Tylomelania sinabartfeldi, Rintelen, Thomas Von & Glaubrecht, Matthias, 2008

Rintelen, Thomas Von & Glaubrecht, Matthias, 2008, Three new species of the freshwater snail genus Tylomelania (Caenogastropoda: Pachychilidae) from the Malili lake system, Sulawesi, Indonesia, Zootaxa 1852, pp. 37-49 : 42-45

Tylomelania sinabartfeldi sp. nov.

Type material. Indonesia, Sulawesi, Larona River: Holotype ( Fig. 4 A; 24.0 mm x 18.5 mm, loc. 58-99), MZB Gst. 12.112; paratypes ( Fig. 4 B): loc. 58-99, MZB Gst. 12.113, n=53; ZMB Moll. 108315, n=65; loc. 71-02, ZMB Moll. 112690, n=2; loc. 58-99 (leg. Rainer Masche 2007), ZMB Moll. 192697, n=3.

Etymology. The new species has been named sinabartfeldi in honour of Sina Bartfeld, who contributed to supporting malacological research.

Description. Shell ( Fig. 4 A,B): Medium sized, brown, two shapes: conic or subglobose, transitory forms exist. Spire angle 45–85°. Top whorls in adult specimens always corroded to a varying degree, 3–6 remaining whorls, can reach up to 27.2 mm ( Tab. 2 ). With spiral ribs only. Aperture oval, pointed at top and slightly siphonated at base. Columella and interior brown.

TABLE 3. Embryonic shell parameters of Malili lake system Tylomelania . Values represent, from top, range, mean and standard deviation, and sample size. juv.—juveniles in broodpouch; h max—embryo shell height; ax 3rd—axial ribs on third whorl; n.a.—not applicable.

External morphology: Headfoot black, mantle edge serrated to a varying degree. Body coiled in 2.5 whorls.

Operculum ( Fig. 4 C): roundly-ovate, last whorl inflated, multispiral with 4–5 whorls. Radula ( Fig. 5 A–D): 176–231 rows, 18.9–25.5 mm long, on average 9.6 teeth per mm (n=9). Central tooth with very large and almost squarish major denticle and two minor denticles on each side. Glabella with slightly rounded base. Lateral teeth with very much enlarged squarish major denticles and two minor denticles on each side. Marginal teeth shovel-like, inner and outer marginals with three denticles each, the outermost ones considerably wider than the inner ones. Inner marginals larger than outer ones.

Reproductive biology: Brood pouch contains 11–67 embryos, their size can reach 5.0 mm (Tab. 3). Embryonic shells ( Fig. 5 E–K): Conic, with no or few and comparatively weak axial ribs emerging on the 2nd whorl and fading on the 3rd whorl (Tab. 3).

Distribution and habitat. South Sulawesi, lower reaches of Larona River ( Fig. 1 B).

On submerged logs exposed to strong current, collected in 0.1–1 m depth. As with T. baskasti , the inaccessibility of deeper parts of the river because of the strong currents does not allow us to estimate its depth range with any certainty.

Taxonomic remarks. The two extremely distinct shell forms encountered in this species are suggestive of two morphs or even two taxa at first glance. A comparison of the entire series revealed transitions between both forms, though, and as a consequence an attempt to unambiguously sort the sample into the two forms failed (compare Fig. 4 ). Radula and embryonic shell comparisons between specimens chosen from both extremes of shell form also failed to show any difference ( Fig. 5 ) and both forms were sampled from the same log without any observable difference in distribution. We thus suggest that T. sinabartfeldi as described here represents one highly variable species with respect to shell form. If this variability is an expression of ecophenotypic variation remains open to speculation at this point.

Despite the high intraspecific variability in shell shape, both the subglobose and conic form of T. sinabartfeldi do not resemble any other species of Tylomelania .

Figures

FIGURE 1. Sulawesi and the Malili lake system with sample sites. Locality numbers are the original field numbers and correspond to those in Tab. 1.

FIGURE 4. T. sinabartfeldi sp. nov. (loc. 58 - 99). A – D. shells, A. holotype, MZB Gst. 12.112, B. paratypes, ZMB Moll. 108315. Scale bar = 1 cm. C. opercula, ZMB Moll. 108315. Scale bar = 0.5 cm.

FIGURE 5. T. sinabartfeldi sp. nov., ZMB Moll. 108315 (loc. 58 - 99). A – D. radula, A, B, keeled shell morph, A. segment, frontal, B. segment, apical (45 °); C, D. round shell morph, C. segment, frontal, D. segment, apical (45 °). Scale bar = 0.1 mm. E – K. embryonic shells, E – G, round shell morph, E. lateral view, F. apical whorls, lateral, G. apical view; H – K, keeled shell morph, H. lateral view, I. apical whorls, lateral, K. apical view. Scale bar = 0.5 mm.

Tables

TABLE 2. Shell parameters of the three new species. Values represent, from top, range, mean and standard deviation, and sample size. h—shell height; w—shell width; aph—aperture length; apw—aperture width; bwl—body whorl; angle—spire angle; n. a. — not applicable.

Species	h (mm)	w (mm)	aph (mm)	apw (mm)	bwl (mm)	whorls (N)	angle (°)	axial ribs (N, on bwl)
T. baskasti	9.5–54.7 37.47 ± 9.864 69	4.2–18.1 13.84 ± 2.794 69	4.2–16.0 11.70 ± 2.481 69	2.1–9.4 7.00 ± 1.424 69	6.2–25.8 19.04 ± 4.284 69	4–9 7.1 ± 1.31 69	13–25 20.4 ± 2.51 67	n.a.
T. sinabartfeldi	14.4–27.2 20.86 ± 2.499 118	10.6–20.8 16.40 ± 1.754 118	8.3–14.0 10.92 ± 1.107 118	4.9–9.4 7.26 ± 0.801 118	11.1–23.7 16.70 ± 2.180 118	3–6 4.5 ± 0.90 118	45–85 63.5 ± 6.80 112	n.a.
T. hannelorae	10.6–13.9 12.31 ± 1.022 9	5.5–6.8 5.91 ± 0.398 9	3.9–4.6 4.3 ± 0.254 9	2.3–2.7 2.57 ± 0.138 9	6.9–7.9 7.34 ± 0.375 9	3–5 4.3 ± 0.71 9	11–17 13.3 ± 2.00 9	15–21 17.7 ± 2.19 8