Gulella salpinx, Herbert, 2002

Herbert, D. G., 2002, Gulella salpinx sp. n., a new critically endangered holoendemic species from the limestone deposits of the Marble Delta, KwaZulu- Natal, South Africa (Mollusca: Gastropoda: Streptaxidae), African Invertebrates 43, pp. 1-14 : 2-9

Gulella salpinx sp. n.

( Figs 1–24 )

Diagnosis: Shell of moderate size, length 6.70–7.55 mm, cylindrical to somewhat obovate; sculptured with strong axial ribs; peristome entire and disjunct from preceding whorl, strongly flaring; aperture with a single tooth, a weak in-running parietal lamella;

umbilicus narrow. Radula with relatively few teeth (ca 1750), rachidian present. Penis short and stout, lacking strong spines or hooks, but with three distinct series of minute spinules. Ovoviviparous.

Description: Shell of moderate size for the genus, length 6.70–7.55 mm (mean=7.161, n = 21), width 3.57–3.98 mm (mean = 3.799, n = 21), length/diameter ratio 1.71–2.07; rather variable in shape, from cylindrical ( Fig. 5 ) to obovatecylindrical ( Fig. 6 ), with the broadest part between middle region and apex; diameter of last and penultimate whorls often distinctly smaller than middle whorls. Embryonic shell ( Fig. 14 ) ca 1.6 mm in diameter, comprising ca 2.5 whorls; initial whorl with somewhat irregular wrinkle-like sculpture ( Fig. 15 ), this becoming progressively more radially (axially) aligned in subsequent whorls and appearing as very fine, close-set axial riblets on final embryonic shell whorl; junction between embryonic shell and teleoconch distinct. Teleoconch comprising 6.25–7.00 whorls; whorls moderately to strongly convex, suture indented; sculptured by stronger, prosocline axial ribs, running from suture to suture (55–70 on penultimate whorl); rib intervals lacking obvious microsculpture and with no evidence of spiral threads ( Fig. 13 ); base of juvenile shells lacking axial ribs ( Figs 9, 11 ), sculptured instead by fine, somewhat irregular, raised axial threads ( Fig. 16 ).

Terminal part of last whorl disjunct from preceding whorl and drawn out into a short trumpet-like tube ( Fig. 3 ); length of tube somewhat variable; peristome entire in mature individuals and aperture with only a single tooth, viz.: a simple, rather weak parietal lamella in the form of an in-running ridge, commencing at lip edge and running inward to level of basal part of preceding whorl ( Fig. 7 ); in addition, mid portion of outer lip usually thickened, forming a low bulge one half to two-thirds length of lip from base; peristome at most slightly indented to right of parietal lamella. Interior of aperture appearing smooth, but microscopically sculptured with minute raised granules ( Fig. 12 ). Juveniles lacking apertural dentition at all stages ( Figs 8, 10 ). Exterior of body whorl with a shallow spiral indentation between periphery and base ( Fig. 3 ), giving base a slightly constricted, ‘pinched-in’ appearance; indentation not underlying an inrunning internal palatal ridge/fold, and disappearing immediately behind flaring aperture lip.

Umbilicus open in adult ( Fig. 7 ), but not wide, oval to drop-shaped; much wider and more circular in juvenile specimens ( Figs 9, 11 ); widest in specimens of ca 2.0 teleoconch whorls and constituting 35–45 % of total shell width; umbilical diameter gradually narrowing with the addition of succeeding whorls, from ca 1.2 mm at its widest, to less than 0.5 mm in penultimate whorl.

Shell uniformly white, at most slightly translucent even when fresh; but much of shell surface usually covered with what appears to be a flaky periostracal layer encrusted with microscopic leaf-litter particles. Animal uniformly off-white to pale buff ( Fig. 18 ), somewhat translucent; upper tentacular retractor muscles bright orange, clearly visible through neck and tentacle wall when extended.

Radula ( Figs 19–22 ): Beloglossan, length ca 2.1 mm, with ca 53 broadly v-shaped, transverse rows of backward-pointing teeth; formula (15–17)+1+(15–17); total number of teeth ca 1750. Rachidian tooth present, but small, with a flattened, ovate base plate and a short claw-like cusp ( Fig. 22 ); inner lateral teeth progressively larger, reaching a maximum at teeth four and five (tooth length ca 50 m), then decreasing to less than half this size at edge of radula ( Fig. 20 ); no obvious distinction between lateral and marginal teeth; cusp of larger lateral teeth at least as long as the base plate ( Fig. 21 ), those of inner two and outermost laterals shorter; teeth somewhat curved, the medioventral surface concave, so as to accommodate the inner neighbour when folded ( Fig. 22 ); largest laterals distinctly knife-like in dorsal view. Basal peg anchoring tooth to radula membrane (cf. Aiken 1981) not visible under SEM, but evident in light microscope preparations stained with Shirlastain A.

Genital morphology ( Figs 23, 24 ): The penis is stout and muscular, 1.5–2.0 mm in length (not everted).At its proximal (innermost) end it narrows rapidly toward its junction with the vas deferens, which is terminal and lies at a point adjacent to the insertion of the penial retractor muscle. The latter is undivided and well developed. An epiphallus or epiphalloid sac is not apparent and there is no penial sheath or appendix. The vas deferens is long and sinuous, winding forward beneath and alongside the penis before crossing under the spermathecal duct and free oviduct, after which it passes posteriorly again before joining the free oviduct, approximately halfway between the vagina and the anterior end of the thickened portion of the sperm-oviduct. The distal two-thirds of the vas deferens, nearest to the penis, appears thick-walled and muscular, whilst the proximal third, closest to its junction with the free oviduct, is thinner and more delicate. The spermatheca (bursa copulatrix) is ovate with an orange-brown mass inside. It lies posterior to the beginning of the sperm-oviduct, embedded within the apical viscera; its duct is long, running forward close to the columella and adjacent to the sperm-oviduct, distally it is closely applied to the free oviduct, inserting near to where the latter fuses with the genital atrium. The male and female components of the sperm-oviduct, the spermiduct and the oviductal channel, are separate, the distal part of the oviductal channel being in the form of a uterus, which in some individuals contained 2– 3 eggs /embryos at various stages of development (early summer). The largest observed comprised nearly 2.5 whorls, i.e. almost the entire embryonic shell ( Fig. 17 ).

The internal structure of the penis is complex ( Fig. 24 ). In the proximal (innermost) third the wall is thickened forming an annular pilaster, in the ventral region this continues forward toward the genital atrium as a broad, slightly raised longitudinal ridge. Some variation is evident in the shape of the pilaster and in one specimen part of it was raised, forming a mushroom-like papilla. Penial armature is complex. The bulk of the pilaster bears close-set, elongate-trigonal spinules, mostly directed toward the genital opening. They are relatively easy to pick out on account of their orange colour. Similar, but smaller and more sparsely distributed spinules continue distally along the ventral pilaster ridge. On either side of this, the penial wall bears shallow, irregular longitudinal ridges and lacks spinules.The narrow section of the penis, near its junction with the vas deferens, contains a tuft of elongate fibre glass-like spinules. Between this and the annular pilaster is a zone of extremely small, granule-like spinules. In the everted penis the spines will lie mostly toward the tip of the penis and be directed backwards. These almost certainly function as hold-fast devices during copulation, preventing premature withdrawal of the everted penis from the partner. The elongate spinules near the opening of the vas deferens will presumably project as tuft at the tip of the everted penis.

Type material: Holotype: NMSA V9856 / T1877 , length 7.14 mm, width 3.98 mm. KwaZulu-Natal, Marble Delta, immediately upstream of confluence of Mzimkulu and Mzimkulwana rivers, between Port Shepstone and Oribi Gorge Nature Reserve, on northern bank of Mzimkulu River (30 39.056'S: 30 21.361'E), leg. D. Herbert & M. Bursey, 5.x.2001 and 5.xii.2001.

Paratypes (39): NMSA V9857 / T1878 , same locality as holotype, leg. D. Herbert et al. 05/x/2001 and 05/xii/2001. One paratype from this series has been deposited at each of the following institutions: Nationaal Natuurhistorisch Museum, Leiden ( RMNH 93036 ) ; National Museum of Wales , Cardiff ( NMW Z.2002.055.00001.) ; Natural History Museum , London ( BMNH 20020252 ) ; National Museum of Natural History , Smithsonian Institution, Washington, DC ( USNM 1004625 ) .

Distribution and habitat ( Fig. 1 ): Known only from the type locality which comprises dense valley thicket/woodland, heavily invaded with Chromolaena odorata and Lantana camara . Living under logs and in leaf-litter beneath trees and dense understorey shrubs. All specimens were found in an area approximately 50 m X 20 m. At the time of sampling, the species was moderately common at this locality and shells, both alive and dead, could be found with ease. Standard fertility analysis of soil samples indicate the pH to be 5.9, with a calcium concentration of ca 4000 mg /l.

Etymology: from salpinx (Gr.) f., a trumpet, in reference to the disjunct, flaring peristome.

Figures

Fig. 1. Map of Port Shepstone area and coastal hinterland, showing location of Marble Delta (stippled area). The type locality of Gulella salpinx sp. n. is marked with a black triangle; the cross hatched area indicates the built-up coastal strip.

Figs 2–7. Gulella salpinx sp. n. 2–4. Holotype, length = 7.14mm. 5. Paratype, cylindrical specimen, length = 6.97mm. 6. Paratype, squat, obovate specimen, length = 6.56mm. 7. Paratype, oblique basal view to show umbilicus.

Figs 8–11. Gulella salpinx sp. n. 8–9. Paratype, 4-whorled juvenile, apertural and basal views, diameter 3.40mm. 10–11. Paratype, 7-whorled juvenile, apertural and basal views, diameter 3.78mm.

Figs 12–15. Gulella salpinx sp. n. 12. Paratype, granular microsculpture inside aperture, scale bar = 50 m. 13. Intervals between axial ribs, scale bar = 200 m. 14. Paratype, embryonic shell, scale bar = 0.5 mm. 15. Paratype, first whorl of embryonic shell, scale bar = 200 m.

Figs 16–17. Gulella salpinx sp. n. 16. Axial microsculpture on base of juvenile, scale bar = 100 m. 17. Embryo ex utero, scale bar = 0.5 mm.

Fig. 18. Gulella salpinx sp. n., living animal, shell length ca 7.2 mm.

Figs 19–22. Gulella salpinx sp. n. radula. 19. Active zone of radula at anterior odontophoral flexure, scale bar = 75 m. 20. Half-row of preceding edge of radula folded under and outermost 2–4 teeth not visible, scale bar = 25 m. 21. Zone of lateral maximum, showing basal attachment and elongate shaft/cusp, scale bar = 20 m. 22. Rachidian and shorter, innermost lateral teeth, scale bar = 10 m.

Figs 23–24.Gulella salpinx sp. n. Distal reproductive tract and internal penial armature.23. Distal reproductive tract. 24. Dissection of penis to reveal internal armature; the wall of the penis has been cut longitudinally in the dorso-lateral area and the cut walls spread apart. ap, annular pilaster; atr, atrium; emb, embryo; fov, free oviduct; fst, fibrous spinule tuft; gp, genital pore; gsp, granular spinules; pen, penis; pgl, prostate gland; prm, penial retractor muscle; spc, spermatheca; spcd, spermathecal duct; tsp, trigonal spinules; ute, uterus; vag, vagina; vd, vas deferens; vpr, ventral pilaster ridge.