Ennea serrata d'Ailly , 1896

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 : 23-24

Ennea serrata d'Ailly, 1896 Figs 1 A–F, 2 A–E, 3 A–E

Ennea serrata d’Ailly, 1896: 17, pl. 1, figs 38-41.

Ptychotrema (Ennea) serrata - Jaeckel 1956: 355.

Ptychotrema (Ennea) serratum - Adam et al. 1994: 89.

Material examined.

Holotype ( SMNH type-956 , in ethanol): CAMEROON " Camerunia, ubi?". Other material: CAMEROON, Kamerunberg , Musake Haus , 1850 m ( ZMB 101777 / 1 dry shell).

The specimen reported by Jaeckel (1956) proved to belong to this species and is the second specimen known. Study of both specimens, together with the internal shell morphology revealed by computerised tomography (CT) scanning, enables some emendation of the original description.

Description.

Mean shell height 7.1 mm, with c. 7 whorls, mean shell diameter 2.85 mm (Table 1). Shell cylindrical or subcylindrical, widest at penultimate whorl, apical whorls conical and somewhat more convex than the later ones (see also http://www.morphosource.org/Detail/SpecimenDetail/Show/specimen_id/21851). Protoconch with about 2.5 whorls, protoconch of holotype rather worn, sculpture of the Musake specimen appearing smoothish and glossy, but the eroded suture obscures the transition to the teleoconch; in unworn specimens the transition may be marked by the onset of the subsutural crenulations (as is the case in E. nigeriensis sp. n., described below). Umbilicus closed, not perforate as indicated in the original description. Umbilical region below the basal lip with fine, sharp ribs. Teleoconch fairly smooth with irregular growth lines, at some spots the subsutural crenulations extending into irregular, oblique ribs. Suture deep. The original description mentions the presence of very fine decussations at the third whorl ('tertius subtus lineis tenuissimis, oculo nudo haud conspicuis, decussatus’), which were no longer discernable in the holotype, nor in the better-preserved second specimen. Peristome entire, squarish, slightly higher than wide, palatal wall more or less strongly incurved. Columella appears externally as a slightly widened plate, not bidentate as indicated in the original description. CT scanning shows the columella to be a slightly twisted, slender pilaster with a single small dilatation (Fig. 3H, I). Parietal wall emarginate above the angular tooth. Angular lamella starts at the rear side of the strong and protruding angular tooth (an ad-apertural view (Fig. 3J) provides the suggestion of an initial hairpin turn), and coils regularly inwards for about half a whorl, thereby gradually decreasing in height (Fig. 3I, J). Internal wall of body whorl with two palatal folds. The upper fold strong and very long, running for almost an entire whorl from its starting point above the angular tooth towards the palatal lip of the peristome; its termination is just before (and largely obscured by) the swollen palatal lip. The lower palatal fold is less strong and extends for only about half a whorl, ending well before the peristome (Fig. 3 F–H). Both folds correspond with external depressions on (parts of) the body whorl.

Ecology.

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 ( Jaeckel 1956).