Subulina bruggenorum, Breure & Ablett, 2018

Breure, Abraham S. H. & Ablett, Jonathan D., 2018, An ironic twist of fate: replacement name for Stenogyra gracilenta Morelet, 1885, not Achatina gracilenta Morelet, 1867 (Mollusca, Gastropoda, Achatinidae), Zootaxa 4418 (3), pp. 299-300 : 299-300

During work on a monograph of Morelet’s contributions to malacology (Breure, Audibert & Ablett, forthcoming) we found that two of his newly introduced taxa currently have to be considered as homonyms belonging to the genus Subulina H. Beck, 1837 (classified within the family Achatinidae according to Fontanilla et al. (2017: 385)). The older taxon is Achatina gracilenta which was described by Morelet (1867: 79, pl. 7 fig. 2) from [ Angola] “Golungo-Alto, au bord du Rio Quiapose, près de Sange; les environs de Lopollo (district de Huilla)”. According to Naggs (1990a: 31; also pers. comm. 10 October 2017) this species has to be classified as Subulina gracilenta ( Morelet, 1867) . The type material of this species is present in the Natural History Museum, London (NHMUK 1893.2.4.263–265). The younger taxon was described by Morelet (1885: 25, pl. 2 fig. 8) as Stenogyra gracilenta from [ Gabon] “environs de Mayumba”. Pilsbry (1906: 82) already recognised this as Subulina gracilenta ( Morelet, 1885) ; Naggs (pers. comm. 10 October 2017) confirmed this classification and concluded that this taxon is a junior secondary homonym of Achatina gracilenta Morelet, 1867 . Type material for Stenogyra gracilenta Morelet, 1885 has not been located. We here propose

Subulina bruggenorum nom. nov.

as a replacement name for Stenogyra gracilenta Morelet, 1885 (not Achatina gracilenta Morelet, 1867 ).

Etymology. We have much pleasure to dedicate this new name to Mrs. Wenda van Bruggen-Gorter and her late husband Dr Dolf (A.C.) van Bruggen.

It should be noted that the systematics of the Subulininae are still poorly known. Gittenberger & Van Bruggen (2013) recently remarked on the study of this group: "It seems reasonable to assume that it is a speciose subfamily, but the delimitation of many alleged species, nearly all of which are based on shell characters only, remains unclear. The number of anatomical, not to mention molecular data, stands in violent contrast with the number of nominal species. Apart from that, many nominal species are only known from their type localities. Several alleged genera cannot be distinguished conchologically because of overlapping shell characters, while anatomical data are not available or too fragmentary, because their type species are insufficiently known. The situation is complicated even more by the variability of the male part of the genital tract and the uniformity of the female part. In several cases, dissection is hampered by the size of the snails and even more so by the fragility of the uterus of these ovoviviparous animals. Also, they start reproducing before maximum size is reached. Therefore there is reason to be cautious with regard to taxa distinguished by size alone."

Whilst it may be best practise to implement nomenclatural acts only when accompanied with a critical taxonomic revision, the authors believe that in this case the designation is appropriate.

Naggs (1990a, 1990b) evaluated and revised the generic placement of all known species up until that point, and followed Zilch's generic system. The current understanding of the genus Subulina is that these species are congeneric (Naggs, pers. comm. 13th March 2018).

In the case of the available type material, we currently only have the shells of Achatina gracilenta Morelet, 1867 and a figure of Stenogyra gracilenta Morelet, 1885 to evaluate the generic placement of the species. Given anatomical and molecular information we would of course be in a position to further refine our understandings of these two species. Looking at the shells of each taxa it can be seen that there are difference in terms of shell sculpture; Stenogyra gracilenta Morelet, 1885 has a finely striated shell where as Achatina gracilenta Morelet, 1867 has a prominently striated shells.

However we feel that it is not appropriate to place these species in separate genera based on shell characters alone, and so the replacement name is an appropriate measure. For example, the genus Striosubulina Thiele, 1933 , that was erected as a monotypic generic category for Subulina striatella (Rang, 1831) , based on the strong sculpture of the shell compared to the smooth shell of the type species of Subulina , Subulina octona . Naggs made a detailed study of the penial structure of Subulina striatella and, as with the full range of characters of the reproductive organs proximal to the genital orifice, it was indistinguishable from that of Subulina octona (unpublished, Naggs, pers. comm. 13th March 2018). Although unpublished, this congeneric relationship was confirmed by the molecular study of Fontanilla et al. (2017). As more genetic and anatomical data appear it is of course possible that Stenogyra gracilenta Morelet, 1885 may prove not to be placed in Subulina (as of course could Achatina gracilenta Morelet, 1867 ) and future taxonomists may feel it appropriate to resurrect the original species name of gracilenta Morelet, 1885 for this taxon. Thus the authors acknowledge this name should be considered a placeholder only until future revisionary work is done.

In the NHM collections the only other Subulina species recorded from the regions around where the types of Stenogyra gracilenta Morelet, 1885 and Achatina gracilenta Morelet, 1867 were found are; Subulina normalis ( Morelet, 1885) , Subulina petrensis (Morelet, 1866) and Subulina striatella (Rang, 1831) . Since none of these species is a known or likely senior synonym of Stenogyra gracilenta Morelet, 1885 , we believe that in this instance the replacement of the junior homonym need not await completion of a comprehensive revisionary work.

Morelet described 738 new taxa, of which 52% are from Africa. Although he seems to have been a careful taxonomist (we found few homonyms in his taxa list), he was also old-fashioned when it came to the classification in genera. He preferred the sensu lato interpretation and repeatedly indicated in correspondence to H. Crosse he was not in favour of the work of A. & H. Adams (1853 –1858) who split many genera like Helix and Bulimus . Nevertheless he reluctantly started to follow this framework in his later work. The fact that two species described by Morelet in different genera more than 130 years later appear to be secondary homonyms, may thus be considered as an ironic twist of fate.