Research Article |
Corresponding author: Frank Köhler ( frank.koehler@austmus.gov.au ) Academic editor: Thomas von Rintelen
© 2022 Frank Köhler, Michael Shea.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Köhler F, Shea M (2022) A new cryptic species of land snail from the Northern Territory, Australia (Stylommatophora, Camaenidae, Parglogenia). Zoosystematics and Evolution 98(2): 427-433. https://doi.org/10.3897/zse.98.93851
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Parglogenia cobourgensis sp. nov., a new species of camaenid land snail is described from Cobourg Peninsula, Top End of the Northern Territory in Australia. This new species has a shell that is identical to the type species of the genus, Parglogenia pelodes, which also occurs in the Top End. However, both species clearly differ in their reproductive anatomy and are also well-differentiated in terms of mitochondrial phylogenetics. A single specimen of a Parglogenia species from Croker Island, West Arnhem Land, is hypothesized to represent a third species based on details of its reproductive anatomy. However, only a single historical specimen was available for study. We therefore refrain from formally naming this species because of the incomplete information at hand. Helix subgranosa Le Guillou, 1842, a nominal species previously placed in Parglogenia, is synonymized with Xanthomelon durvillii (Hombron & Jacquinot, 1841).
Eupulmonata, Helicoidea, land snail, Stylommatophora, taxonomy
The camaenid Parglogenia Iredale, 1938 is a monotypic genus endemic to the Top End of the Northern Territory in the Australian Monsoon Tropics. Its only known member is Parglogenia pelodes (Pfeiffer, 1846), which is known to occur in the western part of the Top End, including the surroundings of Darwin, West Arnhem Land, the Cobourg Peninsula, and the Tiwi Islands. Another camaenid that exhibits a rather similar shell in terms of overall size and shape is Arnemelassa creedi (Cox, 1868). Arnemelassa creedi replaces Parglogenia in the eastern part of the Top End and the species are not known to occur in sympatry. Despite their conchological similarity, both Parglogenia and Arnemelassa exhibit vastly different reproductive anatomies indicating that despite their similar shell these species are not closely related (
Historically, the identity and delimitation of Parglogenia pelodes has been somewhat controversial mainly because of the imprecise type locality and the fact that no type material was known to exist. To remove nomenclatural uncertainty,
Subsequently, mitochondrial DNA sequences of Parglogenia and Arnemelassa have been included in a phylogenetic study of the Camaenidae from north-western Australia. This study confirmed that the taxa are indeed not immediately related although belonging to the same principal clade (
Our report of a new, morphologically cryptic species in Parglogenia adds to earlier discoveries of cryptic camaenid land snail species in the Northern Territory. Notably, we showed earlier that the Top End harbours three cryptic species of Xanthomelon that cannot be distinguished from each other by their shell (
This study is based on analyses of ethanol preserved specimens and dry shell material, including types, deposited in the collections of the
Australian Museum (
Dimensions of fully mature shells (as recognised by a finished apertural lip) were measured with callipers precise to 0.1 mm: Height of shell (H), diameter of shell (D). Whorls were counted as described by
Genomic DNA was extracted from small pieces of foot muscle using a QIAGEN DNA extraction kit for animal tissue following the standard procedure of the manual. Fragments of two mitochondrial genes, 16S rRNA (16S) and cytochrome c oxidase subunit 1 (COI), were amplified by PCR using the primer pairs 16Scs1 (5′-AAACATACCTTTTGCATAATGG-3′) (
Our sequence data set contained concatenated sequences of COI and 16S from 17 camaenids, of which nine sequences were of Parglogenia. The 16S alignment consisted of 732 base pairs and the COI of 655 base pairs. We selected several species that are more closely related to Parglogenia as outgroup representatives based on phylogenetic tree of north-western Australian Camaenidae presented by
Sequences used for phylogenetic reconstruction with GenBank and museum registration numbers.
Species | Location | Museum Voucher | GenBank: 16S | GenBank: COI |
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Arnemelassa creedi | Australia, West Arnhem Land |
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HQ245442 | KP085373 |
Arnemelassa creedi | Australia, West Arnhem Land |
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ON532885 | ON534065 |
Chloritis eustoma | Solomon Islands, Malaita |
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ON532893 | ON534074 |
Parachloritis argilacea | Timor-Leste |
|
HG515231 | HG515082 |
Parachloritis argilacea | Timor-Leste |
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HG515229 | HG515084 |
Parglogenia cobourgensis | Australia, Cobourg Peninsula |
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KP085079 | KP085395 |
Parglogenia cobourgensis | Australia, Cobourg Peninsula |
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HQ245508 | ON534066 |
Parglogenia cobourgensis | Australia, Cobourg Peninsula |
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ON532886 | ON534067 |
Parglogenia pelodes | Australia, Darwin, Buffalo Creek | NTM P63374 | ON532887 | ON534068 |
Parglogenia pelodes | Australia, Darwin, Buffalo Creek | NTM P63374 | ON532888 | ON534069 |
Parglogenia pelodes | Australia, Darwin, East Point Reserve | NTM P63373 | ON532889 | ON534070 |
Parglogenia pelodes | Australia, Darwin, East Point Reserve | NTM P63373 | ON532890 | ON534071 |
Parglogenia pelodes | Australia, Darwin, Buffalo Creek |
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ON532891 | ON534072 |
Parglogenia pelodes | Australia, Darwin, Buffalo Creek |
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ON532892 | ON534073 |
Torresitrachia bathurstensis | Australia, Kimberley | WAM S49549 | KP085090 | KP085409 |
Torresitrachia eclipsis | Australia, Kimberley | WAM S49356 | KP085093 | KP085412 |
Youwanjela wilsoni | Australia, Kimberley | WAM S49583 | HE588141 | KP085427 |
The phylogenetic tree (Fig.
Maximum Likelihood bootstrap consensus tree for a concatenated alignment of mitochondrial 16S and COI sequences for selected Camaenidae from Northern Australia, Timor-Leste, and the Solomon Islands. Numbers next to branches indicate nodal support by means of ultrafast bootstrapping. Scale bar: 30% modelled sequence divergence.
Among the included species, Parachloritis argilacea from Timor-Leste is the sister taxon of Parglogenia. Youwanjela wilsoni from the Kimberley and Chloritis eustoma from Malaita, Solomon Islands are also more closely related.
Uncorrected genetic p-distances in COI were 0.14%–0.4% (on average 0.3%) among sequences of Parglogenia cobourgensis (n = 3) and between 0 and 1.8% (on average 0.9%) among sequences of Parglogenia pelodes (n = 6). Interspecific genetic distances between both species ranged from 13.2% to 13.9% (on average 13.4%).
Helix pelodes Pfeiffer, 1846, by original designation.
Helix pelodes
Pfeiffer, 1846: 126 (‘north coast of Australia’). Neotype FMNH 182450, Darwin, Dudley Point (12°24'S, 130°49'E), designated by
Helix prunum
– Pfeiffer 1851 [in 1849–1853]: 54, pl. 74, figs 11–13; Reeve 1852 [in 1851–1854]: pl. 68, fig. 353;
Chloritis pseudoprunum Pilsbry, 1893: 271 (‘Port Darwin’; Holotype ANSP 62411).
Parglogenia pelodes
–
Since its original description, the name Helix pelodes has been shrouded in uncertainty until relatively recently. Pfeiffer (1851 [in 1849–1853]), subsequently treated H. pelodes as a junior synonym of Helix prunum Férussac, 1821. Subsequently,
Shell relatively large (D = 14.3–31.5 mm, H = 10.8–20.3 mm; n = 92), with strongly and almost evenly elevated spire, comprising between 4.5 and 5.8 whorls. Apical sculpture of anastomosing ridges initially, becoming pustulated after first half whorl. Postapical whorls with microsculpture of very small, rather widely spaced setae and extremely fine ridgelets with weak radial ribs appearing on spire and body whorl. Umbilicus very narrow, partly covered by reflected lip, internally with crowded pustules. Body whorl globose, rounded, only slightly descending behind strongly reflected, thin, white lip. Shell light yellow brown, uniform. Vagina and penis very long, atrium short, bursa copulatrix very short, without enlarged head. Free oviduct with glandular, convoluted walls. Vas deferens with bifurcated caecum on ascending arm and entering the epiphallus near insertion of penial retractor muscle without differentiation. A narrow, raised ridge separates the epiphallus from the penis; inner penial walls with longitudinal corrugated ridges; no penial sheath, verge, or epiphallic appendages present (
AUSTRALIA · 1 preserved specimen; Northern Territory, Cobourg Peninsula, 3.4 km NE of Black Point Ranger Station; 11°08'27.6"S, 132°10'12.0"E; vine thicket; leg. Vince Kessner, 4 Feb 2007;
AUSTRALIA · 1 preserved specimen; same data as holotype;
Australia, Northern Territory, Cobourg Peninsula, 3.4 km NE of Black Point Ranger Station (11°08'27.6"S, 132°10'12.0"E).
For Cobourg Peninsula, where this species occurs.
AUSTRALIA · 1 dry shell; Northern Territory, Port Essington; 11°16'S, 132°9'E; leg. 1900;
Shell (Fig.
Reproductive anatomy (Fig.
Anatomy of Parglogenia species. A–D. Parglogenia cobourgensis holotype
Head wart oval to trunk-shaped, about 2×3 to 3×5 mm in size (Fig.
Shell effectively indistinguishable from Parglogenia pelodes. Fewer shells of P. cobourgensis were available for examination. These completely overlapped in size range with P. pelodes occupying a smaller size range overall. This species differs from P. pelodes most conspicuously in having a completely different penial wall sculpture (P. pelodes has longitudinal corrugated ridges) and by having much shorter penis, epiphallus, vagina, and bursa copulatrix.
The distribution of Parglogenia cobourgensis is difficult to delineate due to the paucity of suitable material. Here, the known distribution of P. cobourgensis is restricted to the Cobourg Peninsula and coastal parts of west Arnhem Land excluding Croker Island (see below). Denser sampling is required to delimitate the distributions of P. pelodes and P. cobourgensis more accurately and to clarify the taxonomic status of the Croker Island population.
AUSTRALIA · 1 preserved specimen, 4 dried shells; Northern Territory, Croker Island, near airstrip; 11°10'0"S, 132°29'6"E; leg. 28 Mar 1980;
Shell (Fig.
Reproductive anatomy (Fig.
Shell effectively indistinguishable from P. pelodes and P. cobourgensis. The few available specimens are at the larger end of the size distribution in this genus, but this might be a sampling artifact. Differs from P. pelodes most conspicuously in having a completely different penial wall sculpture that resembles P. cobourgensis. From P. cobourgensis, the Croker Island specimen differs in having a shorter bursa copulatrix, a broad spermathecal head, and a slightly longer epiphallus (one fifth of penis vs. one sixth to one tenth of penis length), inner penial wall has several longitudinal pilasters instead of only two.
Just a single historical specimen was available for dissection and not suitable for DNA extraction. For the paucity of suitable material, we refrain from a formal description of the Croker Island species.
Presumably endemic to Croker Island.
Thanks are due to Vince Kessner for collecting much of the material used in the present study. We thank Isabel Hyman and Junn Foon for carefully reviewing an earlier version of this manuscript. Their comments have helped to improve the quality of this work.