Hexabranchus praetextus Ehrenberg, 1828

Tibiriçá, Yara, Pola, Marta, Pittman, Cory, Gosliner, Terrence M., Malaquias, Manuel A. & Cervera, Juan Lucas, 2023, A Spanish dancer? No! A troupe of dancers: a review of the family Hexabranchidae Bergh, 1891 (Gastropoda, Heterobranchia, Nudibranchia), Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 697-742 : 727

Hexabranchus praetextus Ehrenberg, 1828 (Fig. 26B)

Description notes short description based on external features: flattened body; foot narrower than mantle; red notum; white margin; six gill branches arranged around anus in separate gill pockets; oral tentacles serrated.

Own conclusion/opinion on its taxonomic status There is no doubt that H. praetextus and H. sanguineus represent the same species. H. praetextus and H. lacer were declared nomen oblitum by Valdés (2002) based on ICZN Art. 23.2. The International Code of Zoological Nomenclature (2000) establishes that such action can be done when two conditions are met: (1) Art. 23.9.1.1, the senior synonym has not been used as valid after 1899, and (2) Art. 23.9.1.2, the junior synonym has been used in at least 25 publications by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years. Despite H. sanguineus being extensively used in the literature by almost all authors, H. praetextus was cited as valid in at least one publication after 1899 (see Vayssière, 1912). Therefore, contrary to what was stated by Valdés (2002), condition 23.9.1.1 was not met. Nevertheless, according to the code, “if action taken under Article 23.9.2 is found later to have been taken in error in those conditions 23.9.1.1 and 23.9.1.2 were not met, the case is to be referred to the Commission. Prevailing usage must be maintained [Art. 82] until the Commission has made a ruling.”

Taking into account article 23.9.3 which says “If the conditions of 23.9.1 are not met but nevertheless an author considers that the use of the older synonym or homonym would threaten stability or universality or cause confusion, and so wishes to maintain use of the younger synonym or homonym, he or she must refer the matter to the Commission for a ruling under the plenary power [Art. 81],” we highly recommend that H. sanguineus remains the valid name. Our recommendation is based on the fact that an action of erroneous reversal of precedence would add even more confusion to the literature. Additionally, H. sanguineus is a popular name among the scientific and non-scientific community and has been used in all recent field guides and manuscripts.