Dadagulella minuscula subsp. mahorana Rowson & Tattersfield 2013, subsp. nov.
Creators: name: Rowson, Ben
name: Tattersfield, Peter
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Streptaxidae
Dadagulella
Dadagulella minuscula
Dadagulella minuscula mahorana

description: Dadagulella minuscula mahorana subsp. nov.
Figs 40, 64, 84; Table 1
? Ennea (Uniplicaria) fischeriana “grössere Form auf Mayotte ” – Kobelt 1905: 166.
Etymology
From English noun or adjective ‘Mahoran’, denoting a person or thing from Mayotte; Latinized by the addition of the feminine ending ‘- a ’ and used as a noun in apposition.
Type material examined
MAYOTTE: holotype NMW.1955.158.25051: 1 ad., “ Mayotte I. ”, standing as “ fischeriana ”. Paratypes NMW. 1955.158.25065: 2 ad., data as holotype.
Type locality
Mayotte (approx. 12.85°S, 45.15°E), Comoros archipelago.
Other material examined
MAYOTTE: NHMUK.1882.5.27.6-7: 2 ad., “Mayotte” (approx. 12.85°S, 45.15°E), standing as “ fischeriana ”. NHMUK.20110171: 2 ad., “Mayotte”, standing as “ fischeriana ”. RMNH.MOL.273928: 1 ad., “Mayotte”, standing as “ fischeriana ”.
Description
SHELL (Figs 40, 64). Variable in size, shape and dentition, large (4.30 - 4.60 mm high x 1.90 - 2.20 mm wide), of 6.5 - 7.5 whorls. Ovate-acuminate, spire narrowly acuminate to coeloconoid (spire angle 50 - 57°). Apex pointed. Embryonic whorls smoothly granulate. Subsequent whorls with finer, much more numerous ribs than the lectotype of D. r. radius comb. nov. (15 - 23 per mm on penultimate whorl). Sutures relatively deep. Umbilicus closed or nearly so. Peristome complete, or incomplete parietally. Outer palatal surface of aperture with a depression corresponding to the palatal tooth. Dentition 6-fold, consisting of: one lamella-like parietal tooth, sometimes slightly bifid; one slab-like palatal tooth, often bifid, but with parieto-palatal sinus barely present; one basal denticle; two shallow columellar denticles; and one deep-set columellar baffle, folded and sub-trifid, always visible. Shells and anatomy of juveniles unknown.
Range and habitat
Mayotte; habitat unknown.
Remarks
This Mayotte subspecies is here separated from its counterpart on Nzwani for the first time. Specimens of Dadagulella gen. nov. species from Mayotte were first discussed by Morelet (1881) under his proposed replacement name for Pupa minuscula (see above). He noted specimens from Mayotte were larger and had more complex dentition than those from Anjouan. Tryon (1885) and Kobelt (1905) followed Morelet in treating D. fischeriana (i.e. D. minuscula comb. nov. s.l.) as a variable species that was present on the “ Comoros Islands” (Tryon 1885) or on Anjouan, with a “grössere Form auf Mayotte ” (Kobelt 1905, although his dimensions of 9 mm x 2 mm must be erroneous). Both authors appear to have copied Morelet’s (1877) figure of the lectotype of D. m. minuscula comb. nov., unless they saw material very like it, and appear to have repeated (translated) Morelet’s (1881) comments on dentition. Tryon (1885) says “sometimes the parietal lamina is accompanied by a more profound very small tooth” but this may be a misinterpretation of Morelet’s (1881) “le pli pariétal peut être accompagné d’une très petite denticule plus profonde”, with “plus profonde” meaning ‘deeper’, rather than ‘profound’, i.e. ‘more obvious’ or ‘more important’. Morelet’s “denticule” is likely to refer to the bifid shape of the parietal tooth, rather than to an additional parietal denticle (like that of D. browni comb. nov. s.l.) which is not present in any of the specimens of D. minuscula comb. nov. s.l. we examined. It is not clear to which of the other teeth Morelet’s (1881) “cinquième petite dent, dans la gorge de la coquille” refers, because all Mayotte specimens we examined have 6-fold dentition. It could even be the fifth tooth, i.e. the shallow columellar denticle, of the paralectotype of D. m. minuscula comb. nov., since Morelet (1881) is not explicit about the shell he is referring to. This raises another unfortunate possibility: that the paralectotype of D. m. minuscula comb. nov., apparently from Anjouan, was in fact a specimen without type status that was added later, and may even have come from Mayotte (or elsewhere), which would accord with Morelet’s (1881) amendments to his description. However, we have no other reason to doubt the existing labels.
We here introduce the name D. m. mahorana subsp. nov. for the larger, coeloconoid specimens from Mayotte, the name fischeriana Morelet being unavailable (see above). They are indeed larger than the two specimens of D. m. minuscula comb. nov. (the size ranges do not overlap), are more elongate, have a more coeloconoid spire, finer and more numerous ribs, and 6-fold dentition including two shallow columellar denticles. These same features also distinguish them from D. radius comb. nov. s.l., which they overlap in size but only barely in the higher number of ribs per millimetre. Although as with D. radius comb. nov. s.l., it is difficult to distinguish intra- and interspecific variability, it is clear that the differences between the holotype of D. m. mahorana subsp. nov. and the lectotype of D. m. minuscula comb. nov., each collected on different islands, are substantial and sufficient for most modern authors to consider them distinct species. Alternatively, and given the residual uncertainty about the paralectotype of D. m. minuscula comb. nov., they may form part of a complex of subspecies. Again, further data is needed to address this.
description: Published as part of Rowson, Ben & Tattersfield, Peter, 2013, Revision of Dadagulella gen. nov., the " Gulella radius group " (Gastropoda: Streptaxidae) of the eastern Afrotropics, including six new species and three new subspecies, pp. 1-46 in European Journal of Taxonomy 37 (37) on pages 29-30, DOI: 10.5852/ejt.2013.37, http://zenodo.org/record/3806770