Zoologische Mededelingen, 81-1 (June 2007)A.C. van Bruggen: Studies on the Streptaxidae (Mollusca: Gastropoda Pulmonata) of Malaŵi 9. Description of Gulella streptostelopsis, a new Streptostele-like species of Gulella 1
Description

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Gulella streptostelopsis spec. nov.

(figs 1-5,6)

Material examined. All material has been derived from leaf litter samples; damaged, subadult and juvenile shells have been expressly excluded from the type material. Localities have been enumerated from south to north (fig. 6).— Malaŵi: (1) Thyolo Dist., Thyolo, Mwalantungi Estate, litter streamhead forest, c. 1100 m, 31.viii.1982, leg. J. Chapman (RMNH 92683, 2 paratypes); (2) Thyolo, Namingombo River, riverine forest litter, c. 1200 m, 8.vi.1980, leg. M (RMNH 92684, 2 paratypes, 2 juv.); (3) Thyolo Mountain Forest on Satemwa Tea Estates, submontane forest remnant, leaf litter, 1300 m, 17.i.2002, leg. K.-D. B. Dijkstra (RMNH 92685, 1 paratype); (4) Blantyre Dist., Blantyre, Soche Mt., submontane litter NE. side, 1400 m, 27.viii.1982, leg. J. Chapman (RMNH 92686, 1 paratype); (5) Blantyre, Soche Mt., leaf litter sites nos. 3-5, 1300-1450 m, 12.iii.1983, leg. M (RMNH 92687, 2 paratypes, 1 juv.); (6) Chiradzulu Dist., Lisau evergreen forest litter, c. 1300 m, ii.1981, leg. J. Chapman [RMNH 92688, 9 paratypes (among which shells shown in figs 1-5; 2 paratypes deposited in IRSNB), 1 subad., 1 juv.; also alc.]; (7) Chiradzulu Dist., Lisau evergreen forest litter, c. 1300 m, 3.i.1982, leg. H. Patel (RMNH 92689, 2 paratypes, 1 damaged shell, 1 subad.); (8) Mulanje Dist., Chigwankhalu Hill, near Malaŵi-Mozambique border just S. of Lake Chilwa, Brachystegia litter, 800-900 m, early May 1983, leg. H. Patel (RMNH, 1 juv.); (9) Zomba Dist., Mpita Forest near Thondwe, leaf litter, c. 1100 m, 10.ii.1982, leg. M (RMNH, 1 damaged adult); (10) Zomba Dist., Zomba, Mulunguzi bridge, Newtonia riverine forest litter, c. 1000 m, 22.iii.1986, leg. M (RMNH 92690, 2 paratypes, 3 subad., 1 damaged subad.); (11) Zomba, Mulunguzi bridge, riverine forest litter, c. 1000 m, 15.xi.1986-25.iii.1987, leg. P. Kamkodo (RMNH 92691, 5 paratypes, of which 1 deposited in MRAC); (12) Zomba-Namitembo road, Namitembo River riverine forest litter, c. 1000 m, 24.iv.1984, leg. M (RMNH 92692, 4 paratypes, 1 juv.); (13) Zomba, forest road, Ficus gulley litter, c. 1100 m, 10.viii.1986, leg. M (RMNH 92693, 12 paratypes, of which 2 deposited in BMNH); (14) Zomba Plateau, below Mulunguzi Dam, riverine forest litter, c. 1450 m, 15.xi.1986-25.iii.1987, leg. P. Kamkodo, type locality (RMNH 92681, holotype; RMNH 92682, 4 paratypes); (15) Zomba Plateau, riverine forest litter below Williams Falls, c. 1500 m, 15.xi.1986-25.iii.1987, leg. P. Kamkodo (RMNH 92694, 1 paratype); (16) Machinga Dist., Chikala Mt., Liwonde, c. 1550 m, 10.xii.1981, leg. J. Chapman (RMNH 92695, 2 paratypes, 1 juv., also alc.); (17) Chikala Mt., saddle on West side, evergreen forest litter, 800-1300 m, c. 2.xii.1982, leg. H. Patel (RMNH 92696, 2 paratypes, 1 subad.); (18) Lilongwe Dist., Dzalanyama submontane forest litter, 1600 m, 17.iii.1984, leg. Dr R.J. Dowsett (RMNH 92697, 1 paratype, 1 subad., 1 juv.); (19) Mangochi Dist., Mangochi Mt., riverine forest litter below Skull Rock, c. 1200 m, 19.iv.1987, leg. M (RMNH 92698, 1 paratype, 2 juv.); (19a) Mangochi Mt., leaf litter near summit, c. 1500 m, 19.vii.1987 (Meredith, in litt., 28.x.2001); (20) Ntchisi Dist., Ntchisi evergreen forest litter, c. 1500 m, iii.1980, leg. M (RMNH, 1 juv.); (21) Mzimba Dist., S. Viphya, Chikangawa Rest House, riverine forest litter, c. 1700 m, vii.1980, leg. M (RMNH 92699, 1 paratype); (22) Nkhata Bay Dist., Viphya, riverine forest litter near Ntungwa, c. 1550 m, 10.vi.1984, leg. M (RMNH 92700, 1 paratype); (23) Kaningina Forest Reserve off Nkhata Bay road, riverine forest litter, c. 1100 m, 5.vi.1986, leg. M (RMNH 92701, 2 paratypes, 1 subad.); (24) Mzimba Dist., Lunyangwa Forest Reserve, riverine forest litter, c. 1300 m, 3.vi.1986, leg. M (RMNH 92702, 1 paratype).
FIG2

Figs 1-5. S.E.M. photographs of two paratypes (nos. 23 and 38 of table 1, both loc. no. 6; RMNH) of Gulella streptostelopsis spec. nov. 1, shell, length 2.37 mm (no. 38); 2, aperture of do.; 3, apex of do.; 4, shell, length 2.21 mm (no. 23); 5, side view of aperture of do. Scale bars 1 mm for figs 1 and 4, 100 μm for figs 2, 3 and 5. S.E.M. photographs by J. Goud (RMNH).

Diagnosis.— A minute species of Gulella s.l., with more or less tapering, almost smooth, shell about three times as long as wide and with three-fold apertural dentition consisting of single angular, labral and columellar processes.

Description.— Shell (figs 1-5) small to minute, clavate, more or less tapering, greatest width well below the middle, always more than two-and-a-half times as long as wide, transparent when fresh to whitish when worn. Umbilicus completely closed. Spire produced, slightly tapering or sides at most subparallel, not convex, apex flattened, obtusely conical to mamillate. Whorls five-and-a-half to just under six, hardly convex, superficially smooth but under high magnification with faint spiral sculpture and growth lines, growth lines turning to weak costulation behind the labrum (fig. 5). Sutures somewhat impressed, fairly shallow, simple and filiform. Aperture (fig. 2) subovate, sometimes distinctly squarish at base, peristome slightly incrassate and reflected, aperture not or hardly obstructed by three-fold dentition: a small angular process (usually a mere swelling), somewhat distant from and therefore not connected with apex of labrum so that there is no sinus; opposite the angular denticle there is an upper labral process in the form of a thickening of the labrum, which process does not correspond to a depression behind the labrum; finally, a very faint thickening of the lower columella may be interpreted as a columellar process.

Measurements of shell: 2.00-2.37 × 0.75-0.81 mm, l/d 2.62-3.17, lw 0.87-1.00 mm, aperture height × major diameter 0.56-0.62 × 0.44-0.50 mm, 5½->5¾ whorls. Holotype shell 2.31 × 0.78 mm, l/d 2.96, lw 1.00 mm, aperture 0.69 × 0.44 mm, >5¾ whorls. Mean values 2.18 × 0.78 mm, l/d 2.89, lw 0.93, aperture 0.59 × 0.47 mm, average values 2.19 × 0.75 mm, l/d 2.92, lw 0.94, aperture 0.59 × 0.44 mm (n = 38).

Animal so far undescribed.

Distribution (fig. 6).— So far only known from Malaŵi, scattered throughout the country south of 11ºS and mainly between 1000 and 1500 m a.s.l.

FIG2

Fig. 6. Map of Malaŵi showing the distribution of Gulella streptostelopsis spec. nov. For numbers refer to ‘Material examined’. The arrow indicates the type locality.

Derivatio nominis.— The epithet streptostelopsis (latinized Greek for Streptostele-like) refers to the likeness to shells of the streptaxid genus Streptostele. The kindred epithet streptosteloides already exists in the family under discussion. The original combination was Opeas streptosteloides Von Martens, 1897, but this taxon appears to be a streptaxid, now named Streptostele streptosteloides (Von Martens, 1897) (vide Verdcourt, 2006; Richardson, 1988; Kabat & Boss, 1997). In view of the similarity of the names and probable causes for confusion in possibly closely allied genera the epithet streptostelopsis is proposed here.