NEW SPECIES OF MIRADISCOPS (GASTROPODA: SCOLODONTIDAE) FROM MARTINIQUE

Martinique. This emphasises the importance of Mount Vauclin as a home to endemic invertebrates on the island and the need for collection efforts that includes soil and leaf litter sampling.


INTRODUCTION
Terrestrial molluscan island diversity is often characterised by high levels of endemism (cooK 2008, chiBa & cowie 2016, yeunG & hayeS 2018, ProioS et al. 2021).This pattern is particularly interesting in the Antilles, with high levels of diversification in the Greater Antilles but an apparently reduced richness in the Lesser Antilles (e.g., roBinSon et al. 2009, van Leeuwen et al. 2015, hoveStadt & van Leeuwen 2017, hoveStadt & necKheim 2020).
Only 17 endemic land snail species are so far known on the Lesser Antillean island of Martinique (deLannoye et al. 2015, GarGominy et al. 2022), which is about 40% of the number known on its similar-sized island neighbour Dominica (roBinSon et al. 2009).Most of the species recorded from Martinique are macrogastropods, which are easily visible and thus, easier to find; while species of microgastropods (e.g., Punctoidea, Scolodontidae) often remain undersampled and overlooked (SaLvador 2019).
Herein, we describe a new species of scolodontid snail from Martinique collected by the second author based on material obtained from sifted soil and leaf litter.This is the second species of Scolodontidae recorded from the island.

MATERIAL AND METHODS
The specimens analysed in the present study are deposited in the malacological collection of the Muséum national d'Histoire naturelle (MNHN; Paris, France) and consist of dry empty shells collected from ground sieving by the second author during a one-day trip to Mount Vauclin.Scanning electron microscopy (SEM) was conducted at the Victoria University of Wellington School of Chemical and Physical Sciences (Wellington, New Zealand).All images were captured on a JEOL 6500F Scanning Electron Microscope (JEOL Ltd., Japan) (55-170× magnification).Selected shells were mounted in the desired orientation on aluminium stubs using carbon tape and placed in the vacuum desiccator overnight to facilitate carbon coating and remove volatile substances that can result in artifacts during the process.All samples were collectively coated with 3 rods of graphite-carbon at approximately 24 nm of thickness per rod.
The following abbreviations are used throughout: H -shell height (parallel to the columellar axis); Dgreatest shell width (perpendicular to H); h -aperture height (parallel to H, from the apical insertion of the lip to the basal region of the lip).All measurements were conducted on the free public domain image processing software ImageJ v.

DISCUSSION
Miradiscops madinina sp.nov.exhibits a minute discoid and sculptured shell characteristic of some Scolodontidae and also of Punctoidea snails in the Neotropics.It can be placed in the genus Miradiscops due to its unique proto-and teleoconch sculpture consisting of spiral rows of microscopic pits (thieLe 1931, ziLch 1960, SchiLeyKo 2000).Importantly, the protoconch sculpture is not easily visible under a stereomicroscope (Fig. 8), but SEM enables a clear perspective (Figs 5,10).Under the stereomicroscope, the protoconch can appear smooth or sculptured by spiral cordlets, depending on magnification.
The shell of Miradiscops madinina sp.nov. is characterised by a profile of rounded whorls, a lightly flattened spire, a D-shaped aperture, and a marked teleoconch sculpture, all of which contribute to an easy diagnosis when compared to most of its congeners.All species of Miradiscops share the characteristic rows of microscopic pits including the type species M. variolata, as well as M. brasiliensis (Thiele, 1927), M. lunti (E. A. Smith, 1898), M. panamensis Pilsbry, 1930, M. punctata (H. B. Baker, 1925), M. puncticipitis (Pilsbry, 1926), and M. youngii Dourson, Caldwell et Dourson, 2018.
Miradiscops madinina sp.nov.has a slightly more flattened spire than its congeners, which gives the shell a more discoid aspect; the exception is M. punc ticipitis, which has an even flatter spire compared to the new species.Likewise, M. madinina sp.nov.has a D-shaped aperture, narrower than most congeners, which have wider and more circular apertures; the exceptions are M. puncticipitis and M. brasiliensis, whose apertures have a similar shape to that of the new species.Miradiscops puncticipitis and M. brasiliensis are conchologically the most reminiscent of M. madi nina sp.nov.The most obvious diagnostic feature for identifying M. madinina sp.nov.from those species and its other congeners, however, is its marked teleoconch sculpture: the axial striae are stronger and more regularly spaced, being rib-like in their appearance (in other Miradiscops spp., the striae are fainter and more irregular).
The specimens of Miradiscops madinina sp.nov.studied here were collected in leaf litter on top of Mount Vauclin.The area is within protected secondary forest and a biodiversity hotspot in Martinique (BaiLLard & JoSePh 2015), which suggests that this new species is native to the island.The present report represents the first record of Miradiscops stricto sensu from the whole volcanic arc of Lesser Antilles; Further collection efforts should concentrate on observing and obtaining live specimens, which would allow us to understand its natural history as well as enable the description of internal anatomy and acquiring DNA sequence data for barcoding and phylogenetic work.A focus on collecting microgastropods by sieving soil and leaf litter is a key path to the discovery of other undetected species.Land snail biodiversity is much less understood in the Lesser Antilles compared to their marine counterparts.It is highly probable that undersampled microgastropods are more prevalent on these islands than initially thought and could thus, provide interesting cases for biogeographical and evolutionary studies.

Figs
Figs 1-3.Collection site: 1 -overview of the top of Mount Vauclin (photo by e. Poirier); 2 -the mesophyllous forest of top Mount Vauclin (photo by t. ramaGe); 3 -place where the specimens were collected (photo by t. ramaGe)