A molecular and conchological dissection of the “scaly” Georissa of Malaysian Borneo (Gastropoda, Neritimorpha, Hydrocenidae)

Abstract The Bornean hydrocenids have so far been understudied compared to other non-pulmonate snails in this region. In the present study, we review a first group of minute land snail species belonging to the genus Georissa (Gastropoda, Hydrocenidae) from Malaysian Borneo. This group is restricted to the species with conspicuous scale-like sculpture on the shell. Based on materials from recent fieldwork, museums, and personal collections, Malaysian Borneo hydrocenids are more complex and diverse in shell characters than previously anticipated. Here, a molecular, conchological, and biogeographic study of this “scaly group” is presented. We recognise 13 species of which six are new to science, namely Georissa anyiensis sp. n., Georissa muluensis sp. n., Georissa bauensis sp. n., Georissa silaburensis sp. n., Georissa kinabatanganensis sp. n., and Georissa sepulutensis sp. n.


Introduction
Over the past 25 years, the microsnail fauna of karst habitats in South East Asia has enjoyed an ongoing surge of attention. Detailed conchological and molecular studies in this region have revealed high allopatric and sympatric diversity (e.g., Liew et al. 2014, Rundell 2008, Tongkerd et al. 2004), which has opened up this fauna for work in the fields of community ecology , Schilthuizen 2011), speciation , Schilthuizen et al. 2012, and conservation biology (Clements et al. 2006, Clements et al. 2008. Although several families of non-pulmonate snails have featured prominently in these studies (in particular the Diplommatinidae and other cyclophoroids), the family Hydrocenidae (Neritimorpha) has so far been understudied. In this paper, we make a start with a first conchological and molecular characterisation of a surprisingly diverse group of species in the genus Georissa Blanford, 1864. The genus Georissa Blanford, 1864 is characterised by a calcareous, rounded to ovate concentric, paucispiral operculum, with a calcareous peg emerging from the inner surface (Bandel 2008, Vermeulen et al. 2015. The shell is small, dextral, conical, and frequently presents conspicuous radial and spiral sculpture. The studies by Thompson and Dance (1983) and Vermeulen et al. (2015) showed that the Bornean Georissa are between 0.7 and 4.0 mm in adult shell height. The protoconch is usually distinctly hemi-spherically shaped, distinct in microsculpture and distinguishable from the post-embryonic whorls. The internal walls (some would refer these as septa) are resorbed, and the remaining wall ends more than one whorl before reaching the aperture; resorption also leads to excavation of the columella (Thompson andDance 1983, Bandel 2008). The evolutionary causes for this internal shell restructuring remain to be studied. The snails are often found in moderate to high densities on rocks, especially limestone rocks, where they apparently forage moss, algae, and lichens (Berry 1966). Cave-adapted species may forage on bacterial films (Schilthuizen et al. 2012).
Previous taxonomic treatments of Bornean Georissa (Godwin-Austen 1889, Gredler 1902, Haase and Schilthuizen 2007, Smith 1893, 1895, van Benthem-Jutting 1966, Vermeulen and Junau 2007, Vermeulen et al. 2015 revealed that shell shape and size, as well as sculptural patterns on the whorls are important characters for species delimitation. Given the small size of these shells, great benefits can be had from the use of scanning electron microscopy and X-ray microtomography, which are able to show detailed microscopic sculpture patterns and the inner part of the shell. Since the overview presented by Thompson and Dance (1983), no revisions have been made for the Bornean Georissa, although recently, several new Bornean Georissa have been described, i.e., Georissa filiasaulae Haase & Schilthuizen, 2007, Georissa pachysoma Vermeulen & Junau, 2007, Georissa leucococca Vermeulen et al., 2015 and Georissa nephrostoma Vermeulen et al., 2015. Our new studies of the Georissa of Malaysian Borneo reveal additional, previously unrecognized diversity, which warrants a measurements of "scaly" Georissa were carried out following the shell measurement method of Vermeulen and Whitten 1998. Scanning electron microscopy. A representative adult shell for each species was cleaned using sodium hypochloride, dried, and sputter-coated with Pd/Pt coating agent before detailed examination with a JEOL JSM-6480LV scanning electron microscope (SEM). We obtained SEM images of the entire shell in top view and apertural view (including clear view of the sculpture), side and top views of the protoconch and the spire. Micro-computed tomography. The micro-computed tomography (µCT) scanning was carried out with an Xradia 520 Versa X-ray Microscope using accompanying software Zeiss Xradia Versa (11.1.6315). The X-ray images from the scanning (ca. 950 layers of images in TIF format) were reconstructed into composite 3D images of the shells using software Scout-and-Scan TM Control System Reconstructor (11.1.5707.17179). All shell materials were scanned in air medium at 80/7 voltage/power (kW/P) using objective lens unit 4 in 180° rotation. Detailed scanning parameters for each species are summarized in Suppl. material 1. We used reconstructed 3D images of representative adult shells of each species from µCT scanned data to examine the internal characters, including the operculum and its peg. We conducted 3D image reconstruction to preserve the original structure of the shells and avoiding unintentional shell destruction. The 3D image analysis of the shells was carried out with Avizo ver. 9.2.0, FEI Company.

Sequence alignment and phylogenetic analyses
Sequence data and alignement. A total of 12 ingroup taxa of "scaly group" Georissa including an outgroup taxon, Georissa gomantongensis Smith, 1893, were used for phylogenetic analyses (using a much larger hydrocenid taxon sampling, to be published elsewhere, we confirmed that G. gomantongensis indeed branches off basally to the "scaly group"). We added another six 16S mtDNA sequences from GenBank, representing Georissa saulae (van Benthem-Jutting, 1966) (GenBank accession no. AY547380, AY547381, AY547384, and AY547385) and Georissa sepulutensis sp. n. (GenBank accession no. AY547387 and AY548388). We conducted our phylogenetic analyses based on 128 sequences for 16S and 91 sequences for CO1. The forward and reverse nucleotide reads were assembled using de novo Geneious 10.0.7 assembler, manually checked and edited, and later aligned using default settings of MUSCLE alignment (Edgar 2004). Phylogenetic inference. For CO1 sequences, we selected the invertebrate mitochondrial genetic code at the second reading frame. Ambiguous nucleotide sequence ends were trimmed and removed prior to further analysis. ModelFinder (Kalyaanamoorthy et al. 2017) was used to select the most appropriate model, based on the corrected Akaike Information Creterion (AICc) for partial 16S and CO1 mtD-NA genes. The best fitting models were TIM3+F+I+G4 for 16S and TIM2+F+I+G4 for CO1. Phylogenetic analysis. Maximum likelihood analysis was performed using IQ-TREE 1.6.3 (Nguyen et al. 2014) on a concatenated 16S and CO1 sequences of "scaly" Georissa using TIM3+F+I+G4 as the nucleotide substitution models with ultrafast bootstrapping (1000 replicates) (Hoang et al. 2017). Bayesian Inference was performed using MrBayes 3.2.6 (Huelsenbeck and Ronquist 2001) with the next closest nucleotide substitution model, GTR+I+G using the following MCMC settings: Chain length = 1,100,000 generations, heated chain = 4, subsampling frequency = one tree for each 200 generations, burn-in length = 100,000, and chain temperature = 0.2.

Species delimitation and description
For species delimitation, we combined the data of molecular phylogenetic analyses and the assessments of the morphology. We aimed for monophyly in species, allowing paraphyly under certain circumstances (Schilthuizen and Gittenberger 1996), but disallowing polyphyly. Only when we found morphological characters that could distinguish DNA-based clades or paraphyletic groups, did we consider such groups as potential species. Although many forms in Georissa are allopatric, we did have a number of cases where two forms occurred sympatrically without forming intermediates, which also aided in determining species status by application of the biological species concept (Mayr 1942). General shell characters were further divided into detailed subcharacters exclusively for the descriptions of the representatives of the "scaly group" of Bornean Georissa. The assessed morphological characters follow the descriptions made by Godwin-Austen (1889), Gredler (1902), Haase and Schilthuizen (2007), Smith (1893Smith ( , 1895, Thompson and Dance (1983), van Benthem-Jutting (1966), Vermeulen and Junau (2007), and Vermeulen et al. (2015). Note that color indications always refer to living or freshly dead specimens, as the color in older specimens usually degrades, with an exception for Georissa scalinella (van Benthem-Jutting, 1966), where only old collection specimens were available.

CO1 genetic divergence
In addition to the molecular phylogenetic and morphological assessment in our species delimitation, we conducted divergence analysis of partial CO1 genes to provide additional information to assist in the species delimitation of "scaly" Georissa. Several other studies on species delimitation in gastropods have also used CO1 mtDNA successfully (see Liew et al. 2014, Puillandre et al. 2012a, 2012b. Pairwise genetic distances of CO1 sequences from 89 individuals were computed based on Kimura 2-parameter with MEGA v. 7.0.26 (Kumar et al. 2016). These comprised of eleven species, including the six new species.

Web interface species delimitation using 16S mtDNA
We carried out two more approaches of web interface species delimitation to provide more insight in our species delimitation, namely, Automatic Barcode Gap Discovery (ABGD) (http://wwwabi.snv.jussieu.fr/public/abgd/abgdweb.html) (Puillandre et al. 2012a), and Poisson Tree Processes (PTP) (http://species.h-its.org/ptp/) (Zhang et al. 2013). ABGD analysis was carried out using 16S mtDNA sequences of the "scaly group" Georissa (excluding the outgroup). The parameters were set to default. For PTP analysis, we used the 16S gene tree generated from IQ-TREE (Nguyen et al. 2014). The parameters were set to default. Both ABGD and PTP analyses were conducted using mtDNA 16S sequences and gene tree based on the available data of all studied taxa. ABGD aims to partition the species based on the barcode gap (Puillandre et al. 2012a), while PTP focuses on the branching event of a rooted phylogenetic tree (Zhang et al. 2013).

Morphology and phylogenetic analyses
Our morphological and phylogenetic studies lead us to conclude that there are at least 13 species of "scaly group" Georissa currently existing in Malaysian Borneo (for detailed morphological species descriptions, see the species treatments under the Taxonomy section). For one of these, Georissa scalinella (van Benthem-Jutting, 1966), DNA data are yet unavailable. Detailed conchological assessments of the "scaly group" show that at least two species, Georissa bauensis sp. n. and Georissa hosei Godwin-Austen, 1889, are highly variable (both intra-and inter-populationally) with regard to the "scaly" shell microsculpture characters (see Fig. 1). Due to the high inter-and intraspecific variation of these species, identification based on morphological characters alone could be problematic without prior knowledge of the shell variation within these species. Furthermore, species similar in shell habitus and scale characters, like Georissa pyrrhoderma Thompson & Dance, 1983 and Georissa sepulutensis sp. n., often have character combinations that overlap with either G. bauensis or G. hosei. Therefore, for identification of "scaly group" specimens, we found thorough conchological examination of the shells aided with molecular data is most reliable. Based on the molecular phylogenetic analyses of the "scaly group" Georissa we find multiple strongly supported monophyletic groups (bootstrap and posterior output values ranging from 89-100 and 97-100, respectively) which correspond with subtly different conchologies. In contrast, Georissa kobelti Gredler, 1902 is paraphyletic, and we treat this as a single species based on the conchological characters that support they are conspecific.

CO1 genetic divergence
Despite geographic proximity for some populations of morphologically highly similar forms, the CO1 divergence analysis shows high genetic divergences (e.g. G. bauensis vs. G. hosei, genetic divergence = 0.12). For some other species, the interspecific genetic divergence is lower, but such species may be surprisingly distinct in shell sculpture (e.g. G. hadra vs. G. muluensis, genetic divergence = 0.07). As a consequence, we have sometimes given priority to genetic distinctness, sometimes to morphological distinctness in delimiting species, which means that intraspecific diversity may vary between species. For example, we found that G. pyrrhoderma, G. hosei, and G. kobelti are the three species to have the highest intraspecific divergence (0.06, 0.06 and 0.07, respectively) compared with the rest of the "scaly group", where all other species have an intraspecific divergence equal to or lower than 0.05 (see details in Table 2). Our study reveals that within group divergences of "scaly" Georissa does not exceed 0.07 for each species, while the divergences between all species pairs exceed 0.10, with the exception of G. kinabatanganensis vs. G. sepulutensis, G. bauensis vs. G. silaburensis, G. hadra vs. G. muluensis and G. kobelti vs. G. niahensis.

Web interface species delimitation using 16S mtDNA
To test to what extent automated procedures, based on genetic data alone, could reproduce our subjective species delimitation, we carried out ABGD and PTP analyses. Table 2. Intra-and inter-specific CO1 sequence divergence of eleven species of "scaly" Georissa. ABGD recursive partition divided the "scaly group" Georissa into no more than six species at the lowest intraspecific divergence, while the highest divergence grouped all "scaly group" Georissa into a single species. The ABGD analysis further showed that partitioning into six species was due mostly to the separation of G. saulae into five different species while the rest of "scaly" Georissa were considered as a single species. This is possible due to the even higher intraspecific divergence of 16S mtDNA of G. saulae compared to the rest of "scaly group" taxa (see Suppl. material 2). While ABGD analysis underestimated the number of possible species in the "scaly group" of Georissa, PTP analysis based on maximum likelihood delimitation results devided the taxa in at least 15 possible species. The results from this species delimitation method therefore more closely match our preferred approach (in which we combined phylogenetic and morphometric assessment). The PTP analysis does, however, differ from our preferred delimitation at several crucial points. G. saulae, G. kinabatanganensis, G. hosei, G. kobelti, and G. niahensis are each split into two species, whereas the two sets of species composed of (i) G. hadra and G. muluensis, and (ii) G. bauensis and G. silaburensis, are each considered as a single species, which make another two species. Otherwise, PTP analysis resolves the same species as in our preferred resolution (see Suppl. material 3).
The results from CO1 barcoding, ABGD, and PTP analyses reveal that objective species delimitation based solely on molecular data will not be successful for "scaly group" Georissa, at least if one wishes for the taxonomy to reflect morphology as well. Since most species are allopatric, and therefore the maintenance of species barriers can usually not be tested, we present our taxonomy as a compromise, which remains to be further tested by future workers.

"Scaly group"
We here define an informal group of 13 species of Georissa from Malaysian Borneo that are characterised by one or more spiral rows of scale-like sculptures. As far as they were known at the time, our "scaly group" corresponds to Thompson and Dance's (1983) "hosei group" + "borneensis group" p.p.
Conchological description of a generalised "scaly group" representative. Protoconch. Color (in living or freshly dead specimens): yellow, orange, red or brown. Sculpture: smooth, meshed, mixed or undefined. Teleoconch. Color (in living or freshly dead specimens): yellow, orange, red or brown. First whorl: convex, rounded to flat or  angular. Subsequent whorls: convex, rounded, concave or tilted at the periphery, or flat, with well-impressed suture. Number of whorls: 2-3 ¼. Shell height (SH) (based on our conchological measurements of available studied materials stated in the methodology): 0.94-2.91 mm. Shell width (SW): 0.98-2.19 mm. Shell index (SI=SH/ SW): 0.88-1.37. Shell sculpture. Radial sculpture: either absent or present. Growth lines: weak to strong. Spiral sculpture: absent or present; if present then weakly to strongly sculpted, continuous or discontinuous. Scales: between one and four spiral rows of vertical scales (any one of which may be more or less strongly pronounced than the others); scales can be minute to broad, low to acutely projecting. Columella wall. Smooth, translucent, and covering the umbilicus region. Aperture. Shape: oval to rounded, with straight to concave or convex parietal site, palatal edge either contiguous with or removed from the body whorl. Aperture height (AH): 0.50-1.33 mm. Aperture width (AW): 0.69-1.48 mm. Aperture index (AI=AH/AW): 0.65-1.02. Peristome. Simple, thickened inside, sharp toward the edge of the aperture. Operculum. Oval to rounded, with a peg facing inward, inner surface of the operculum has a small craterlike hole. Peg: straight or curved. The shell measurement of all measured "scaly group" Georissa are summarised in Suppl. material 4.
Anatomy. Haase and Schilthuizen (2007) described the anatomy of two closely related Georissa, viz. G. saulae and G. filiasaulae, and noted interspecific differences in radula, genital anatomy. Anatomical details of other "scaly group" representatives will be the focus of future studies and are not included in the present review.
Habitat and ecology. Members of the "scaly group" of Georissa live on limestone rocks, especially in wet and shaded environments. They are also found at lower density on dry limestone rocks, and occasionally on the limestone walls in cave systems (Haase and Schilthuizen 2007).
Distribution. There are at least nine species of this group distributed in Sarawak, and another four are distributed in Sabah (see Figures 3 and 4). In the distribution maps, we combined the geographical coordinates of each species from the known previous fieldwork locations and the available data from the collection repositories. The distribution of "scaly group" Georissa was assigned based on the available locality data from the collection from NHMUK, RMNH, ZMA, BOR, ZMU, and JJV. Localities may contain Malay words, namely: Batu = rock; Bukit = hill; Gua = cave; Gunung = mountain. We provide two distribution maps (Figs 3 and 4) to avoid overlapping of species that co-occur at the same or nearby locations.
In the following systematic descriptions of "scaly" Georissa, the species are arranged based on the molecular phylogeny. Georissa scalinella (van Benthem-Jutting, 1966), for which no genetic data are available, is placed at the top of the list.
For the stacked images of the "scaly" Georissa (Figs 5-17A-C), we decided not to remove the periostracum layers of the shells to retain the morphological characters of each species.
Since we needed fresh material to connect the morphology and molecular phylogenetics, we confined our study to Malaysian part of Borneo. We are aware that there might be species or populations in other parts of Borneo (Kalimantan, Indonesian  Borneo and Brunei) which belong inside the "scaly group". However, we hope that our study will stimulate colleagues that study Georissa in Kalimantan or Brunei to compare their material with our analysis.

Georissa scalinella (van Benthem-Jutting, 1966)
Hydrocena scalinella van Benthem-Jutting, 1966: 39, fig. 1 Cross diagnosis. Georissa scalinella has a series of scales at the shoulder. In habitus and scale characters, it resembles G. pyrrhoderma from Gunung Silabur, Sarawak. The angular shoulder and small scale-like nodular structure at the intersection of strong spiral ribbings and growth lines are diagnostic for G. scalinella.
Distribution. Known only from the type locality, Teck Guan Estate, Lahad Datu, Sabah, and also reported by Phung et al. (2017) at Pulau Tiga, Sandakan, Sabah. However, this may also refer to one of the other "scaly group" species from Sabah.
Cross diagnosis. Georissa saulae possesses clear diagnostic shell characters for distinction from other "scaly" Georissa species. G. saulae lacks a clear formation of spiral ribbing: although the spiral arrangement of the scales gives the impression of spiral sculpture, no underlying ribs are discernable. G. scalinella, G. kinabatanganensis, and G. hosei, on the other hand, have clear diagnostic spiral ribs. The shell whorls of G. saulae are broad but not as rapidly expanding as in G. hosei, G. scalinella or G. kinabatanganensis. It can also be distinguished from G. scalinella and G. hosei on the basis of a more elongate-conical shell shape and the aperture shape that is more rounded rather than oval.
Distribution. The type locality of Georissa saulae is Laying cave, in the Crocker Range, Keningau, Sabah (a misspelling of Laing cave). Otherwise known from limestone outcrops in Sabah's interior, viz., Simbaluyon, Sinobang, Sanaron, and Pungiton, and also has been recorded from Mahua, Sabah, which is not a limestone area. Phung et al. (2017) also report it from Pulau Tiga, Sabah. Molecular analysis. ML and Bayesian analyses show Georissa saulae (16S: n = 11) as a monophyletic group with 100% BS and 100% PP. Schilthuizen et al. (2012) reported that G. saulae is a paraphyletic group from which emerges the cave-dwelling species G. filiasaulae (Haase and Schilthuizen 2007), a fully unsculptured species that was not included in the present study. G. saulae + G. filiasaulae are sister to all other species in the "scaly group" (unpublished data).
Discussion. Georissa saulae was initially described as Hydrocena saulae van Benthem-Jutting, 1966, then assigned to the genus Georissa by Thompson and Dance (1983). Thompson and Dance (1983) compared G. saulae with G. scalinella, and even suggested G. saulae might be a subspecies. In contrast, we find that G. saulae is a proper species with very distinct conchological characters, especially the presence of radial ribs on the shell, which makes it easy to identify. In some specimens from the entrance of the Batu Sanaron cave system, the vertical scales are spaced, and radial sculpture is weak. Such individuals presumably represent the hybrid zone with the cave-dwelling G. filiasaulae Schilthuizen 2007, Schilthuizen et al. 2012).
Cross diagnosis. Georissa hosei has a diagnostic smooth protoconch. It possesses similar shell habitus and scale characters as G. sepulutensis, G. pyrrhoderma, and G. kobelti. However, the scales of G. hosei are rarely developed into large and acutely projected scales.
Distribution. Known from Gunung Liak/Padang and Bukit Siboyuh at Kampung Skiat Baru, Jambusan, and Bukit Tongak, in the area of Bau, which is close to Jambusan. Molecular analysis. ML and Bayesian analyses shows that all G. hosei individuals (16S: n = 21; CO1: n = 11) group together in one clade with 100% BS and 100% PP, which is the sister group of all other "scaly group" species, except G. saulae.
Discussion. Godwin-Austen (1889), when he described the species, mentioned that the sides of the spire (whorls) are flat, which we find to be the case for the first whorl in our material (as well as in the lectotype). The exact type locality was not specified, but Smith (1893) reported that the specimens of G. hosei described by Godwin-Austen (1889) were from Jambusan, Sarawak. It has to be noted that G. hosei is highly variable in shell shape and sculpture, even within a local population. For example, material we collected at Gunung Liak/Padang have anything between two and four series of broad and low scales. Material from Bukit Tongak has three to four spiral threads with scales.
Material from Bukit Siboyuh, finally, is brighter in color (orange), with only one or two spiral series of scales. These three limestone outcrops are all within the area of not more than 10 km radius. Thompson and Dance (1983) noted that G. hosei is widely distributed in Sarawak, and they give Baram, Marudi, Niah, Tatau, and Bukit Sarang as localities. However, as we elaborate in this paper, many of these populations are not conspecific with G. hosei. For example, the image of "G. hosei" provided by Thompson and Dance (1983) -UF 35919, from Batu Gading, Baram, appears conspecific to G. kobelti. Also, their "G. hosei" from Bukit Sarang we here describe as a G. anyiensis sp. n. Etymology. Named after the hill Bukit Anyi at Bukit Sarang, Bintulu, Sarawak, Malaysia, the type locality.

Georissa hadra Thompson & Dance, 1983
Georissa hadra Thompson & Dance, 1983: 115-116, fig. 32, 43-46. Type locality. Butik Besungai, a small limestone hill 0.5 miles southwest of Batu Gading, and about 4 miles northeast of Long Lama, Baram Valley, Fourth Division, Sarawak. 03°52'N, 114°25'E. Butik = a misspelling of Bukit, a local name for hill. Description. Protoconch. Color: orange. Sculpture pattern: meshed -rounded to ellipsoidal or undefined mesh shape. Mesh width: 12-24 µm. Teleoconch. Color: orange. First whorl: with a distinct shoulder (provided with a series of minuscule scales), above the shoulder flat and tapering towards the suture, below the shoulder flat and cylindrical. Subsequent whorls: distinctly scalariform, with three separate aspects separated by two or more main spiral series of scales: above the uppermost spiral series gently curved towards the suture; in between both spiral series flat and cylindrical; below the lowest spiral series abruptly narrowed towards the deeply impressed suture (on the final whorl these three aspects fuse, forming a uniformly rounded impression). SH: 2.61-2.91 mm, SW: 2.05-2.19 mm, SI: 1.21-1.37. Total number of whorls: 2 ¾-3 ¼. Shell sculpture. Radial sculpture: absent, but with strong and unevenly layered growth lines. Spiral sculpture: present, weakly sculpted, continuous to discontinuous. Scales: two to four irregularly spaced series of low to high, and minute to broad diagonal scales, densely spaced, the first scale series always the strongest, weaker series appearing later at the spire. Aperture. Shape: rounded, with a tilt below the palatal side. Basal side: rounded, angular at the columellar region. Parietal side: straight to curved. AH: 1.11-1.33 mm, AW: 1.32-1.48 mm, AI: 0.83-1.01.
Cross diagnosis. Georissa hadra has scales which are densely arranged, unlike G. scalinella, G. hosei, G. muluensis, G. anyiensis, and G. kobelti, which have more widely spaced scales. In shell shape, G. hadra is similar to the later three species but larger and more distinctly scalariform. G. hadra is similar in size to G. niahensis, but it has a more slender habitus and a more rounded periphery.
Distribution. The type locality for G. hadra is Bukit Besungai, Baram, Sarawak. We also obtained it at Mulu, Sarawak. Currently, therefore, the known distribution range is restricted to Mulu and Baram. Molecular analysis. ML and Bayesian analyses retrieve G. hadra (16S: n = 4; CO1: n = 4) as a single clade with 89% BS and 100% PP, sister to G. muluensis.

Georissa kobelti
Description. Protoconch. Color: orange to red. Sculpture: meshed -semi-oval mesh shape. Mesh width: 11-22 µm. Teleoconch. Color: ranging from red to yellow. First whorl: convex to rounded. Subsequent whorls: convex to rounded. SH: 1.75-2.11 mm, SW: 1.48-1.75 mm, SI: 1.18-1.28. Total number of whorls: 2 ¾-3. Shell sculpture. Radial sculpture: absent, only weak growth lines. Spiral sculpture: present with thin but strongly continuous spiral ribs, forming small acute scales near the suture. Scales: three to four spiral rows of tilted, nearly vertical scales, the upper series stronger than the lower ones, scale prominence ranging from high to low and from small and acute to broadly sculpted and ear-like. Scales are regularly spaced, as are the scale series themselves. Aperture. Shape: rounded to oval. Basal side: rounded, angular before the columellar region. Parietal side: curved. AH: 0.82-1.04 mm, AW: 1.02-1.17 mm, AI: 0.71-0.90.
Cross diagnosis. The image of the G. kobelti lectotype by Zilch (1973) does not provide detailed information about the scale characters of G. kobelti as compared to the images of the individual from UF provided by Thompson and Dance (1983), which clearly shows the diagnostic characters of the ear-like scale pattern of this species. In shell habitus, G. kobelti is similar to some populations of G. anyiensis, G. saulae, and G. hosei, but these species differ from G. kobelti by the pattern of their diagonal scales.
Distribution. The lectotype in Senckenberg (SMF 215893a) was obtained from an unspecified location. As far as known, the species is restricted to the area of Niah to Baram, northern Sarawak. Thompson and Dance (1983) also stated that they examined this species from Beluru, which is located between Niah and Baram.
Description. Protoconch. Color: red. Sculpture pattern: smooth and meshed -ellipsoid to irregular mesh shape. Mesh width: 12-19 µm. Teleoconch. Color: orange to red. First whorl: curved above the shoulder, flat and cylindrical below the shoulder. Subsequent whorls: convex, angular at the periphery. SH: 1.81-2.53 mm, SW: 1.51-1.99 mm, SI: 1.10-1.29. Total number of whorls: 3-3 ¼. Shell sculpture. Radial sculpture: absent, only strong and unevenly layered growth lines. Spiral sculpture: present, strongly sculpted, continuous to discontinuous, well defined from the first whorl all the way to the peristome. Scales: a single spiral series of low and minute acute scales, regularly spaced at the first whorl, but weaker, grading to imperceptible on the body whorl. Aperture. Shape: rounded. Basal side: rounded, angular at the columellar region. Parietal side: straight to curved. AH: 0.85-1.24 mm, AW: 0.92-1.27 mm, AI: 0.83-1.02.
Cross diagnosis. Georissa niahensis has a distinctive single series of small scales on the whorl shoulder, close to the suture. G. niahensis is one of the largest Bornean Georissa, in shell size only matched by G. hadra (which, however, is more slender, angular at the shoulder and has a flat to slightly rounded whorls). In general shell shape, G. niahensis is closest to G. kobelti, but the latter species is more rounded, while G. niahensis has a distinctly convex periphery.
Distribution. Known to occur only at Niah, Sarawak. Molecular analysis. ML and Bayesian analyses of G. niahensis (16S: n = 8; CO1: n = 7) showed that all G. niahensis specimens form one clade with 100% BS and 100% PP. The sister group is the G. kobelti population from Baram (G. kobelti is paraphyletic).
Discussion. Both Godwin-Austen (1889) and Thompson and Dance (1983) did not mention anything about the small scale-like nodules close to the suture of G. niahensis. Godwin-Austen (1889): "Shell elongately conoid, solid, imperforate; sculpture a very in-distinct, ill-defined spiral liration, about 20 on the penultimate whorl, upon a rough surface crossed by transverse lines of growth; color ruddy ochre; spire high; apex pointed, finely papillated, minutely lirate; suture impressed; whorls 4 ½ convex; aperture oval, oblique; peristome simple, acute below; columellar margin straight". Thompson and Dance (1983): "G. niahensis is similar in sculpture to G. williamsi but is much larger. G. niahensis also shows similarities to the hosei group in the depth of the suture and the relatively rapid expanding whorls, but it lacks the node-like sculpture found among species of that group." The scales are relatively small which are not very conspicuous among the strong growth lines, and this is the reason why in the previous description of the species the scale characters were lacking. Thompson and Dance (1983)  . Shell sculpture. Radial sculpture: absent or weak to strong growth lines. Spiral sculpture: present, thin but strongly sculpted, continuous ribs, more prominent at the periphery. Scales: two to six or more randomly sculpted series of low and broad horizontal scales, or else acute horizontal nodules on the spiral sculpture, scale series irregularly spaced, which series is the most prominent is not consistent across individuals. Aperture. Shape: rounded. Basal side: rounded, angular at the columellar region. Parietal side: straight, palatal edge attached to slightly removed from the body whorl. AH: 0.95-1.09 mm, AW: 1.00-1.17 mm, AI: 0.92-0.99. Holotype dimension. SH: 1.68 mm, SW: 1.53 mm, AH: 0.95 mm, AW: 1.09 mm.
Cross diagnosis. The shell shape of G. silaburensis is distinct compared to other "scaly group" Georissa. It has rapid shell expansion like G. hosei and G. scalinella, but G. silaburensis has a different sculpture, consisting of horizontal, rather than vertical or diagonal scales. In addition, the whorls are rounded and convex, with the aperture almost circular, close to G. saulae.
Distribution. Known from the inside of the cave system of Gunung Silabur, Serian, Sarawak.
Molecular analysis. ML and Bayesian analyses show that the individuals of G. silaburensis (16S: n = 10; CO1: n = 9) form one clade with 95% BS and 98% PP, the sister group of G. bauensis.
Discussion. Georissa silaburensis was only found inside the cave entrance, with water flowing from the cave roof, and approximately less than 50% light penetration. In shell shape and reduced sculpture, it resembles another cave specialist, G. filiasaulae.  Etymology. Named after the district of Bau, Sarawak, Malaysia, where the type locality Wind Cave Nature Reserve is located.
Cross diagnosis. Georissa pyrrhoderma has a shell habitus that is similar to G. kobelti, G. hosei, and G. sepulutensis. The latter two species are high variable and are morphologically, especially in sculpture, closely related to G. pyrrhoderma. Therefore, G. pyrrhoderma is nearly indistinguishable from certain forms of these other species.
Discussion. In the original description, Thompson and Dance (1983) did not compare G. pyrrhoderma with members of their hosei-group (which our molecular analyses show it belongs in). Instead, they considered it allied to G. borneensis. Possibly this misalignment was caused by the fact that the type specimens appear to lack the series of scales that is present on most of the specimens we collected. Nonetheless, given the restricted range of collection localities at Gunung Silabur and the degree of variability in our material, we consider our and Thompson  Etymology. Named after the district of Kinabatangan, Sabah, Malaysia, where the type locality Bukit Keruak is located.
Description. Protoconch. Color: orange. Sculpture pattern: smooth to meshedrounded to undefined mesh pattern. Mesh width: 14-21 µm. Teleoconch. Color: orange. First whorl: flat and angular at the shoulder. Subsequent whorls: angular, slightly rounded at the periphery, with number of whorls: 2-2 ¼. SH: 1.00-1.32 mm, SW: 1.13-1.37 mm, SI: 0.85-0.99. Shell sculpture. Radial sculpture: absent, only weak to strong growth lines are visible. Spiral sculpture: present, and strongly sculpted, with continuous to discontinuous ribbings. Scales: two series of diagonal vertical scales, widely spaced in between, both series are strongly sculpted, broad, and the scales are regularly placed. Aperture. Shape: oval. Basal side: rounded, angular at the columellar region. Parietal side: straight, palatal edge attached to the body whorl. AH: 0.54-0.66 mm, AW: 0.75-0.86 mm, AI: 0.65-0.80. Holotype dimension. SH: 1.00 mm, SW: 1.18 mm, AH: 0.54 mm, AW: 0.78 mm. Cross diagnosis. Georissa kinabatanganensis has less variation in shell sculpture compared with G. hosei and G. scalinella. G. kinabatanganensis has two series of acutely projected scales on the whorls. In some cases, the second scale series is weaker than the first, and creates a series of nodular structures at the periphery. Often the shell is wider than high, which gives it a flattened appearance. In addition, G. kinabatanganensis has widely spaced between the scale series, similar to G. muluensis. Molecular analysis. ML and Bayesian analyses show G. sepulutensis (16S: n = 10; CO1: n = 2) as two clades with 93% BS and 97% PP, and as the sister species to G. kinabatanganensis sp. n.
Discussion. Georissa sepulutensis and G. kinabatanganensis were previously included in G. scalinella (van Benthem-Jutting, 1966). Based on the genetic and morphological distinctness, we here consider them as separate species.