Rhagada abbasi, Köhler, 2014

Köhler, Frank, 2014, On the land snail Rhagada Albers, 1860 (Gastropoda: Camaenidae) from across the Lesser Sunda Islands, Raffles Bulletin of Zoology 62, pp. 115-123 : 121

Rhagada abbasi n. sp.

( Figs 1 E–H, 2D)

Type locality. Indonesia, Nusa Tenggara Timur Province, Lembata Island (= Lomblem), – 8° 25' S, 123° 28' E .

Holotype. AM C.478280 (dissected specimen, wet).

Paratypes. AM C.471153 (4 wet, 7 dry), AM C.468979 (2 wet, 5 dry), AM C.478281 (50 dry), ZMB 117967 (50 dry) .

Etymology. In honour of John Abbas, Jakarta, who kindly provided material from Lembata and Solor.

Description. Shell moderate in size (D = 15– 15 mm; Table 1 ), broadly subglobose, with variable reddish-brown banding on whitish to creamish background, with sculpture of faint to well-developed axial ribs, umbilicus forming a chink, lip thickened, slightly reflected ( Fig. 1 E–H). Penial verge smooth with pointed tip and well-developed sperm groove, inner penial wall with well-developed longitudinal pilasters, epiphallus with longitudinal pilasters along inner wall, short flagellum ( Fig. 2D ).

Comparative remarks. Shell smaller than R. solorensis , R. floresiana , and R. setzeri setzeri , but similar to. R setzeri atauroensis . Most typical features are smooth penial verge with pointed tip and well-developed longitudinal pilasters of penial wall. Well-differentiated from R. solorensis and R. setzeri in a molecular phylogeny based on mitochondrial COI and 16S sequences ( Fig. 3 ).

Discussion. Previous taxonomic treatments of Lesser Sunda species were predominantly based on shell characters, which were usually inferred from small series of specimens. The better known Australian Rhagada species were shown to have rather conserved shells with regard to general shape and size while exhibiting considerable variation in shell sculpture, umbilical morphology and colour ( Köhler, 2011; Johnson et al., 2012). Extreme amounts of intraspecific variation in shells were observed in some island populations, but are governed by strong selection in an extreme environment ( Stankowski, 2011, 2013). By contrast, the species from the Lesser Sunda Islands remain poorly documented in terms of available study material. However, where large numbers of specimens are available for study (i.e., R. setzeri atauroensis ), the intraspecific variation of shells was found to correspond well with levels observed in Australian species. There is no reason to assume that other Lesser Sunda species exhibit much lower amounts of intraspecific variability. Consequently, traditionally emphasised shell characters, such as sculpture, umbilical morphology and banding pattern, may be of little taxonomic utility.

Recent studies in Australian camaenids, including Rhagada , showed that comparative penial anatomy ( Fig. 2 ) may provide valuable taxonomic information even in species that possess conserved shells (e.g., Köhler & Johnson, 2012; Criscione & Köhler, 2013a, 2013b). The penial anatomy of two already described species ( R. solorensis , R. marghitae ) and two new taxa ( R. setzeri atauroensis n. sp., R. abbasi n. sp.) provided useful taxonomic information complementing the shell-based taxonomy. Molecular phylogenetic analyses based on mitochondrial sequences of the COI and 16S genes showed that Rhagada species from the Lesser Sunda Islands form a clade, which represents the sister group of all known species from the Australian Pilbara region ( Fig. 3 ; Köhler & Criscione, 2013). Amongst these species, R. setzeri atauroensis forms the sister group of R. setzeri setzeri from Alor. Both species are differentiated by mean p-distances of 4% in COI and 2% in 16S ( Table 2 ). Other species are differentiated by p-distances of 11–16% in COI and 8–9% in 16S. These distances correspond well with amounts of interspecific variation found in Australian Rhagada species (about 4%; Johnson et al., 2012) as well as other camaenid genera, such as Exiligada (about 3%; Criscione et al., 2012) and Amplirhagada (about 6%; Köhler & Johnson, 2012). However, extreme intraspecific distances of up to 10% have occasionally also been observed in camaenid snails ( Chiba, 1999; Criscione & Köhler, 2013a).

Progress has been made towards a more complete documentation of the diversity of Rhagada across the Lesser Sunda Islands. However, complete sampling on all Lesser Sunda Islands is required to address the remaining taxonomic issues and to improve our understanding of the evolution of this group throughout the entire archipelago.

Figures

Fig. 1. Shells (1.5× of natural size). A, Rhagada solorensis, Solor Island, AM C.471154; B, Rhagada setzeri setzeri, Alor Island, AM C.471156; C, D, Rhagada setzeri atauroensis n. subsp., Atauro Island: C, Paratype AM C.468711; D, Paratype AM C.468709; E–H, Rhagada abbasi n. sp., Lembata Island: E, Holotype AM C.478280; F–H: Paratypes AM C.471153, showing variation in sculpture and colour pattern. Scale bar = 10 mm.

Fig. 2. Penial anatomy, with penial chamber opened showing internal anatomy. A, Rhagada solorensis, Solor Island, AM C.471154; B, Rhagada marghitae, Nusa Penida AM C.327851; C, Rhagada setzeri atauroensis n. subsp., Atauro Island, holotype AM C.478282; D, Rhagada abbasi n. sp., Lembata Island, holotype AM C.478280. Abbreviations: ep = epiphallus; fl = epiphallic flagellum; gp = genital pore; lwp = longitudinal wall pilaster; pv = penial verge; rm = penial retractor muscle; va = vagina; vd = vas deferens. Scale bars = 2 mm.

Fig. 3. Bayesian consensus phylogram based on analyses of concatenated 16S and COI sequences, adapted from Köhler & Criscione (2013). Lesser Sunda species Rhagada solorensis, R. setzeri setzeri, R. setzeri atauroensis n. subsp., and R. abbasi n. sp. form the sister clade of Rhagada from the Australian Pilbara. Clades from the Australian Kimberley and Pilbara regions collapsed; outgroup pruned from tree; see Köhler & Criscione (2013) for further details.