A NEW SPECIES OF BROTIA H. ADAMS, 1866 (CAENOGASTROPODA: CERITHIOIDEA: PACHYCHILIDAE) FRANK KÖHLER & MATTHIAS GLAUBRECHT Museum für Naturkunde, Institute of Systematic Zoology, Humboldt University, Invalidenstr. 43, D-10115 Berlin, Germany (Received 13 January 2002; accepted 8 April 2002)
ABSTRACT A new species, Brotia praetermissa, is described from Borneo. The type material was found unidentified in the spirit collection of the Natural History Museum, London. It was collected by A. Everett in the nineteenth century. Using morphological characters, the new species is affiliated with the Brotia pagodula species group. Representatives of this group can easily be recognized by the wrinkled apical shell of their protoconch. The species described herein is the only known representative of the likely monophyletic B. pagodula group in Borneo, while all other Brotia species known from this island are assigned to the Brotia testudinaria group. This finding renders it most likely that Borneo has been colonized twice by species of the genus Brotia, by the ancestor of B. praetermissa and that of the Brotia testudinaria group.
INTRODUCTION Brotia H. Adams, 1866 is a genus of southeast Asian freshwater gastropods typically inhabiting mountain streams and rivers in tropical forests. The distribution of these viviparous snails ranges from northeast India to the Greater Sunda Islands of Sumatra, Java and Borneo, as well as to southern China. Knowledge of these snails still is scanty and little is known concerning details of their ecology and evolution. Recently, the first attempt at a more reliable phylogenetic framework was presented, based solely on morphological data (Köhler & Glaubrecht, 2001). This suggested the differentiation of three groups among the species previously attributed to Brotia in a wider sense and, in addition, that two of these groups should be considered as separate genera. Consequently, all species from Sulawesi have recently been transferred to Tylomelania Sarasin & Sarasin, 1897 (see Rintelen & Glaubrecht, 2002), while for the species endemic to the Philippines the new genus Jagora has been described (Köhler & Glaubrecht, in press). These three genera can be discriminated, among other features, by means of their reproductive anatomy, including different brooding morphologies (Rintelen & Glaubrecht, 1999, 2002; Köhler, Rintelen & Glaubrecht, 2000; Köhler & Glaubrecht, 2001, in press). Furthermore, among the species remaining in Brotia, two subgroups can be distinguished, which are characterized most strikingly by different protoconch morphology. While a number of species, among them the type species B. pagodula (Gould, 1847), exhibiting a typically wrinkled apical shell surface are united under the Brotia pagodula species group, those with a smooth apical shell have been placed in the Brotia testudinaria species group (see Köhler & Glaubrecht, 2001). However, no autapomorphic character has so far been identified to establish a monophyletic status for the latter group. In order to investigate the phylogenetic relationships within and between these species groups and genera, continuing studies integrating additional morphological and especially molecular genetic data are necessary. Therefore, until a robust phylogeny of Brotia is established, we will refrain from further taxonomic decisions. The current systematic and taxonomic knowledge of Brotia and the related Southeast Asian pachychilid genera is briefly summarized by Köhler & Glaubrecht (2002a).
MATERIAL AND METHODS This description is based on material deposited in the spirit collection of the Natural History Museum, London (BMNH), Correspondence: F. Köhler; e-mail:
[email protected]
J. Moll. Stud. (2002) 68: 353–357
which is preserved in 70% ethanol. Dimensions of the shell were measured with a calliper to 0.1 mm. The shell height is the maximum dimension parallel to the axis of coiling, the breadth the maximum dimension perpendicular to height. The length of the aperture is the greatest length from the junction of the outer lip with the penultimate whorl to the anterior lip, the width of the aperture the greatest length perpendicular to the length. The height of the body whorl is the maximum dimension from the lower margin of the aperture to the upper suture delimiting the first whorl. Anatomy was studied using a stereo microscope. The extracted radula was cleaned by soaking in 1% hypochlorite solution at room temperature for about 5 min and rinsing in distilled water (see Reid, 1986: 5). The radula was mounted on an aluminium stub using adhesive tape and coated with gold for examination with a scanning electron microscope. Some juvenile shells were taken from the brood pouch, cleaned by ultrasound and mounted for SEM as described above.
SYSTEMATIC DESCRIPTION
Cerithioidea Férussac, 1822 Pachychilidae Fischer & Crosse, 1892 Brotia H. Adams, 1866 Brotia praetermissa new species (Figs 1-5) Types: Holotype (male) BMNH 20010482/A (Fig. 1A): from ‘Borneo’ (label: ‘Melania No. 81, Borneo, leg. Esq. Everett, Godw.-Austen Colln Acc. No. 1830’). Three paratypes BMNH 20010482/B, two of them with broken shells. Remarks: The type locality could not be precisely defined. It seems convincing that Borneo is the correct collecting locality as A. Everett did spend time in Borneo, where he made extensive collections of mainly land snails. He also was encouraged by Godwin-Austen to preserve specimens in spirit whenever possible. While descriptions on the land snails collected by Everett were published (Godwin-Austen, 1889; Collinge & Godwin-Austen, 1895), the promised work on the non-marine aquatic taxa never appeared (F. Naggs, personal communication). The number ‘81’ was given probably by Godwin-Austen and is his list number of Everett’s material. Etymology: The material of this species was collected probably in the 1880s and has been kept unidentified for more than a cen© The Malacological Society of London 2002
F. KÖHLER & M. GLAUBRECHT Table 1. Measurements of the holotype and the unbroken paratype specimen (mm). Aperture
Aperture
Body
Number
Height
Breadth
length
width
whorl
of whorls
Holotype
58.4
22.2
19.0
11.5
29.1
8
Paratype
58.0
22.3
19.2
11.3
28.0
8
relatively small, round, multispiral operculum; inner and outer marginal teeth of radula with a very broad oval main tooth, only some outer marginals with an accessory cusp at inner side. Shell (Fig. 1): Highly turreted with about eight stepped whorls, covered by thick calcareous deposit. Spire eroded at tip, whorls separated by relatively deep suture. Sculpture of six strong spiral ridges that are most prominent on base, and one or two spiral rows of spiny nodules that are most prominent on second whorl. Early whorls of teleoconch smooth or sculptured by inconspicuous axial ribs only. Colour brown to yellowish brown (probably leached due to preservation in ethanol). Shell dimensions are given in Table 1.
Figure 1. Shells of Brotia praetermissa n. sp. A. Holotype (BMNH 20010482/A). B. One of four paratypes (BMNH 20010482/B). Scale bar 10 mm.
Embryonic shells (Fig. 2): Juveniles within brood pouch all of same size, about 4 mm in height. Shells completely calcified, comprising about 3.5 whorls. Juvenile shell turreted with flattened whorls, shell texture smooth, sculptured only by faint spiral lines and regular growth lines. Apical whorl with irregularly wrinkled sculpture delimited by sharp transition after about two thirds of first whorl.
tury in the spirit collection of the BMNH. Since it was obviously overlooked by previous researchers, it is called herein Brotia praetermissa (Latin, the overlooked Brotia). Diagnosis: Highly turreted shell with stepped whorls, conspicuous spiral ridges, and one or two spiral rows of spiny nodules; a
Figure 2. SEM images of a juvenile shell removed from the brood pouch of one of the paratypes of Brotia praetermissa. A. Frontal view. B. Apical view showing the wrinkled shell sculpture of the apical whorl. Scale bars 1 mm.
354
NEW SPECIES OF BROTIA 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 20 1 2 3 4 5 6 7 8 9 30 1 2 3 4 5 6 7 8 9 40 1 2 3 4 5 6 7 8 9 50 1 2 3 4 5 6 7 8 9 60 1 2 3 4 5 6 7 8
me
hd tn
sn Figure 3. Morphological features of one of the paratypes of Brotia praetermissa. A. Operculum. B. Stomach morphology. Abbreviations: cf, crescent fold; dg, digestive gland duct; gp, gastric pad; gs, gastric shield; mf, marginal fold; os, opening to the style sac; sa, sorting area; t1, major typhlosole; t2, minor typhlosole. Scale bars 5 mm.
cm
Operculum (Fig. 3A): Round, multispiral, with central nucleus and up to 10 whorls. Diameter considerably smaller than aperture.
gg
ft
Figure 4. Photograph of the headfoot of a paratype of Brotia praetermissa. Scale bar 10 mm. Abbreviations: cm, columellar muscle; hd, head; gg, genital groove; ft, foot; me, mantle edge; sn, snout; tn, tentacle.
External morphology (Fig. 4): Animal brown with light to yellowish brown patches. Head with two cephalic tentacles, each with a tiny eye at the outer base, a broad and furrowed snout, and a genital groove at the right side running downwards from anterior end of pallial gonoduct. Mantle cavity occupying about two-thirds of first whorl. Osphradium delicate, forming a narrow undulating ridge adjacent to anterior part of ctenidium. Ctenidium large, broad and tapers posteriorly, it begins shortly behind the mantle edge, extending posteriorly almost entire length of mantle cavity. Hypobranchial gland inconspicuous, lying adjacent to large and wide rectum. Anus located well behind mantle edge. Mantle edge smooth. Columellar muscle broad and well developed.
forming a deep sperm gutter that gives rise to a simple and sac-like spermatophore bursa. Due to poor preservation, a more detailed description is not possible. Comparison with other congeneric species: The new species B. praetermissa has the turreted shell with a wide, oval and basally produced aperture typical of Brotia, as exhibited, for example, in B. costula and B. episcopalis (see Köhler & Glaubrecht, 2001). It also shares with all other known species of Brotia the presence of basal spiral ridges and a round, multispiral operculum, the general morphology of the radula and the soft body. More important, the morphological details of the pallial oviduct of the females and the wrinkled structure of the apical whorl of the juvenile shell are very similar to features found in B. pagodula, the type species of the genus (Köhler & Glaubrecht, 2001).
Radula (Fig. 5): Taenioglossate; ribbon robust, about 2 cm long with 120 rows of teeth. Central tooth with one main cusp flanked on each side by two smaller ones that taper in size and a well developed glabella with a rounded basal margin; anterior rim of central tooth slightly concave, flanked by the two slightly excavated lateral corners, basal rim rounded. Lateral tooth with a major cusp flanked by two accessory cusps on each side, a well developed glabella and a comparatively long lateral extension. Inner marginal tooth with only one very broad and spatulashaped cusp, while some of outer marginals in addition possess an accessory cusp at the inner side (Fig. 5D). Both inner and outer marginals curved or knee-shaped, the outer ones with a flange at their exterior side.
DISCUSSION Recently, it has been demonstrated that Brotia and a number of other southeast Asian gastropods are members of the Pachychilidae, a family of freshwater snails with a worldwide distribution in the tropics (Glaubrecht, 1999, 2000; Köhler & Glaubrecht, 2001). This classification is based on a number of peculiar characteristics that represent probable synapomorphies as identified by Strong & Glaubrecht (1999). Additional support for this view is gained from molecular genetic analyses (F. Köhler, T. von Rintelen, A. Meyer & M. Glaubrecht, unpublished data). The diagnostic characters typical for pachychilids, i.e. certain features of the stomach (Fig. 2B) and the radula (Fig. 5; for more details see Köhler & Glaubrecht, 2001), have also been found in B. praetermissa. The new species shares several features with Brotia pagodula, type species of the genus, as well as with other representatives of the genus. These features are the more or less turreted shell sculptured by spiral ridges at least at the base, an oval and basally well rounded or even produced aperture, a round to ovate and multispiral operculum with a more or less central nucleus, a subhaemocoelic brood pouch located well behind the buccal mass, the morphology of the pallial oviduct (i.e. a long, deep, ciliated
Alimentary system (Fig. 3B): Stomach with crystalline style, the style sac communicating with the intestine, as major and minor typhlosole are not fused to each other, a large gastric pad supporting a cuticular gastric shield, a complex sorting area comprising two crescentic septate thickenings bounded by two crescent regularly laminated areas, a marginal fold, a simple opening to the digestive gland duct, and inner and outer crescentic folds situated posterior to that opening. Reproductive biology: Females with subhaemocoelic brood pouch located well behind buccal mass and occupying a large part of visceral cavity; one animal containing 18 shelled juveniles. Pallial oviduct comprises two laminae, with median lamina 355
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Figure 5. SEM images of the radula of one of the paratypes of Brotia praetermissa. A. Radula segment viewed from above. B. Detail of the same radula viewed from above. C. Lateral view at an angle of about 45 from above. D. Dorsal view at an angle of about 45 from above. Scale bars 0.1 mm.
easily be distinguished from both species by its round and relatively small operculum and the presence of a subhaemocoelic brood pouch, which is lacking in the others. According to current knowledge, the new species is the only representative of the Brotia pagodula group occurring in Borneo. All other Brotia species known from Borneo, e. g. Brotia infracostata (Mousson, 1848), B. clavaeformis (Brot, 1874) and B. pageli (Thiele, 1908), have protoconchs with a smooth apical whorl, a characteristic of the Brotia testudinaria species group (see Köhler & Glaubrecht, 2001). This grouping comprises species with a distribution to the east of Sundaland, i.e. Java, Borneo and IndoChina, but apparently not extending to the west, i.e. to western and northern Thailand, Myanmar or India. Although the monophyly of the latter species group still needs to be tested, the occurrence of a representative of the Brotia pagodula group on Borneo renders it most likely that this
sperm gutter and a simple sac-like spermatophore bursa), and a conspicuously wrinkled apical sculpture of the protoconch (Köhler & Glaubrecht, 2001). Based on the wrinkled apex of the juvenile shell and the characteristic morphology of the pallial oviduct, B. praetermissa is affiliated with the Brotia pagodula species group, a probable monophyletic clade comprising a number of species from the southeast Asian mainland and Sumatra. From other species of this species group, B. praetermissa can be distinguished most easily by the highly turreted spire with stepped whorls, the presence of one or two spiral rows of spiny nodules and its relatively small, round operculum. The shell of B. praetermissa is similar also to that of Jagora asperata (Lamarck, 1822) and J. dactylus (I. Lea & H.C. Lea, 1850) from the Philippines (for a detailed description of Jagora see Köhler & Glaubrecht, in press). However, B. praetermissa can 356
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island has been colonized at least twice independently by Brotia species, by an ancestor of B. praetermissa and by the representatives of the Brotia testudinaria group. The thick inorganic layer covering the shells of B. praetermissa is calcareous, formed by precipitation of calcium carbonate, and thus provides evidence that the animals lived in a stream running on a limestone substrate. This has also been found in some other species of Brotia, for example, in museum specimens of B. henriettae (Gray, 1834) and in material collected during our own field collections in southeast Asia. The frequent presence of such calcareous layers in other Brotia species reflects their affinity for calcium carbonaterich waters. This may limit the geographical distribution of some Brotia species.
GODWIN-AUSTEN, H.H. 1989. On a collection of land-shells made in Borneo by Mr A. Everett, with description of supposed new species. Proceedings of the Zoological Society of London, 1889: 332–355. KÖHLER, F. & GLAUBRECHT, M. 2001. Toward a systematic revision of the Southeast Asian freshwater gastropod Brotia H. Adams, 1866 (Cerithioidea: Pachychilidae): an account of species from around the South China Sea. Journal of Molluscan Studies, 67: 281–318. KÖHLER, F. & GLAUBRECHT, M. 2002a. Annotated catalogue of the nominal taxa of Southeast Asian freshwater gastropods, family Pachychilidae Troschel, 1857 (Mollusca: Caenogastropoda: Cerithioidea), with an evaluation of the types. Mitteilungen aus dem Zoologischen Museum, Berlin, 78: 121–156. KÖHLER, F. & GLAUBRECHT, M. in press. Morphology, reproductive biology and molecular genetics of ovoviviparous freshwater gastropods (Cerithioidea: Pachychilidae) from the Philippines, with description of the new genus Jagora. Zoologica Scripta. KÖHLER, F., RINTELEN, T. VON & GLAUBRECHT, M. 2000. Morphology, molecules and Wallacean Biogeography. The case study of the Southeast Asian freshwater gastropod Brotia (Cerithioidea: Pachychilidae). In: Abstracts of the International Symposium Biogeography of SE Asia 2000 (Jong, R. de, ed.), 51–52. Nationaal Natuurhistorisch Museum, Leiden. REID, D.G. 1986. The littorinid molluscs of mangrove forests in the IndoPacific region. The genus Littoraria. British Museum (Natural History), London. RINTELEN, T. VON & GLAUBRECHT, M. 1999. On the reproductive anatomy of freshwater gastropods of the genera Brotia H. Adams, 1866 and Tylomelania Sarasin & Sarasin, 1897 in the central lakes on Sulawesi, Indonesia (Cerithioidea: Melanatriidae). Courier Forschungsinstitut Senckenberg, 125: 163–170. RINTELEN, T. VON & GLAUBRECHT, M. 2002. New discoveries in old lakes: three new species of Tylomelania Sarasin & Sarasin, 1897 (Gastropoda: Cerithioidea: Pachychilidae) from the Malili lake system on Sulawesi, Indonesia. Journal of Molluscan Studies, in press. STRONG, E.E. & GLAUBRECHT, M. 1999. Tapping the unexplored: midgut morphology in cerithioidean gastropods (Caenogastropoda)—preliminary results and implications for phylogenetic analysis. In: Abstracts of the American Malacological Society Meeting, 53–54. American Malacological Society, Pittsburgh.
ACKNOWLEDGEMENTS We are most grateful to Fred Naggs and Joan Pickering (Natural History Museum, London) for making the material available for this study. Fred Naggs also helped by providing an overview of Everett’s collecting activities. SEM work was done during a visit to the Natural History Museum in 1999, which was funded by the ‘Bioresource’ programme of the EU. The work of the first author is funded through a postgraduate scholarship of the Konrad-Adenauer-Stiftung, Germany.
REFERENCES COLLINGE, W.E. & GODWIN-AUSTEN, H.H. 1895. On the structure and affinities of some new species of molluscs from Borneo. Proceedings of the Zoological Society of London, 1895: 241–250. GLAUBRECHT, M. 1999. Systematics and the evolution of viviparity in tropical freshwater gastropods (Cerithioidea: Thiaridae sensu lato)—an overview. Courier Forschungsinstitut Senckenberg, 125: 91–96. GLAUBRECHT, M. 2000. A look back in time. Toward an historical biogeography as a synthesis of systematic and geological patterns outlined with freshwater gastropods. Zoology, 102: 127–147.
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