

However, the relative proportion of triserial and uniserial families within each superfamily varies greatly ( Fig. 2; Tables 1, 2). For example, all Flabellinoidea are triserial, whereas within Flabellinopsoidea there is only one exception so far, the newly described uniserial flabellinopsoid family, Hantazuidae fam. nov. (see Synopsis below). In turn, almost all families of the superfamily Fionoidea (with the exception of the triserial family, Eubranchidae ) are instead uniserial ( Fig. 1, see Synopsis above). In the third largest aeolidacean superfamily recognized here, Aeolidioidea (after the exclusion of the previously incorrectly assigned members of the distantly related superfamily Flabellinoidea ; see Synopsis below) include only a kernel of the closely related families such as Aeolidiidae , Myrrhinidae , Facelinidae , Favorinidae , Glaucidae , Babakinidae , and Pleurolidiidae ( Figs 1, 2; Synopsis below)—the true aeolidioidean families—where triserial radulae are unknown. Considering that the three basal-most ‘smaller’ aeolidacean superfamilies recognized here (see Synopsis above and below), corresponding to the three phylogenetically basal but morphologically highly disparate families, Apataidae , Samlidae , and Notaeolidiidae (sister to all other aeolidaceans; Figs 1, 2), are all either oligoserial or triserial, and that the triserial condition is present in all major aeolidacean superfamilies ( Fig. 2), the triserial condition is likely the ancestral condition for all Aeolidacea , except Notaeolidiidae . The latter family is therefore last modern relic of the pre-triserial ancestral aeolidacean initial radiation.

Whether the superfamily Chudoidea superfam. nov. will prove to have either a closer relationship to the superfamily Aeolidioidea ( Fig. 2) or a somewhat more ‘intermediate’ position toward the superfamilies Cumanotoidea , Flabellinopsoidea , and Flabellinoidea ( Fig. 2), its discovery is a very important step for the comprehensive understanding of the evolution and systematics of the suborder Aeolidacea , because the pattern of the proportions of the triserial and uniserial families ( Fig. 2; Tables 1, 2), and the high probability of the ancestral triserial state discussed above, clearly suggest that the triserial condition can relatively easily be reduced as an ontogenetic event over the course aeolidacean evolution, which, therefore, facilitates the formation of a uniserial radula multiple times in almost all major aeolidacean groups ( Fig. 2; Tables 1, 2). A perfect example of such independent formation of a uniserial radula is the new family Hantazuidae fam. nov., which is uniserial but robustly placed as sister to the firmly triserial Flabellinopsidae , generally within the otherwise triserial superfamily Flabellinopsoidea ( Fig. 2). The triserial superfamily Chudoidea superfam. nov. and Chudidae fam. nov. may, therefore, represent in turn some relic ‘core’, ‘mid-evolutionary’ aeolidacean radiation (that is partly reflected in their low support as sister to superfamilies Aeolidioidea , Cumanotoidea , Flabellinopsoidea , and Flabellinoidea ; Figs 1, 2) preserved in the deep-sea environment, based on which the subsequent definite superfamilies, either predominantly triserial such as Flabellinoidea and Cumanotoidea , or predominantly uniserial, such as Aeolidioidea have been ‘finally’ formed ( Fig. 2).

Chudo gen. nov. ( Figs 1, 2, 6) urn:lsid:zoobank.org:act:

Type species: Chudo humanistica gen. et sp. nov..

Diagnosis: Body considerably wide and massive.Notal edge completely reduced, dorsal part of the body smoothly transits to the lateral part. Ceratal rows distinct, separate, moderate in number, not stalked. Rhinophores smooth to wrinkled. Anus partly mixed—pleuroproctic in a higher cleioproctic position in an extreme body placement. No elaborate oral glands. Masticatory edges of jaws smooth. Radula formula 1.1.1. Triserial radula is remarkable with very massive lateral teeth. Central teeth square to triangular, with a strong non-compressed cusp. Both central and lateral teeth bear numerous fold-like, partly clustered denticles. Single distal receptaculum seminis present. Vas deferens long, convoluted, prostate non-distinct. Massive external permanent penial collar absent. Definite penis not detected.

Remarks: See above after the new family diagnosis.