Ennea nigeriensis, de Winter & de Gier, 2019

de Winter, A. J. & de Gier, Werner, 2019, A new Nigerian hunter snail species related to Enneaserrata d'Ailly, 1896 (Gastropoda, Pulmonata, Streptaxidae) with notes on the West African species attributed to Parennea Pilsbry, 1919, ZooKeys 840, pp. 21-34 : 25-30

Ennea nigeriensis sp. n. Figs 1 G–K, 2 F–M, 3 F–J

Material examined.

Holotype ( RMNH.MOL.341194) NIGERIA, Cross River State, Agbokim ; 5.9833N, 8.7500E, alt. <100 m; O.C. Oke leg. Other material: 4 voucher shells ( RMNH.MOL.341195), same data as holotype.

Diagnosis.

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.

Description.

Shell dimensions: see Table 1. Shell elongate cylindrical or elongate-ovoid, greatest width at penultimate whorl, last whorls less convex than upper whorls, apex subconical. Shell height 5.1 - 6.6 mm with c. 6½ - 7½ whorls. Protoconch large, c. 2¾ whorls, smoothish, protoconch suture simple, transition to teleoconch marked by the onset of the crenulated teleoconch suture. Teleoconch behind the aperture for a short distance with very fine, sharp, distant ribs, rest of the shell with irregular growth lines, the subsutural crenulations at some spots extending into indistinct, low ribs. Suture deep. Umbilicus closed, umbilical region behind the basal lip with fine, sharp ribs. Peristome entire, palatal, basal and columellar wall wide but not strongly reflected, parietal wall with a deep indentation above the strong, protruding angularis. Palatal wall with a blunt mid-palatal swelling. Columellar plate externally appearing as a widened plate with a median protrusion. CT scanning shows the columella as a slightly twisted pilaster with a single small dilatation (Fig. 3C, E). Angular lamella coils regularly inwards for about half a whorl, gradually diminishing in height (Fig. 3C, D). Even more strongly than in E. serrata , an ad-apertural view suggests the angular lamella to have an initial hairpin turn which in fact is caused by the lamella being continuous with the angular tooth. A single palatal fold, corresponding with a single, not very deep, external depression, runs for almost an entire whorl from its starting point on the inner wall above the angular tooth towards the palatal peristome lip; its termination is obscured by a swelling of the palatal lip. In transparent shells the internal lamella can be externally seen starting above the peristome as far as the point which the parietal and palatal walls join. This was confirmed by CT scans of the holotype shell, which also demonstrate the absence of a second palatal fold (Fig. 3 A–C).

Ecology.

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.

Remarks.

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. Pilsbry’s (1919) characters defining Ennea and Parennea do not appear to delimit natural groups of species. Both taxa exhibit the same variation in shell shape, the shells are either cylindrical or elongate ovoid (cf. Figs 1A, 2A, Figs 1G, 2F). Ennea nigeriensis is rather variable in shell height, but on average considerably shorter (Table 1). One exceptionally tall specimen is only a trifle shorter than the shells of E. serrata , but is substantially (20%) less wide (Fig. 2 K–M; Table 1). In the two known shells of E. serrata , the upper half of the palatal lip is more strongly receding than in nigeriensis shells. The distance between the known localities of the two taxa is c. 200 km. Further collecting, especially of live snails, is required to test the taxonomic decisions taken.

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 ( Adam and Van Goethem 1978).

The identity of Ptychotrema (Parennea) sulciferum sensu Degner in Liberia

Degner recorded Ptychotrema (Parennea) sulciferum (Morelet, 1884) from Du River, Liberia and provided line drawings of three shells ( Degner 1934b, fig. 8). This species was described from Landana, Cabinda (exclave of Angola), and later recorded from Angola, Uganda ( van Bruggen 1989) and Cameroon ( de Winter 2008). The Liberian record was not addressed in two major Parennea studies ( Adam and Van Goethem 1978; van Bruggen 1989). De Winter (2008) refuted Degner’s specific identification and suggested the Liberian shells to belong to an as yet unknown Parennea species. In Degner’s drawings the characteristic acuminate apex of P. sulcifera is lacking, but they do show a single palatal fold on the last whorl characteristic for Parennea species. Degner’s material was collected by Joseph Bequaert and could be borrowed from his collection in MCZ. Study of the three specimens revealed the presence of a second palatal fold and a shallow and easily overlooked additional furrow on the back of the shell (Fig. 4D, E). These characters assign the species to Ennea rather than Parennea .

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 ( Degner 1934a) as Pt. (E.) elegantulum (L Pfeiffer, 1846). However, in the very same paper in which P. sulcifera was reported, Degner (1934b: 372, footnote) corrected his previous identification of Pt. (E.) elegantulum to Pt. (E.) thompsonae Connolly, 1928. Curiously, in the same paper in which Degner (1934b) reported P. sulcifera from Du River, he also recorded E. thompsonae from that locality. Obviously an error occurred. It seems likely that all shells from Du River belong to the same species. We assume that Degner misidentified the three shells as Parennea due to their unusual small size and rather eroded state, largely (but not completely) obscuring the characteristic (for E. thompsonae ) crenulated suture. We provisionally identify this species as Ennea cf. thompsonae , as the shells from Du River are noticeably smaller than the type material of this species from Sierra Leone (see Connolly 1928).

Although Degner (1934b) acknowledged that his previously published description and figure of the genital anatomy of Pt. (E.) elegantulum actually related to E. thompsonae , some subsequent authors were apparently unaware of Degner’s correction (but not Adam et al. 1994). For instance, Schileyko (2000: 798, fig. 1040) based his anatomical characterization of Ennea on Degner’s (1934a) illustration of E. elegantula , thus on E. thompsonae (but provided a drawing of a correctly identified shell). Also Binder (1963) illustrated the genital anatomy of E. elegantula with Degner’s drawings, but provided shell drawings of what appears to be true E. elegantula (as did Daget 2003, who copied Binder’s figures). Remarkably little is known of the type species of Ennea , including its anatomy and distribution.

The identity of Ptychotrema (Parennea) aequatoriale sensu van Bruggen in Nigeria

Van Bruggen (1991) identified a single damaged shell from Kwale, Nigeria, as Pt. (Parennea) aequatoriale Pilsbry, 1919, a species originally described from the Ituri forest in the eastern DR Congo. This species was subsequently recorded from various other Nigerian localities (e.g., Oke and Alohan 2006; Oke and Chokor 2009). Comparison of the Nigerian specimen studied by van Bruggen (RMNH.MOL.273794, Fig. 5 A–D) with drawings of the holotype shell of P. aequatorialis ( Pilsbry 1919, fig. 83) and shell drawings in Adam and Van Goethem (1978, figs 20, 21) shows significant differences. We illustrate a specimen P. aequatorialis from Yanongo, eastern DR Congo (Fig. 5 E–H). The Nigerian shell is similar in size (4.1 × 2.2 mm), but differs in its more elongate shape, much less acuminate apex, wider umbilicus, and less distant ribbing on the teleoconch without spiral sculpture in the interstices. However, the most significant difference is the presence of a second palatal fold and correspond ing second external furrow, indicating that this species cannot be a Parennea , but by definition, is a species of Ennea . The Nigerian specimen resembles the original illustration of Ennea perforata d’Ailly, 1896, a not uncommon, but surprisingly little known species that was described on the basis of a single shell from an unknown locality in Cameroon. This species has been reported from various localities in Cameroon ( Jaeckel 1956; de Winter and Gittenberger 1998) as well as from Bioko ( Germain 1916; Ortiz de Zarate Lopez and Ortiz de Zarate Rocandio 1956; Wronski et al. 2014). We tentatively identify the Nigerian specimen as Ennea cf. perforata in view of the variability of the Nigerian and Cameroonian material (unpublished data), and the unclear status of some similar nominal species. A revision of this species group is in preparation.