Research Article |
Corresponding author: A.J. de Winter ( ton.dewinter@naturalis.nl ) Academic editor: Menno Schilthuizen
© 2019 A.J. de Winter, Werner de Gier.
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:
de Winter AJ, de Gier W (2019) A new Nigerian hunter snail species related to Ennea serrata d’Ailly, 1896 (Gastropoda, Pulmonata, Streptaxidae) with notes on the West African species attributed to Parennea Pilsbry, 1919. ZooKeys 840: 21-34. https://doi.org/10.3897/zookeys.840.33878
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Ennea nigeriensis sp. n. is described from southeastern Nigeria on the basis of external and internal shell morphology. Following Pilsbry’s formal criteria of a single palatal fold and corresponding external furrow, the new species may be assigned to Parennea. Ennea nigeriensis sp. n. exhibits substantial similarity with E. serrata, a species from Cameroon, in the cylindrical shell shape, crenulate suture, and internal shell morphology, indicating that the two species are closely related. CT scanning confirmed the presence of only a single palatal fold in E. nigeriensis sp. n. and two in E. serrata. In spite of this, the Nigerian species is provisionally assigned to Ennea rather than Parennea, suggesting that the characters used to define Ennea and Parennea are insufficient to delimit natural groups of species. The holotype of E. serrata is examined for the first time since its description in 1896 and a redescription of the species is provided based on the two shells hitherto known.
Study of the original specimens recorded as Ptychotrema (Parennea) sulciferum by Degner from Liberia reveals these to belong to Ennea cf. thompsonae. The Nigerian shell recorded by van Bruggen as Ptychotrema (Parennea) aequatoriale proved to be a specimen of Ennea cf. perforata. As a result, no species attributable to Parennea now appear to be known in West Africa; in contrast, numerous species are known from central and eastern Africa.
Afrotropical region, Cameroon, computerised tomography, land snail, Liberia, Nigeria, Ptychotrema, shell morphology, Stylommatophora, taxonomy
The land snail fauna of the Southwest Province of Cameroon (effectively, the area around Mount Cameroon) is comparatively well known due to the pioneering work by
Still, our knowledge is far from complete. Various species are only known by the original description and often have inaccurate locality data. One example is the streptaxid Ennea serrata d’Ailly, 1896, which was described from “Camerunia”. Adolf
This investigation was triggered by the discovery of a Nigerian streptaxid species that we initially attributed to Parennea, because only a single palatal fold and corresponding external furrow were seen in the shell aperture. In shape and sculpture it strongly resembles the original illustrations of E. serrata. However, according to the description by
Parennea species have been reported from throughout Equatorial Africa. The Democratic Republic of the Congo (formerly Belgian Congo and Zaire) has by far the largest diversity, but the taxon has also been reported from Angola, Cameroon, Ethiopia, Gabon, Kenya, Malawi, Rwanda, Somalia, Tanzania, and Uganda (
The classification of African Streptaxidae is presently still largely based on
This paper is dedicated to the memory of Professor Chris Omamoke Oke, who passed away in September 2018. Chris was one of precious few terrestrial malacologists in West Africa, working at Benin University, Nigeria, for more than 25 years. His untimely death is a great loss for the field of African non-marine Malacology. We lost a dear colleague, who contributed greatly to this paper.
The following acronyms have been used for museum collections:
Shells were measured and photographed using a Leica M165c stereo microscope with a Leica DFC420 microscope-mounted camera using Leica LAS 4.4 software and Helicon Focus stacking software. The holotype of E. serrata (in alcohol) and the holotype of the new taxon from Nigeria were scanned with a Bruker SkyScan1172 Micro-CT scanner (Naturalis Biodiversity Center, Leiden). A voltage of 40 kV was used with a flux of 250 µA, at a full 360° rotation. Medium camera settings were used, with a runtime of approximately 30 minutes. The dry shell of the new taxon from Nigeria was mounted in a gelatin capsule filled with cotton wool, while the holotype of E. serrata was mounted in a plastic tube filled with ethanol. Projection images were trimmed and reconstructed using Bruker’s NRecon software. The reconstructed TIFF-images were fully rendered in Avizo 9.4.0 (
Ennea serrata d’Ailly, 1896: 17, pl. 1, figs 38–41.
Ptychotrema (Ennea) serrata
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Ptychotrema (Ennea) serratum
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Holotype (
The specimen reported by
Mean shell height 7.1 mm, with c. 7 whorls, mean shell diameter 2.85 mm (Table
Shell measurements of Ennea serrata d’Ailly and E. nigeriensis sp. n. Abbreviations: SH, shell height; SD, shell diameter; HLW, height of last whorl; PH, peristome height; PD, peristome diameter; W, number of whorls; CT, coiling tightness W:lnH.
SH | SD | HLW | PH | PW | W | SH/SD | HLW/SH | PH/HLW | PH/SH | PH/PW | CT | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Ennea nigeriensis | Holotype | 5.1 | 2.2 | 2.4 | 1.6 | 1.4 | 6.5 | 2.4 | 0.5 | 0.7 | 0.3 | 1.1 | 4.0 |
voucher 1 | 5.3 | 2.2 | 2.5 | 1.6 | 1.5 | 6.5 | 2.4 | 0.5 | 0.6 | 0.3 | 1.1 | 3.9 | |
voucher 2 | 6.6 | 2.4 | 2.9 | 1.9 | 1.7 | 7.6 | 2.7 | 0.4 | 0.6 | 0.3 | 1.1 | 4.0 | |
voucher 3 | 5.7 | 2.4 | 2.7 | 1.8 | 1.6 | 6.9 | 2.4 | 0.5 | 0.6 | 0.3 | 1.1 | 4.0 | |
voucher 4 | 5.3 | 2.1 | 2.4 | 1.6 | 1.5 | 6.5 | 2.5 | 0.5 | 0.7 | 0.3 | 1.1 | 3.9 | |
mean/median | 5.6 | 2.3 | 2.6 | 1.7 | 1.5 | 6.8 | 2.5 | 0.5 | 0.7 | 0.3 | 1.1 | 4.0 | |
Ennea serrata | holotype | 7.3 | 2.8 | 3.4 | 2.3 | 1.9 | 7.2 | 2.6 | 0.5 | 0.7 | 0.3 | 1.2 | 3.6 |
voucher |
6.9 | 2.9 | 3.3 | 2.1 | 2.0 | 6.9 | 2.3 | 0.5 | 0.6 | 0.3 | 1.1 | 3.6 |
The Musake specimen was found at 1850 m altitude in the litter layer of a rather moist montane forest rich in ferns, mosses and lichens (
Holotype (
Shell small, elongate-cylindrical to elongate ovoid (see also http://www.morphosource.org/Detail/SpecimenDetail/Show/specimen_id/21852). Shell surface with irregular growth lines and coarse subsutural crenulations extending into weak ribs further down the whorl. Shell strongly resembling that of E. serrata in shape and sculpture, but differing by the presence of a single palatal fold and corresponding external depression rather than two; in being ca. 20% less wide (and mostly much shorter), with ca. 10% less wide protoconch; and in having tighter coiled whorls.
Shell dimensions: see Table
The area where the species was collected lies at a rather low elevation, less than 100 m. It may have been collected near the Agbokim waterfall.
Although the apertural morphology of the Nigerian shells suggests these to be a member of Parennea, they strongly resemble the two known shells of E. serrata in overall morphology and are obviously closely related.
Ennea nigeriensis superficially resembles E. okei (de Winter, 1996), which is a much larger species with a short angular lamella, as well as a quite different internal shell morphology (unpublished CT data).
Ennea nigeriensis may be attributed to Parennea, but differs substantially from other species attributed to this taxon. The species is larger than most Parennea species known to date. Only P. circumcisa (Morelet, 1885), P. usambarensis (Verdcourt, 1958), P. sperabilis (Preston, 1910), and P. connollyi (Dupuis & Putzeys, 1922) possess shells larger than 5 mm. Judging from the available illustrations and descriptions, P. usambarensis from eastern Tanzania is somewhat similar in shape, size and in peristome morphology; its shell has strong ribs that extend over the entire whorl and is more tightly coiled, its palatal tooth seems sharper (resulting in a more sharply protruding lip in lateral view), and the palatal lamella seems to extend less far into the body whorl (
Computerised tomographic images of holotype shells of Ennea serrata d’Ailly, 1896 (A–E
Degner recorded Ptychotrema (Parennea) sulciferum (Morelet, 1884) from Du River, Liberia and provided line drawings of three shells (
An attempt to identify Degner’s specimens with a known Ennea species revealed a strong resemblance to shell drawings that Degner provided in another publication (
Although
A–C Shells of Ennea cf. thompsonae Connolly from Du River, Liberia (
We are indebted to Adam Baldinger (Museum of Comparative Zoology, Cambridge), Mattias Forshage (