Craspedotropis gretathunbergae, a new species of Cyclophoridae (Gastropoda: Caenogastropoda), discovered and described on a field course to Kuala Belalong rainforest, Brunei

Abstract Background Terrestrial Caenogastropoda form an important but threatened component of the Borneo tropical rainforest malacofauna, where the group is nearly as rich in species as the Stylommatophora. They are, however, more sensitive to drought, temperature extremes and forest degradation. New information On a field course at Kuala Belalong Field Studies Centre in Brunei Darussalam (Borneo), a new caenogastropod species, belonging to the genus Craspedotropis, was discovered by the course participants. The participants decided to name the species Craspedotropis gretathunbergae n. sp., in honour of the climate change activist Greta Thunberg, as caenogastropod land snails, such as this species, are likely to suffer because of climate change.


Introduction
Although Mollusca is, after Arthropoda, the second-most species-rich animal phylum on land (at least in terms of described species), their species numbers are only moderately high compared with the arthropods (Solem 1984, Schilthuizen 2011. Even in hyperdiverse forested regions in the humid tropics, such as northern Borneo, the numbers of known species are in the hundreds, not thousands and trends of discovery appear to be levelling off towards the true number of species. This means that, with relatively little fieldwork effort, it is possible to obtain a more or less complete inventory of the terrestrial malacofauna of a certain area. We are using field courses to several biodiversity hotspots in the world for such a purpose and we use the term 'taxon expeditions' for this (Schilthuizen et al. 2017). Taxon expeditions are a new concept in which a group of taxonomic experts and lay people work together in a hybrid work form of field course and biodiversity discovery expedition to discover unknown species from a given area. On our annual taxon expedition to the Ulu Temburong lowland rainforest in Brunei Darussalam, surveys of terrestrial snails have so far yielded over 25 species. The expected diversity for this type of forest would be around 85 species (Schilthuizen andRutjes 2001, Schilthuizen 2011), but already our inventories are turning up previously unknown species.
In this paper, we describe a new species from the large caenogastropod family Cyclophoridae. In the Southeast Asian tropics, non-Stylommatophora (i.e. Neritopsina and Caenogastropoda) comprise nearly half of the total malacofauna. These snails are, however, more sensitive to habitat disturbance than the Stylommatophora. Studies of malacofauna conservation biology on limestone hills in Sabah have previously shown (Schilthuizen et al. 2005) that these non-Stylommatophora groups are the first to disappear after forest degradation, presumably as a result of lower tolerance ranges for temperature and humidity.
The description of the new cyclophorid that follows is the concerted effort of untrained 'citizen scientists' working together in a field lab. The specific epithet was decided upon during a voting session, in which participants could suggest and vote for scientific names.

Materials and methods
We collected living snails by hand, at night, amongst vegetation along the left (south) bank of the Belalong river, 50 m downstream of Kuala Belalong Field Studies Centre. Specimens were sorted to putative morphospecies and then further examined morphologically with a dissection microscope with 10× and 20× eye pieces. Photographs and video were made either with a smartphone through the eyepiece of a microscope or on a translucent white acrylic sheet with a Nikon D800e fitted with a Laowa 25 mm ultra-macro lens. Drawings were made based on the photographs. Specimens were deposited in the collection of the University of Brunei Darussalam Museum (UBDM).

Nomenclature
Craspedotropis Blanford 1864 sensu Vermeulen (1999 . 1): Protoconch without distinct sculpture; juncture with the teleoconch not visible. Spire high conical, consisting of 5.25 to 5.75 convex whorls. Suture depressed. Radial sculpture: growth lines and densely placed riblets (30-70 per mm on the body whorl). Spiral sculpture: 4 high, prominent, here and there somewhat crenellated radial ribs, which start after 1.5 to 2.0 whorls. The first spiral rib (from the top) is located between the periphery and the suture with the previous whorl. The second sits at the periphery. The third is located near the suture with the next whorl and is visible on the body whorl in some, but not all, individuals. The fourth is located on the basal side and only visible on the edge of the umbilicus. Between the ribs are fine spiral lines. Umbilicus wide, without additional spiral ribs. Height 2.7 -2.9 mm, width 1.7 -1.8 mm.
Operculum (Figs 1, 3): Operculum thin, corneous, whorl margins not raised but flattened into a smooth concave dish, of which the outer part is greenish-brown (presumably because of a thickly applied periostracum), the central part nearly clear.
No calcareous matter visible.

Diagnosis
Amongst the Bornean cyclophorids, Craspedotropis gretathunbergae n. sp. is most similar to C. borneensis (Godwin Austen 1889), which, however, is somewhat less slender, has 7 -9 spiral ribs and more broadly reflected apertural lip. In addition, the operculum of C. borneensis has raised whorl margins, which is not the case in C. gretathunbergae n. sp. Other Asian species, with which the new species may be confused, are: (i) Cyathopoma conoideum Sykes 1898, which has a more slender shell and the spiral ribs arranged in a different pattern, with the second rib located just above the suture; (ii) C. sivagherrianum Beddome 1875, which is smaller, has 7 spiral ribs and a nearly closed umbilicus; (iii) C. beddomeanum Nevill 1881, which has more (7 -8) and more prominent, spiral ribs, more globular whorls and a rounder aperture; (iv) C. procerum Blanford 1868, which is stockier, has 9 -12 spiral ribs and a peristome that is strongly thickened by folds.

Etymology
We name this species in honour of the young climate activist Greta Thunberg, because caenogastropod microsnails from tropical rainforests, like this new species, are very sensitive to the droughts and temperature extremes that are likely to be more frequent as climate change continues. Via mutual contacts, we have approached Ms. Thunberg and learned that she would be 'delighted' to have this species named after her.
Following Recommendation 51C of the Code (ICZN 1999), if it is desired that authorship of the name be included as part of the name, instead of listing all authors, the species can be referred to as Craspedotropis gretathunbergae Schilthuizen et al., 2019, provided that all authors of the name are cited in full elsewhere in the same work, either in the text or in a bibliographic reference.

Ecology
In tropical mixed dipterocarp lowland rainforest. All individuals were found alive at the foot of a steep hill-slope, next to a river bank, foraging at night on the upper surfaces of green leaves of understorey plants, up to 1 m above ground level.

Taxon discussion
The generic classification of minute cyclophorids in Southeast Asia is somewhat confused. The genera Craspedotropis Blanford 1864 , Cyathopoma Blanford 1861 Blanford and Blanford 1861, Jerdonia Blanford 1861 (Blanford and Blanford 1861; sometimes considered a subgenus of Cyathopoma) and Ditropopsis Smith 1897 appear poorly defined and may be partly overlapping or synonymous (Vermeulen et al. 2015, Vermeulen 1999. In its general shell form (a tall conical shell with spiral ribs), the present species is similar to several species of Cyathopoma (e.g. the South Asian C. conoideum Sykes 1898, C. sivagherrianum Beddome 1875, C. beddomeanum Nevill 1881and C. procerum Blanford 1868 and Craspedotropis, especially C. borneensis (Godwin Austen 1889), known from Sarawak. Given the geographical proximity of the latter, we have tentatively placed the new species in the same genus, Craspedotropis.

Discussion
All work described in this paper (fieldwork, morphological study, microphotography, taxonomic description and diagnosis) was carried out in a field centre with basic equipment and no internet access, by untrained 'citizen scientists' guided by expert scientists, on a 10-day taxon expedition. While we are aware that this way of working has its limitations in terms of the quality of the output (for example, we were unable to perform dissections or to do extensive literature searches), the benefits include rapid species discovery and on-site processing of materials.