Xanthomelon amurndamilumila, Köhler & Willan & Bourke & Barden & Shea, 2024

Koehler, Frank, Willan, Richard C., Bourke, Adam J., Barden, Paul & Shea, Michael, 2024, A new species of land snail, Xanthomelon amurndamilumila, from the North East Isles off Groote Eylandt (= Ayangkidarrba), Gulf of Carpentaria, Australia (Stylommatophora, Camaenidae), Zoosystematics and Evolution 100 (1), pp. 61-68 : 61

Xanthomelon amurndamilumila sp. nov.

Type locality.

Australia • Northern Territory, Groote Eylandt (= Ayangkidarrba), North East Isles, North East Island (= Amburrkba), 13°38'13.2"S, 136°56'34.5"E.

Holotype NTM P.65134 (1 preserved specimen, dissected, shell broken; Fig. 4 ), from type locality, coll. A.J. Bourke, 18 June 2021.

Paratypes NTM P.62888 (14 preserved specimens; Fig. 5B ), AM C.548628 (4 preserved specimens), from type locality, coll. A.J. Bourke, 18 June 2021.

Additional (non-type) specimens examined.

North East Isles, North East Island (= Amburrkba), NTM P.62774 (59 dried shells), coll. R.C. Willan & A.J. Bourke, 18 June 2021; NTM P.62904 (23 dried shells), coll. R.C. Willan & A.J. Bourke, 18 June 2021; North East Isles, Lane Island (= Milyekaluwakba), NTM P.64715 (4 dried shells), coll. P. Barden, 15 November 2022, NTM P.64717 (7 dried shells), coll. P. Barden, 15 November 2022; North East Isles, Hawk Island (= Ayangkijirumanja), NTM P.62775 (14 dried shells), coll. R.C. Willan & A.J. Bourke, 22 June 2021, P.64716 (1 dried shell), coll. P. Barden, 15 November 2022.

Description.

Shell (Fig. 5 ). Comparatively small for genus (H = 13.6-21.5 mm, D = 15.5-24.2 mm), broadly conical to almost globose in shape, with moderately elevated spire (H/D = 0.81-0.99). Teleoconch entirely covered with well-developed collabral ridges. Whorls with well-rounded periphery, weakly shouldered below well-incised suture. Last whorl rapidly descending just behind aperture; apertural lip thick, slightly reflected, white, parietal wall calloused. Umbilicus narrow, open, partly concealed by reflected columellar lip; collabral ribs ornamented with very small pustules inside umbilical cavity. Shell colour uniform, light brown.

Reproductive anatomy (Fig. 4 ). Penis rather thick, uncoiled, slightly bent, with short epiphallus (shorter than penis), embedded in thin semi-transparent penial sheath; vagina short, thick; bursa copulatrix thick, comparatively short, with bulbous head, extending up to half of spermoviduct; vas deferens thick; proximal part of penial wall thickened, inner penial wall proximally with two smooth pilasters and several strongly developed oblique accessory pilasters, distally with dense pustulation (based on dissections of two specimens).

Etymology.

The specific name for this new species of land snail, Xanthomelon amurndamilumila , comes directly from the Amamalya Ayakwa language spoken by the Anindilyakwa Aboriginal people living on Groote Eylandt and Bickerton Island in the Gulf of Carpentaria. The word, which was provided by the Groote Eylandt Language Centre in consultation with the authors of this paper, means bumpy or corrugated (as in a sheet of corrugated iron) and it is a reference to the regular collabral ribs that ornament the shell. According to the Groote Eylandt Language Centre, the official pronunciation of the word is a-murn-DA-muhluh-muhla. The name is intended as a noun in apposition. Incidentally, Xanthomelon arnhemense , which is the cognate species living on mainland Groote Eylandt, has the Anindilyakwa name of yimurnderrma (pers. comm. P. Barden).

Comparative remarks.

Xanthomelon amurndamilumila differs from other congeners in the Northern Territory by having well-developed collabral ridges (absent in X. interpositum , X. darwinense and X. jannellei ), smaller shell size (larger shells in X. arnhemense , X. durvillii and X. interpositum ) and in relative length of the epiphallus (1.5-5 times longer than penis in X. durvillii , X. arnhemense and X. interpositum ). Furthermore, X. jannellei differs by having an extensive field of pustules on the apical half of the inner penial wall (refer to comparative morphology above for details and to Köhler and Burghardt (2016) for descriptions of other species).

Distribution.

Known to occur only on the three islands comprising the North East Isles - North East Island itself (= Amburrkba), Hawk Island (= Ayangkijirumanja) and Lane Island (= Milyekaluwakba) (Fig. 1 ).

Threatening processes.

The presence of thousands of long dead Xanthomelon shells scattered on the surface across North East Island suggests deleterious changes in vegetation have occurred sometime during the last 100 years. Current inspection of North East Island shows that it is heavily damaged through over-browsing by feral Javan Rusa Deer ( Rusa timorensis ) ( Willan and Bourke 2022). This over-browsing and habitat destruction puts Xanthomelon amurndamilumila potentially at risk of extinction on that island.

Figures

Figure 1. Map of the North East Isles off Groote Eylandt, Arnhem Land, Northern Territory. Specimens of Xanthomelon amurndamilumila sp. nov. have been found on North East Island as well as Hawk and Lane Islands. Small circles indicate sampling sites.

Figure 4. Reproductive anatomy of Xanthomelon amurndamilumila sp. nov., based on dissection of the holotype NTM P. 65134. A Genital system; B Penial interior. Abbreviations used: ag, albumen gland; at, atrium; bc, bursa copulatrix; ep, epiphallus; hd, hermaphroditic duct; ipp, penial wall pilasters, ipw, inner penial wall; p, penis; rm, retractor muscle, so, spermoviduct; va, vagina; vd, vas deferens. Scale bars: 5 mm.

Figure 5. Shell morphology of Xanthomelon amurndamilumila sp. nov. A Living specimen from North East Island, not to scale; B Paratype NTM P. 62888. Scale bar: 10 mm.