Gulella ndiwenyiensis, B & Rowson & C & N & Lange, 2007

B, Rowson, C, N & Lange, 2007, Two new species of Gulella (Mollusca Pulmonata: Streptaxidae) from the Taita Hills Kenya, African Invertebrates 48 (2), pp. 21-32 : 22-27

Gulella ndiwenyiensis sp. n.

Figs 1–3 , 8–13

Etymology: From the type locality, Ndiwenyi Forest Reserve.

Diagnosis: Shell medium-sized for the genus, distinctively ovate-barrel-shaped; sculptured with oblique axial ribs; peristome complete, apertural dentition five-fold: a strong, slightly sinuous parietal lamella, two palatal processes, a basal process and a strong columellar tooth; embryonic shell finely granular; umbilicus open, deep.

Description: Adult shell ( Figs 1–3 ) medium-sized for the genus (height 4.7–5.3 mm, width 2.7–3.3 mm), and ovate-barrel-shaped, of 6.25 to 6.75 whorls. Intraspecific variation in shell shape moderate. Penultimate whorl and body whorl together comprise about 68% of total shell height. Aperture (including peristome) comprises about 36%

of total shell height. Peristome complete, thickened and reflected and flaring, particularly in palatal and basal part. Body whorl only slightly constricted adjacent to the aperture. Umbilicus open, wide, and tubular; columella relatively straight. Apertural dentition moderately developed, consistently with five processes as follows: (1) a large, thick, slightly sinuous and deeply entering parietal lamella projecting outwards a short distance from the body whorl and corresponding to an outwardly and palatally directed V-shaped depression in the parietal callus; (2) a small, rounded, boss-like upper palatal tooth, in some specimens taking the form of a rounded, very short lamella shallowly entering; (3) a small, rounded, short lower palatal lamella shallowly entering; (4) a small, slight, narrow, transverse basal lamella set closer to the outside of the aperture than the other teeth; and (5) a moderate, rounded, boss-like columellar tooth. Resulting apertural dentition formula sensu Verdcourt (1962) is 1; 2; 1; 1. Parieto-palatal sinus wide, simple. Parietal callus moderately thick and clearly distinct from body whorl. Outer palatal wall with two, relatively slight, excisions corresponding to the palatal teeth. Outer columellar wall with a relatively slight excision corresponding to the columellar tooth. No sign of juvenile dentition in the single juvenile specimen (paratype 3) or inside the shells of dissected adults. Shell colourless and glassy, dirty white when corroded, with no obvious periostracum. Shell surface as follows: embryonic whorls smoothly, irregularly granular with very faint and irregular spiral scratches under a light microscope (60× magnification). Later whorls with major sculpture of oblique, straight, regular axial ribs which, though distinct, do not have sharp edges where they contact the shell surface and thus appear slightly smoothed. On the holotype, these ribs occur at a density of about 8 per mm (penultimate whorl), about 9 per mm (body whorl), and increase in density while decreasing in size towards the aperture on the last half of the body whorl, where they also become less regular and in some cases slightly sinuous. On the later whorls of some specimens, including the holotype, the ribs are interrupted by 1–3 very irregular spiral depressions, each about the width of one of the largest ribs and continuing for irregular distances around the whorls.

Body colour: Alcohol-preserved specimens are nearly unicolorous tan-cream, without differently coloured tentacles, patterning on the mantle, etc. The digestive gland is tanbrown in colour.

Salivary gland ( Fig. 8 ): Single, 2.75 mm long, not folded, fragile, bicolorous (cream with white regions surrounding entry of both salivary ducts).Anterior duct exiting gland subapically; posterior duct exiting just posterior to the midpoint of gland. Both salivary ducts substantially thickened and rounded prior to point of entry into buccal mass, becoming narrower and flattened at point of entry.

Genitalia ( Figs 9–13 ): Penis notably long (6.40 mm when straightened, or 0.75 whorls when bent) and further lengthened by running in a single, complete, tight loop just proximal to the midpoint. Penis with a short, bud-like penial appendix very apically. Whole of penis and distal part of vas deferens enclosed in a thin, slightly wrinkled, elastic, transparent sheath, this sheath enclosing the complete loop in the penis in a straight path rather than following the penis’ path through the loop. Sheath perhaps contiguous with penis wall at both apical and basal ends of the penis, but this is difficult to determine by dissection alone. Sheath with two short basal retractor muscles, originating from the body wall. Vas deferens flattened, uniformly thick throughout its length, with lumen clearly visible from outside, entering penis apically, with thick penial retractor muscle attaching to both penis and vas deferens around the entry point. Penial retractor originating from the free muscle system and not from the body wall. Interior surface of penis ( Fig. 11 ) consisting mainly of serially repeating prism-shaped pads bearing chitinous spines or hooks as follows. Apical part of penis: small, rounded, flat, scalelike pads, most bearing single, minute, simple yellow-brown triangular hooks (about 0.05 mm long). Penial appendix: without hooks but containing a single, very large (0.60 mm long), curved red-brown spine, slightly sinuous in one plane, attached firmly to end wall of appendix with its point projecting a short distance into main lumen of penis. Middle part of penis, incorporating loop: larger, irregular, raised prism-shaped pads, most bearing single, slightly recurved and slightly blunted yellow-brown triangular hooks, which vary little in length (about 0.03 mm long). Basal part of penis: more regular, evenly spaced, uniform, elongate-columnar prismatic pads projecting into the lumen, each bearing single, minute, simple yellow-brown triangular hooks (about 0.02 mm long), this pattern continuing as far as the entry of the penis into the atrium. Total number of hooks in penis: about 300. Albumen gland moderately sized and with a uniform structure of small and indistinct vesicles or acini. Hermaphroditic duct diverticulum (talon) enlarged, but compact and convoluted, not hidden within albumen gland. Bursa copulatrix (= gametolytic sac or spermatheca) oval, apparently empty, and attending albumen gland. Acini of oviductal gland elongate, flattened, distinct and relatively large. Acini of prostate small and indistinct. Oviparous or ovoviviparous (oviduct of paratype 2 contains a single, large, rounded-reniform egg with soft membrane containing calcite crystals and without obvious internal structures). Walls of oviduct thin, stretching to accommodate the egg in paratype 2 and folded, collapsed and slightly torn in paratype 1, which we presume to have recently laid an egg. Vagina and atrium short, little muscularised.

Holotype: KENYA: Taita Hills, Ndiwenyi Forest Reserve (3°26'S: 38°21'E), leaf litter in indigenous forest at 1580 m altitude, leg. C.N. Lange, 26.ix.1998 ( NMK).

Paratypes: Collection data for all paratypes same as holotype; all specimens except paratype 3 and paratype 13 are live-collected adults (Table 1).

Other material examined: 31 additional specimens, as follows: KENYA: Taita Hills: 1 adult, Ndiwenyi Forest Reserve (3°26'S: 38°21'E), leaf litter in indigenous forest at 1580 m altitude, leg. C.N. Lange, 26.ix.1998 ; 2 adults, Mbololo Forest Reserve (3°20'S: 38°26'E), leaf litter in indigenous forest at 1800– 2200 m altitude, leg. C.N. Lange, 1.x.1998 ; 15 adults, Macha Forest Reserve (3°27'S: 38°22'E), leaf litter in indigenous forest at 1550 m altitude, leg. C.N. Lange, 27.ix.1998 ; 13 adults, Kichuchenyi Forest Reserve (3°25'S: 38°21'E), leaf litter in indigenous forest at 1450 m altitude, leg. C.N. Lange, 28.ix.1998 ( NMK) .

Remarks: We consider this species readily distinguishable from all other East African Gulella by the combination of macroscopic shell characters. The general features of the shell, including the five-fold apertural dentition, strongly suggest inclusion in Gulella L. Pfeiffer, 1856 s. l. rather than any other genus as currently recognised. However, new streptaxid species from Africa and associated islands continue to be attributed to the genus Gulella while it is widely acknowledged that the taxonomy of the genus is unsatisfactory (e.g. Schileyko 2000). Subgenera and sections are currently of limited value and we refrain from assigning G. ndiwenyiensis to any of these, although we do not believe that this species represents a new group. We also consider that although Schileyko (2000) and others have erected subfamilies of the Streptaxidae that take into account shell and other characters, it is likely that Gulella s. l. may prove heterogenous enough to challenge these classifications. Therefore we do not at this point assign this species to any subfamily.

The presence and nature of the penial appendix and interior penial hooks resemble in some respects members of the subgenus (or section) Primigulella Pilsbry, 1919 (data tabulated by Verdcourt 1990) although the general form of the shell is substantially different. A penial appendix containing a spine, as opposed to a massive hook, is a feature of certain other East African streptaxids, including edentate, much larger species in the genus Gonaxis Taylor, 1877 s. l. (BR unpublished data). It does not, however, closely resemble the appendix of any of the West African species illustrated by Degner (1934) or those for which data are available from other regions. We therefore tentatively conclude that the nearest extant relatives of G. ndiwenyiensis are East African. The presence of this feature in groups with very dissimilar shells suggests that, whether homologous or not, further systematic work is required to understand its evolutionary significance and importance in biogeography.

Figures

Figs 1–7. New Gulella species from Kenya: (1–3) G. ndiwenyiensis sp. n., holotype shell, length 4.9 mm; (4–7) G. nictitans sp. n.: (4–6) holotype shell (length 3.8 mm), (7) aperture of paratype 1.

Figs 8–13. Gulella ndiwenyiensis sp. n., anatomy of paratype 1: (8) salivary gland from columellar side; (9) penis from ventral side; (10) genitalia from dorsal side; (11) penis opened from dorsal side; (12, 13) views of interior surface of penis, greatly enlarged.Abbreviations: bc – bursa copulatrix, bsr – basal sheath retractor muscle, p – penis, pa – penial appendix, prm – penial retractor muscle, ps – penial sheath, sgd – salivary gland duct, v – vagina, vd – vas deferens.