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Arnhemtrachia ramingining: a new genus and species of land snail from Arnhem Land, Australia (Stylommatophora: Camaenidae) a
Frank Köhler & Francesco Criscione
a
a
Australian Museum , 6 College Street, Sydney , NSW , 2010 , Australia Published online: 02 May 2013.
To cite this article: Frank Köhler & Francesco Criscione (2013): Arnhemtrachia ramingining: a new genus and species of land snail from Arnhem Land, Australia (Stylommatophora: Camaenidae), Molluscan Research, 33:2, 110-115 To link to this article: http://dx.doi.org/10.1080/13235818.2013.782792
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Molluscan Research, 2013 Vol. 33, No. 2, 110–115, http://dx.doi.org/10.1080/13235818.2013.782792
Arnhemtrachia ramingining: a new genus and species of land snail from Arnhem Land, Australia (Stylommatophora: Camaenidae) Frank Köhler∗ and Francesco Criscione Australian Museum, 6 College Street, Sydney, NSW 2010, Australia
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(Received 26 September 2012; final version received 1 February 2013 ) The new, monotypic camaenid genus Arnhemtrachia is described for the new species Arnhemtrachia ramingining from Ramingining, Arnhem Land, Northern Territory, Australia with additional records from the Gove Peninsula in eastern Arnhem Land. This camaenid is characterised by a combination of distinct morphological features, such as a small, discoidal, keeled shell with regular axial ribs, open umbilicus and simple, rounded aperture as well as a reproductive system with a long epiphallus possessing a long flagellum and absence of a penial sheath, with a flap on the penial wall which transverses longitudinal pilasters, and a long, simple bursa copulatrix. Based on comparative morphology, Arnhemtrachia reveals affinities with Trozena morata Iredale, 1838 from NE Queensland. Keywords: Helicoidea; Pulmonata; taxonomy; Northern Territory; Australian Monsoon Tropics; morphology; anatomy
Introduction Recent decades have seen an impressive advance in the systematic study of Australian land snails, in particular of the family Camaenidae. Large surveys in Western Australia provided the foundation for the hallmark works of Alan Solem, who comprehensively revised most camaenid groups from the western part of the continent and described hundreds of new taxa (Solem 1979, 1981a, 1981b, 1984, 1985, 1988a, 1988b, 1992, 1993, 1997). The cataloguing of Western Australian camaenids has since been continued resulting in the description of an additional 118 species and 6 genera from north-western Australia (Köhler 2010a, 2010b, 2011a, 2011b, 2011c; Criscione et al. 2012; Köhler and Johnson 2012; Köhler and Shea 2012; Criscione and Köhler 2013, in press). Correspondingly, large numbers of new camaenids have recently been described from eastern Australia (Zhang and Shea 2008; Clark 2009; Stanisic 2009; Stanisic et al. 2010). As a result of these studies, the number of known camaenid species in Australia has more than doubled within the last three to four decades to approximately 800. However, apart from the north-western Australian Kimberley and the eastern continental fringes, many Australian regions have remained poorly surveyed. One of these areas is the so-called “Top End” of the Northern Territory. The camaenid fauna of this vast and remote landscape is mainly known from the faunal lists of Iredale (1933, 1938). Few recent taxonomic treatments are available and these deal only with a small number of species from restricted areas (Solem 1979; Willan et al. 2009; Köhler 2012). ∗ Corresponding
Similarly, the present work is based on the comparative study of a few museum samples that come from three isolated localities in Arnhem Land. The samples examined here stem from the collections of the Australian Museum, and have been recognised as representing a yet undescribed camaenid taxon. This study formally describes this new genus and species of Australian camaenid as part of ongoing revisionary work, which seeks to complete a comprehensive documentation of the camaenid fauna of the Northern Territory.
Materials and methods This study is based on ethanol preserved samples deposited in the Malacology Collection of the Australian Museum, Sydney (AM) and in the Museum and Art Galleries of the Northern Territory (NTM). Shell characters (dimensions, colouration, and sculpture) were assessed from all adult shells. Adults were recognised by a complete apertural lip. Shell height (H = maximum dimension parallel to axis of coiling, including lip) and shell diameter (D = maximum dimension perpendicular to H , including lip) were measured with callipers with a precision of 0.1 mm. The number of whorls (N ), including the protoconch, was counted with a precision of 0.1 as shown in Köhler (2011b; Figure 2). One representative specimen each from the type locality and the Gove Peninsula was dissected in order to study the genital anatomy by use of a Leica M8 stereo microscope with a drawing apparatus.
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© 2013 The Malacological Society of Australasia and the Society for the Study of Molluscan Diversity
New camaenid genus
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Abbreviations al — albumen gland; AM — Australian Museum, Sydney; at — atrium; bc — bursa copulatrix; D — shell diameter; elp — epiphallic longitudinal pilaster; vp — vergic epiphallic pore; ep — epiphallus; fl — flagellum; fo — free oviduct; H — shell height; hd — hermaphroditic duct; lp — longitudinal pilasters; W — number of shell whorls; NT — Northern Territory; NTM — Museum and Art Galleries of the Northern Territory, Darwin; p — penis; pf — penial folds; rm — retractor muscle; so — spermoviduct; tb — tubercles; vd — vas deferens; vg — vagina; wet — number of ethanol-preserved specimen(s). Systematics Gastropoda Heterobranchia Stylommatophora Camaenidae Pilsbry, 1895 Arnhemtrachia n. gen. Type species: Arnhemtrachia ramingining n. sp. Etymology Composed of “Arnhem” (for the region of Arnhem Land in the Northern Territory) and the Latin word “trachia” (= windpipe, from Greek “trachea”). The suffix “–trachia” has been employed for several Australian camaenids for the resemblance of radial ribs on shells with annular bands of cartilage that reinforce the windpipe of mammals; noun of feminine gender. Description Shell: Rather small (D < 13.5 mm), with strongly depressed spire and discoidal shape, keeled periphery, shallow suture. Umbilicus open, wide, weakly concealed by outer lip. Teleoconch sculpture comprising densely arranged, regularly spaced, well-developed radial ribs extending onto shell base and into umbilicus, periostracum smooth. Protoconch with fine microsculpture of dense, regular radial ribs. Aperture simple, rounded, without nodes; outer lip thin, expanded. Colour light brown with slightly darker, brown peripheral band. Reproductive tract: Typically, camaenid with prostate and uterus being fused forming spermoviduct, bursa copulatrix lacking diverticulum and genitalia lacking stimulatory organs. Vas deferens terminating in epiphallus near the flagellum of the latter. Epiphallus well developed, connecting to penis though a narrow duct; communicates to penial interior through simple vergic opening lined by thick-walled sub-circular ridge with epiphallic flagellum, about as long as epiphallus. Penis without penial sheath. Penis elongated, not coiled, inner penial
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wall with well developed, slightly undulating longitudinal pilasters. Penial retractor muscle extremely short, originating from diaphragm, inserting on distal third of epiphallus. Bursa copulatrix elongated, reaching proximal base of spermoviduct. Remarks Arnhemtrachia differs from other camaenids by a combination of distinct shell and genital characters to an extent that justifies the recognition of a new genus. Genera from north-western Australia with a similarly small, flat shell with radial ribs are Baudinella Thiele, 1931, Setobaudinia Iredale, 1933, Torresitrachia Iredale, 1939, and some species of Ordtrachia Solem, 1984, Mouldingia Solem, 1984, and Carinotrachia Solem, 1985. Shells of Torresitrachia, Baudinella, and Setobaudinia differ most conspicuously by absence of a peripheral keel. In addition, all these taxa have a distinct genital anatomy (Solem 1985; Köhler 2011b). Ordtrachia differs by absence of radial ribs on the shell and distinct microsculpture, as well as by very different genital anatomy (Solem 1984). Mouldingia differs by distinct shell shape, strikingly different sculpture, microsculpture and genital anatomy (Solem 1984). The most similar Australian camaenid is Trozena morata Iredale, 1938, a species from NE Queensland. The monotypic genus Trozena Iredale, 1938 differs in the following characters: shell keel super-peripheral, protoconch with microsculpture of bold pustules and coarse radial ridges, teleoconch with weaker radial ribs and microsculpture of wavy periostracal ridges (Stanisic et al. 2010). Its genital anatomy reveals several similarities (e.g. very long epiphallus, stubby retractor muscle attaching midepiphallus, elongate bursa copulatrix) but differs in its elongate atrium, vastly different penial wall sculpture, presence of a penial caecum and short flagellum (Solem 1979: 116–119). Arnhemtrachia ramingining n. sp. (Figures 1–3). Holotype Australia, Northern Territory, West Arnhem Land, south of Ramingining, 27.8 km south of Arafura Homestead, 12◦ 41.13 S, 134◦ 49.25 E, in vine thicket near edge of plateau, rocky ground, under rocks; coll. Vince Kessner, 2 July 2007 (NTM P 48938, dissected specimen). Paratypes Same data as holotype, 2 wet (AM C.462972); 34.8 km S of Old Arafura homestead, turn-off 56.8 km S of Ramingining, 12◦ 41.65 S, 134◦ 49.23 E, sealed to rocks and leaves in vine thicket; coll. Vince Kessner, 22 August 1986, 13 dry (AM C.152285); 6.8 km S of Old Arafura homestead, turnoff 28.8 km S of Ramingining,
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Figure 1. Shell photographs (top, front and bottom view): A, paratype AM C.462972; B, East Arnhem Land, Nhulunbuy AM C.462975; C, East Arnhem Land, Yirrkala AM C.467038. Scale bar = 10 mm.
12◦ 29.68 S, 134◦ 53 E, sealed to rocks and leaves in vine thicket; coll. Vince Kessner, 22 August 1986, 41 dry (AM C.152286, 41 dry).
Etymology For Ramingining, closest settlement to type locality; noun in the nominal case.
Additional, non-type material East Arnhem Land, Gove Peninsula, Nhulunbuy near ALCO plant, 12◦ 11.38 S, 136◦ 41.94 E in vine thicket behind beach, under logs, sealed to fallen leaves; coll. Vince Kessner, 4 July 2007), 1 wet (AM C.462975), Yirrkala, coll. J. Gillett, 14 January 1982, 4 wet (AM C.467037), near plantation, on shrubs; coll. J. Gillett, 7 April 1982), 12 wet (AM C.467038), behind banana plantation, in scrub on trees; coll. P.H. Colman, 25 March 1980, 22 wet (AM C.467039).
Description Shell (Figures 1–2): Small (Table 1), strongly depressed spire, discoidal shape, keeled periphery, shallow suture, colour light brown with inconspicuous peripheral band. Umbilicus open, wide, occupying about one fourth of base. Teleoconch with dense, regularly spaced, radial ribs extending onto shell base and into umbilicus, periostracum smooth. Protoconch with microsculpture of dense, regular radial ridgelets. Aperture simple, rounded, without nodes; outer lip thin, expanded.
Figure 2. Scanning electron micrographs of shell sculpture, holotype NTM P 48938 (shell crushed for dissection). A, protoconch viewed from above; B, sculpture on last whorl viewed from above. Scale bars = 1 mm.
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Table 1. Comparison of shell dimensions of the type series of A. ramingining n. sp. and specimens from the Gove Peninsula (A. cf. ramingining). Given are minimum – maximum (average ± standard deviation) for N measured specimens, in mm. Sample
N
H
D
W
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Holotype 1 5.5 13.5 4 NTM P 48938 Paratypes 16 4.8–5.6 9.7–13.5 3.7–4.1 AM C. 152285-6 (5.2 ± 0.2) (11.2 ± 0.9) (4.0 ± 0.1) Gove Peninsula 22 4.7–5.7 9.7–12.2 3.8–4.1 populations AM C.467037-9 (5.0 ± 0.2) (10.7 ± 0.5) (4.0 ± 0.1)
Figure 4. Known occurrences of A. ramingining in Arnhem Land, Northern Territory: *—type locality in West Arnhem Land, south of Ramingining, •—additional localities in West Arnhem Land (near Old Arafura Homestead) and East Arnhem Land (Yirrkala and Nhulunbuy).
Figure 3. Genital anatomy, holotype NTM P 48938: A, genital system; B, penial anatomy.
Reproductive tract (Figure 3): Epiphallus very long, coiled, about twice as long as penis, with very long flagellum; stubby retractor muscle attaching at mid-epiphallus; inner epiphallic wall with two longitudinal pilasters; epiphallus opening into penial lumen through vergic pore. Inner penial wall with well-developed longitudinal pilasters extending entire length; at distal third of wall one broad lateral pilaster running transverse to all other pilasters, tapering towards distal end of penial wall; epiphallus opening through complexly folded extensions of epiphallic pilasters, which extend into penis. Vagina as long as penis, inner vaginal wall with well-developed transverse-longitudinal pilasters extending into bursa copulatrix and free oviduct; free oviduct twice as long as vagina, bursa copulatrix elongate, simple.
Remarks Arnhemtrachia ramingining is known from a few museum samples from localities that are a considerable distance from each other. The type locality is more than 50 km south of Ramingining. In addition, the species is reported from near the Old Arafura Homestead, about 60 km west of the type locality, and from the Gove Peninsula, about 200 km east from the type locality (Figure 4). These three geographically isolated populations reveal consistent shell features (sculpture and shell size; Table 1). Dissections of a single specimen from the type locality and one from Yirrkala, Gove Peninsula, revealed similar penial morphology. Thus, based on morphological grounds, we consider all populations to be conspecific. The scattered distribution of records is presumably an artefact of poor sampling and is probably not indicative of a fragmented distribution of this species. Unfortunately, we were unable to infer the amount of genetic differentiation through DNA extraction due to the age and state of preservation of the samples. Arnhemtrachia ramingining aestivates during the dry season sealed to substrates in sheltered places. It appears to pursue an arboreal or semi-arboreal life style when active during the wet season as it was found on trees. Discussion The camaenid fauna of Arnhem Land has never been surveyed to an extent comparable with other parts of the country, such as the Kimberley, the MacDonnell Ranges
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in Central Australia or the mesic zone in eastern Australia. Most species are known from sporadic reports based on material that has accumulated in museums from opportunistic collections made over many years. This neglect is unfortunate because, based on the scant available data, Arnhem Land appears to harbour a distinct camaenid fauna compared with its neighbouring regions. Camaenid groups known from this region are usually endemic, morphologically distinct, phylogenetically enigmatic and often taxonomically impoverished. Typical examples are the two monotypic genera Arnemelassa Iredale, 1938 (from East Arnhem Land) and Parglogenia Iredale, 1938 (from West Arnhem Land), which are characterised by genital anatomies that differ markedly from any other Australian camaenid genus while their phylogenetic relationships remain uncertain (Köhler 2012). Correspondingly, a combination of distinct features of the shell morphology and genital anatomy highlight the taxonomic distinctiveness of Arnhemtrachia n. gen. from any other camaenid genus known from Arnhem Land and surrounds. Surprisingly, the closest camaenid in terms of morphological similarity appears to be a species from NE Queensland, Trozena morata. Biogeographic scenarios suggest that ancestors of modern Australian camaenids arrived in Australia from Papua New Guinea (Hugall and Stanisic 2011). If that is correct, the enigmatic and distinct camaenids of Arnhem Land might be amongst the oldest groups in Australia, holding the key to resolving the phylogenetic relationships between modern-day eastern and western Australian camaenid groups. The present work suggests that more comprehensive surveys are urgently needed to better document land snail diversity in the region. In comparison to the restricted distributions of most other camaenids in north-western Australia, the ranges of all three known Arnhem Land endemics Arnemelassa creedi (Cox, 1868), Parglogenia pelodes (Pfeiffer, 1846), and A. ramingining, are comparatively large, with maximum linear distances between 100 and 200 km (Köhler 2012). However, the narrowly endemic distributions of camaenids, particularly in the Western Australian Kimberley, have been attributed to the restricted and fragmented distribution of their habitats, such as vine thickets and rainforest patches (Gibson and Köhler 2012). By contrast, camaenids inhabiting more open landscapes were shown to have larger ranges than these rainforest species. Species of Exiligada Iredale, 1939 from the Victoria River District, NT may serve as an example. These inhabit rocky outcrops in the semi-arid savannah bush land of the Wet Tropics, and species ranges were found to reach 200 km of linear distance (Criscione et al. 2012). Correspondingly, the wider distributions of camaenids in Arnhem Land might be due to the large expanse of suitable habitat in Arnhem Land—rocky outcrops and dry vine thickets.
Acknowledgements This work has been made possible through financial support from the Australian Government (ABRS grants RF210-05 to FK). Special thanks are due to Morgan Laudine (Newcastle) for producing illustrations of genitalia, and to Sue Lindsay (AM) for conducting the SEM work. Two reviewers, Gary Barker and John Stanisic, and Winston Ponder, provided helpful comments on the manuscript of this paper, which are most gratefully acknowledged.
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