Tropidophora humbug, Griffiths & Herbert, 2013

Griffiths, O. L. & Herbert, D. G., 2013, New species of land snails (Mollusca: Gastropoda) from two isolated karst formations in central western Madagascar: Tsingy Beanka and Antsingimavo, with additional notes on other regional endemics, African Invertebrates 54 (1), pp. 1-48 : 7-10

Tropidophora humbug sp. n.

Figs 5 , 6 , 25B

Etymology: The colour pattern of bold stripes is reminiscent of that of old-fashioned humbug sweets; used as a noun in apposition.

Diagnosis: Spire very low, shell almost planorboid, body whorl not conspicuously tumescent, umbilicus very wide; columella lip not expanded and not reflected over umbilicus; surface virtually smooth to the naked eye; boldly marked with brown spiral bands on a near white ground.

Description:

Shell: Medium sized, depressed-discoidal to planorboid; spire very low (H:D=0.46– 0.62), often with only embryonic whorls projecting in apertural view; final part of last adult whorl descending prior to aperture, but not steeply so; whorls more or less evenly rounded, suture indented; umbilicus very wide, its margin evenly rounded, underside of embryonic whorls clearly visible. Protoconch of 1¼–1½ whorls, essentially smooth, but microscopically shagreened. Teleoconch of a further 2½–2¾ whorls; the first with approx. 6 weak spiral ridges crossed by numerous fine, close-set, axial threads; spirals becoming more numerous but less distinct on subsequent whorls and axials somewhat coarser; axials resembling fine, uneven, close-set growth-lines on last half-whorl of adult, these extending onto base and into umbilicus; base lacking spiral sculpture. Aperture subcircular, strongly oblique to vertical axis of shell; peristome incomplete, interrupted briefly in parietal region; rim of peristome reflected forming a flaring lip, but this not noticeably enlarged in columella region.

Ground colour bone-white, boldly marked with dark brown spiral bands, the one at and extending just below periphery usually broadest, commonly with 2 or 3 additional bands above and a further 2 or 3 below this; an additional fine orange-brown intermediary spiral line sometimes present in intervals between bands; umbilical region with additional colour bands, often fine, such that base may have up to 7 bands in total; exceptionally, base may have only 1 or 2 colour bands; precise position of colour bands somewhat variable, but uppermost band generally not in contact with suture.

Dimensions: Holotype, max. diameter 31.5 mm, height 16.3 mm; largest specimen, max. diameter 32.0 mm.

External features ( Fig. 25B ): Head-foot more or less uniformly dark grey-brown, but eyestalks and tentacle bases paler; tip of snout conspicuously indented in mid-line; skin texture finely granular.

Operculum ( Fig. 5G ): Oligospiral; exterior portion a calcareous disc, attached to an inner and slightly larger corneous layer; external surface off-white (usually encrusted with detritus particles), lacking colour pattern, but with a broad convex spiral ridge more or less at mid-whorl; thinner toward periphery; edge of disc concave, with numerous, closeset, rather unevenly spaced transverse partitions, except along the growing (parietal) margin, which is smooth.

Radula ( Fig. 6 ): Formula 1+2+1+2+1; length 11 mm, ca 35 rows/mm; dentition fine. Rachidian with seven rounded cusps, central one largest, the outermost pair small; occasionally with very small intermediary teeth between the larger ones. Inner laterals with four cusps, the second of which is bluntly rounded and consistently the largest, the others more pointed; outer lateral with five cusps, the inner one usually slightly larger, the others progressively smaller. Marginal teeth broad, the edge comprising three regions; an inner coarsely dentate element with ca 9 denticles; a more finely denticulate central region, and a smooth outer portion. Such a radula conforms to the pattern seen in Tropidophora (Ligatella) Martens, 1880 (Fischer-Piette et al. 1969).

Holotype: MADAGASCAR: Central W Madagascar, ca 60 km E of Maintirano, tall dense dry forest growing above cliffs on E side of southern Tsingy Beanka at Andohanandranogedro , 18.05028°S 44.53786°E, 380m, iv.2009, R. Randalana, st’n R04/09 ( AMS C.474165).

Paratypes: Same data as holotype ( NMSA L8547 /T2962, 2 specimens) ; st’n 14/95 ( AMS C.469588, 5 specimens) ; st’n 10/96 ( AMS C.469587, 5 specimens) ; st’n 14/96 ( AMS C.469589, 2 specimens) ; st’n 15/96 ( NMSA L8444 /T2658, 6 specimens) ; st’n 03/06 ( NMSA L7042 /T2961, 45 specimens, some in alcohol; MNHN IM-2010-20067, 2 specimens; NHMUK 20120013 , 2 specimens) ; st’n 12/06 ( NMSA L7204 /T2984, 2 specimens) ; st’n R04/09 ( AMS C.469590, 6 specimens; TMAM T166 , 7 specimens) ; st’n R01/10 ( TMAM T160 , 5 specimens) ; st’n R02/10 ( MNHN IM-2010-20068, 7 specimens) .

Additional locality data: Tsingy Beanka : st’ns 05/06, 11/06, 12/06, 13/06, 16/06, 18/06, 01/09, 03/09, 11/09, 03/10, 10/10. Tsingy de Bemaraha: st’ns 08/96, 09/96.

Distribution:A narrow-range endemic; known only from the Tsingy Beanka and Tsingy de Bemaraha, but common at both these localities.

Habitat: Tall semi-deciduous and deciduous western dry forest. Often found on tree trunks after rain. Aestivates in leaf-litter.

Remarks: Fischer-Piette et al. (1993) grouped medium-sized, low-spired Madagascan Tropidophora species together in their ‘groupe d’espèces du T. deshayesiana (Petit de la Saussaye, 1844) ’, but with the exception of T. vittata (Sowerby, 1843) all members of this group have much stronger spiral sculpture than T. humbug , including T. chavani Fischer-Piette, 1949 (see above) with which it is sympatric. Besides being relatively smooth, T. vittata , which is recorded only from north-eastern Madagascar (Fischer-Piette et al. 1993), shares with T. humbug a similarly banded colour pattern and is undoubtedly the most similar species. However, T. vittata has a far more prominent spire, deeper body whorl, narrower umbilicus, and a more extensively flared aperture lip, often with a wide extension in the columella region that partially obscures the umbilicus at full maturity. Fischer-Piette et al. (1993) stated that the holotype of T. vittata was in the NHMUK, but it could not be located there (Ablett in litt. Nov. 2011). T. semidecussata (Pfeiffer, 1847) , is also similar and though a very variable species, like T. vittata , it has a more elevated spire, tumescent body whorl, narrower umbilicus and a more well developed, strongly reflected columella lip.

Specimens of T. humbug from the Tsingy de Bemaraha commonly have a slightly more elevated spire than those from Tsingy Beanka , but H:D ratios for the two populations overlap considerably (H:D=0.47–0.61 compared to 0.46–0.53 respectively).

Figures

Fig.5. Tropidophora humbug sp.n.: (A–C) holotype,Tsingy Beanka,max.diameter 31.5mm,height 16.3 mm, AMS C.474165; (D–F) paratype, heavily banded specimen, Tsingy de Bemaraha, max. diameter 30.4 mm, height 14.1 mm, NMSA L8444/T2658; (G) operculum of holotype, external surface, max. diameter 11.0 mm, AMS C.474165.

Fig.6. Tropidophora humbug sp.n., radula, paratype NMSA L7042/T2961:(A) entire width of radula,scale bar = 250 μm; (B) rachidian and left inner lateral teeth, scale bar = 100 μm; (C) right outer lateral and marginal teeth, scale bar = 100 μm.

Fig. 25. Living animals from Tsingy Beanka: (A) Acroptychia bathiei Fischer-Piette & Bedoucha, 1965, st’n 13/06, shell diameter 23.2 mm, NMSA L7315; (B) Tropidophora humbug sp. n., st’n 12/06, shell diameter 28.3 mm, paratype,NMSA L7204/T2984; (C) Tropidophora secunda Fischer-Piette & Bedoucha, 1965, st’n 03/06, shell diameter approx.19.0 mm; (D) Clavator griffithsjonesi Emberton, 1999, st’n 12/06, shell height 94.8 mm, NMSA L7192; (E) Ampelita milloti Fischer-Piette,1952,st’n 07/09, shell diameter 19.2 mm, NMSA L8502; (F) Ampelita namerokoensis Fischer-Piette, 1952, st’n 12/06, shell diameter 20.3 mm, NMSA L8442; (G) Kalidos griffithshauchleri Emberton, 2002, st’n 12/06, shell diameter approx. 60 mm; (H) Kalidos maryannae sp. n., st’n 12/06, shell diameter 22.5 mm, paratype, NMSA L7193/T2944.