Gulella delgada, Muratov, 2010

Muratov, Igor V., 2010, Terrestrial molluscs of Cabo Delgado and adjacent inland areas of north-eastern Mozambique, African Invertebrates 51 (2), pp. 255-255 : 274-277

Gulella delgada sp. n.

Figs 37 , 39–45

Etymology: From Portuguese delgada (slender, elongated) and Cabo Delgado; with reference to the overall appearance of the shell and the name of the type locality.

Diagnosis: Elongated shell with narrow umbilicus and acuminate smooth apex; with large, widely spaced axial ribs on teleoconch; large short parietal lamella, long palatal lamella (which consists of low distal and large proximal parts), small columellar cusp and large, obtuse, rounded, deeply set columellar tooth.

Description:

Shell semi-translucent, white, elongated acuminate-ovate, with narrow umbilicus and acute apex. Protoconch (~2.5 whorls) smooth. Teleoconch consists of 4–5 convex whorls, slightly angulated above the periphery, separated by deep suture; with strong, widely spaced axial ribs accentuated just above the periphery of the whorls and less developed above the aperture (width of ribs on average three times less than width of intercostal spaces). Last whorl not ascending towards apex, height is less than half (about 45%) of shell height. Aperture oval, with very narrowly reflected columellar, basal and palatal margins, incised just below the suture of preceding whorl in the area of pneumostome. Apertural dentition of (1 st) large parietal lamella that suddenly starts a short distance forward of columellar plane, very slightly curves towards the area of pneumostome and reaches apertural edge; (2 nd) palatal lamella about half a whorl long, reaches apertural margin, low in its first half, then suddenly becomes the same size as parietal lamella in the same area where parietal lamella starts (distal portion of palatal lamella is cross-symmetrical with parietal lamella); (3 d) basal lamella low, about a quarter of a whorl long, situated closer to columella, ascends towards small columellar cusp and gradually disappears a short distance from it; (4 th) small columellar cusp positioned about two-thirds of distance between columellar edge and large, obtuse, rounded, deeply set (5 th) columellar tooth. Juvenile with small parietal tooth, large basal lamella (positioned parallel to basal edge of aperture) and slight thickening in middle of columella. No internal dentition in upper whorls.

Measurements of the shells: 1 st syntype: 7.5 whorls, height 4.0 mm, major diameter 1.8 mm; 2 nd syntype: 6.5 whorls, height 3.8 mm, major diameter 1.8 mm; 3 rd syntype (juvenile): 5.5 whorls, height 2.7 mm, major diameter 1.8 mm.

Type material: 1 st syntype ( MNHN: 23097), 2 nd syntype ( NMSA: L8003 / T2583 ), 3 rd syntype (juvenile) ( NMSA: L8004 / T2584 ); all from MOZAMBIQUE: Cabo Delgado: 1.1 km WNW of lighthouse, 19 km NE of Palma , 10.68883°S: 40.62806°E, alt. 11 m, 24 xi.2009, I. V. Muratov .

Distribution: Known so far only from the type locality in north-eastern Mozambique.

Remarks: Designation of syntypes is necessary because of significant differences in the dentition of the adult and juvenile shell. All three shells are worn, without any periostracum. The larger adult (1 st syntype – Figs 37 , 39–43 ) has a slightly bent shell axis in the area of the third whorl, which is not the case in the other two shells. The smaller adult (2 nd syntype – Fig. 44 ) and the juvenile (3 rd syntype – Fig. 45 ) both have two large holes at the back of the shell as the result of pre-collection damage.

There are four other species currently in the genus Gulella with an acuminate apex and similar dentition: Pupa minuscula described by Morelet (1877: 340, pl. 12, fig. 5; 3× 2 mm) from Anjouan, Comoros, Ennea radius described by Preston (1910: 529, fig. 8; 3.25×2.00 mm) from the Shimba Hills in south-eastern Kenya, Gulella cuspidata described by Verdcourt (1962: 3, 27; pl. 3, fig. 2; 4.8× 2.5 mm) from the Usambara Mountains in north-eastern Tanzania and Gulella browni described by van Bruggen (1969: 69, figs 25–26; 3.0× 1.7 mm) from the east shore of Lake Sibayi in northern KwaZulu-Natal. G. delgada differs from all four by the more elongated shell with wider spaced axial ribs on teleoconch, as well as by the much longer palatal and basal teeth.

Figures

Figs 30–38.Streptaxidae:(30) Edentulina affinis,33.4×17.6 mm,stn 5; (31) Taylorialeroyi, 14.4×21.0 mm, stn 5; (32) Gonaxis cf. percivali, 9.4×6.9 mm, stn 1; (33) G. denticulatus, 7.0×4.6 mm, stn 11; (34) Gulella sexdentata var. liederi, 9.4×4.8 mm, stn 1; (35) G. subhyalina, 6.5×2.3 mm, stn 1; (36) G. perissodonta, 3.2×1.5 mm, stn 7; (37) Gulella delgada sp. n., 4.0×1.8 mm, 1st syntype, stn 7; (38) Streptostele herma, 3.8×1.2 mm, stn 7. Scale bar 10 mm in Figs 30–31; 3 mm in Figs 32–34; 1 mm in Figs 35–38.

Figs 39–45. Gulella delgada sp.n., stn 7: (39–43) 1st syntype, 4.0×1.8 mm, five views; (44) 2nd syntype, 3.8×1.8 mm; (45) 3rd syntype, 2.7×1.8 mm.