Gulella davisae, Herbert, 2016

Herbert, David G., 2016, New narrow-range endemic land snails from the sky islands of northern South Africa (Gastropoda: Streptaxidae and Urocyclidae), European Journal of Taxonomy 236, pp. 1-29 : 3-7

Gulella davisae sp. nov.

urn:lsid:zoobank.org:act:DDCAA18B-CC50-4EC1-B63B-28ABAF6904C2

Figs 1–2

Etymology

Named for Linda Davis, manager of the Mollusca collection at the KwaZulu-Natal Museum and a key member of the institution’s malacological field work team.

Material examined

Holotype

SOUTH AFRICA: Mpumalanga, Mariepskop Forest Reserve , 24.56128° S, 30.86367° E, 1700 m, scrubby vegetation between road and forest, in leaf-litter, D. Herbert, L. Davis & M. Cole, stn 14-26, 4 Dec. 2014, height 6.1 mm, diameter 2.9 mm ( NMSA P 0418 / T 4086, dry shell).

Paratypes (listed from north to south)

SOUTH AFRICA: Mpumalanga, same data as holotype ( NMSA P 0245/ T 4088, 5 dry specimens; NHMUK 20160037, one dry specimen; RMNH.5004141, one dry specimen); Mariepskop Forest Reserve, 24.56374° S, 30.86293° E, 1640 m, northern mist-belt forest, in leaf-litter, D. Herbert, L. Davis & M. Cole, stn 14-22, 3 Dec. 2014 ( NMSA P0269/T4090, three dry specimens, one in ethanol); Mariepskop Forest Reserve, 24.56692° S, 30.86482°E, 1520 m, indigenous Afromontane forest, in leaf-litter on forest floor, J.L. Horn, 1 Mar. 2005 ( NMSA W3501/T4087, three dry specimens); Mariepskop Forest Reserve, 24.5679° S, 30.8599° E, 1550 m, northern mist-belt forest, in leaf-litter, D. Herbert, L. Davis & M. Cole, stn 14-26a, 4 Dec. 2014 ( NMSA P0240/T4092, one dry specimen); Mariepskop Forest Reserve, Bushpig Trail, 24.56795° S, 30.86138° E, 1520 m, northern mist-belt forest, in leaf-litter, D. Herbert, L. Davis & M. Cole, stn 14-22a, 3 Dec. 2014 ( NMSA P0262/T4089, one dry specimen); Mariepskop Forest Reserve, Picnic Trail, 24.56847° S, 30.85920° E, 1545 m, northern mist-belt forest, in leaflitter, D. Herbert, L. Davis & M. Cole, stn 14-27, 4 Dec. 2014 ( NMSA P0235/T4091, one dry juvenile specimen); Mariepskop Forest Reserve, east facing slope, 24.57108° S, 30.86014° E, 1519 m, leg. M. Cole, 10 Dec. 2013 ( ELM D17729/T035, one dry specimen); Mariepskop Forest Reserve, in forest beside road at 1520–1700 m, leg. M. Cole, 3–4 Dec. 2014 ( ELM D18022/T036, three dry specimens; ELM W3882/T037, two specimens in ethanol).

Type locality

SOUTH AFRICA: Mpumalanga, Mariepskop Forest Reserve, 24.56128° S, 30.86367° E, 1700 m.

Identification

A moderately sized species of Gulella with a strongly ribbed, cylindrical shell and five-fold apertural dentition including, inter alia, a tricuspid mid-labral complex and a tricuspid columella lamella; also distinctive is the almost complete peristome, interrupted only behind the parietal lamella.

Description

SHELL ( Fig. 1 ). Medium-sized, cylindrical; adult height 5.6–6.3 mm, diameter 2.8–3.0 mm; H:D 1.95– 2.21, with up to 8.0 whorls. Protoconch diameter 1.1–1.3 mm, comprising 1.5–2.0 whorls beyond nucleus, sculptured with fine, close-set axial wrinkles, with an indistinct spiral element appearing in the last halfwhorl; junction with teleoconch distinct. Teleoconch comprising 5.5–6.0 whorls; whorls weakly convex, but usually with a distinct, albeit narrow, shoulder such that suture is indented; sculpture of closeset, prosocline, axial ribs. Aperture roundly quadrate, peristome flaring, almost complete, interrupted only behind parietal lamella; apertural dentition 5-fold ( Fig. 1C ): 1) a strong, vertical, slightly oblique parietal lamella; 2) a large mid-labral complex, itself with three smaller teeth, a simple peg-like upper one and below this a larger, in-running ridge with a large, roundly trigonal tooth at its outer end and a smaller one at its inner end, large outer tooth sometimes with an additional weak cusp on its lower margin; 3) a roundly trigonal basal tooth to left of centre; 4) a more deep-set, transverse, ridge-like, tooth (sometimes with two cusps) between basal tooth and mid-labral complex; 5) a large quadrate columella lamella with three denticles, the upper one usually horizontal and somewhat ridge-like, the middle one protruding furthest into aperture. In addition to the above, there may be a small sinular denticle delimiting a shallow notch behind parietal lamella. Mid-labral complex marked externally by a deep pit behind flared outer lip; a smaller pit underlies basal tooth; columella lip smooth. A juvenile of 2.25 teleoconch whorls exhibited a very small tooth on the upper columella lip and a larger, transverse mid-basal tooth ( Fig. 1E ). Umbilicus open, drop-shaped and of moderate size, opening laterally some distance behind flared columella lip ( Fig. 1D ). Shell milky-white when fresh, usually with some superficial soil debris, particularly in sutural indentation.

LIVING ANIMAL. Head-foot yellow, optic retractor muscles bright orange.

RADULA. A single radula was available; corresponds to ‘Group A’ of Aiken (1981); formula 12 + 1 + 12; length ~ 2.7 mm, with 87 V-shaped rows of teeth; total number of teeth ~2175; rachidian extremely small; inner eight laterals of more or less equal size (3–7 slightly larger) with stout, blade-like cusp; base-plate with an oblique anchoring peg; outer laterals progressively smaller, the twelfth minute.

DISTAL GENITALIA ( Fig. 2 ). Penis of moderate length (~ 3.5 mm), subcylindrical, slightly broader distally, but somewhat constricted at junction with genital atrium; penial retractor undivided and attached to small penial caecum at penis apex. Lumen of penis with a single longitudinal pilaster running from area adjacent to penial caecum to base of penis; also with a raised subcircular pilaster near penis base; remainder of lumen with some weaker longitudinal folds and faint superficial striae; penial armature restricted to a small number of minute, trigonal hooks on apical portion of longitudinal pilaster. Vas deferens inserts laterally about halfway along penis, running toward penis base, then recurving along vagina and fusing with base of spermoviduct; vas deferens loosely adherent to penis base, but not fused to it; no evidence of a penis sheath or epiphallus. Atrium simple; vagina short and thin-walled; duct of gametolytic sac (bursa copulatrix) long, following course of spermoviduct to region of albumen gland; gametolytic sac itself narrow and elongate, scarcely broader than its duct; prostatic and oviductal portions of spermoviduct distinct; proximal portion of reproductive tract damaged and largely missing, but large fertilisation pouch–spermathecal complex remaining.

Distribution

A narrow-range endemic, currently recorded only from Mariepskop Forest Reserve on the edge of the Drakensberg Escarpment in northern Mpumalanga, South Africa; at altitudes from 1520 to 1700 m.

Habitat

Northern mist-belt forest ( Mucina & Rutherford 2006), in leaf-litter.

Remarks

The size and overall facies of the shell is similar to that of G. johannae Bruggen, 2006 from the neighbouring Wolkberg massif. That species, like G. davisae sp. nov., has an almost complete peristome, interrupted only behind the parietal lamella and similar apertural dentition in the juvenile. However, the adult apertural dentition of the present species differs considerably from that of G. johannae . In the latter this dentition is less complex, the mid-labral tooth is essentially a single entity rather than a complex of three denticles, there is no deep-set, ridge-like tooth to the right of the basal tooth and the columella lamella is a simple horizontal tooth. In addition, the shell of G. johannae attains a slightly larger size (height up to 7.7 mm), is somewhat more slender (H:D 2.16–2.88), and the umbilicus is wider and basally orientated. G. vicina luci Bruggen, 1980 , from the eastern highlands of Zimbabwe, also has a ribbed shell and tricuspid labral and columella teeth, but it is larger (height 8–9 mm), has distinct spiral sculpture on the protoconch and its peristome is broadly interrupted in the parietal region.

The almost complete peristome shared by G. davisae sp. nov. and G. johannae is an unusual feature suggesting that the two are closely related and perhaps not members of Gulella s.s. Given that they occur in similar habitats on neighbouring mountain blocks, it seems likely that they are sister taxa derived from an ancestral stock that occurred on both blocks when forest cover was more extensive. G. herberti Bruggen, 2004 , from southern Mpumalanga and Swaziland, is another species with a similar peristome, but its shell is smaller (height ca 4.0 mm) and more globose, has a closed umbilicus and less complex apertural dentition. In G. herberti the peristome is almost completely detached from the preceding whorl, a condition taken to the extreme in G. salpinx Herbert, 2002 from southern KwaZulu-Natal. Herbert (2002) noted the similarities between G. salpinx and the Mascarene genus Microstrophia Möllendorff, 1887 , and Rowson (2010) observed that both possess needle-like spines in the apical part of the penis. Subsequent molecular work ( Rowson & Herbert 2016) has shown that G. salpinx and Microstrophia are indeed related and that they cluster together with species of Primigulella and Dadagulella rather than in Gulella s.l. However, such needle-like penial spines are not evident in G. davisae sp. nov., suggesting that the apertural similarities might be superficial or convergent. The structure of the distal genitalia of G. davisae sp. nov. is unremarkable and is broadly comparable to that of many species of Gulella s.l. Similarly, its ‘Group A’ radula is the most common type of radula in Gulella s.l. and thus neither the radula nor the distal genitalia provide significant data regarding the relationships of the species. Further clarity in this regard must await analysis of molecular data and for the meantime I simply refer the species to Gulella s.l.

Figures

Fig. 1. Gulella davisae sp. nov. A–D. Holotype, height 6.1 mm, diameter 2.9 mm (NMSA P0418/ T4086). E. Juvenile specimen showing apertural dentition, diameter 2.7 mm (paratype, NMSA P0235/ T4091).

Fig. 2. Gulella davisae sp. nov., genitalia, paratype (NMSA P0269/T4090). A. Distal portion of genital system. B. Internal structure of penis.