Hadra bipartita (Férussac 1823) (Camaenidae) is the largest snail species in Queensland's Wet Tropics. How big? I measured almost 400 shells and recorded a range of sizes from 22.4 to 68.3 mm in diameter and 15.8 to 57.3 mm in height. When they're big, they're very, very big; when they're little, they're middling.
The bipartite coloration — light to mid-brown above and dark brown to black below — and the white lip are characteristic. Although a few other species might look vaguely similar, only H. bipartita displays this combination. Occasionally, unicolour specimens turn up. Although they lack the darker base, they invariably have a glossy white lip. (One of these 'blondes' is in the second photo below. It's in the box to the right of my hand.) With much enthusiasm, Pilsbry (1893) gave these variants a name: Chloritis (Hadra) bipartita unicolour.
Because it is so variable in size and shape (some individuals are flatter and have an angled periphery), H. bipartita has attracted a conga line of synonyms. It is likely that H. webbi (Pilsbry 1900) from the Atherton Tablelands and H. semicastanea (Pfeiffer 1849) from Lizard and Restoration Islands also belong to this species. Hadra bartschi (Marshall 1927) from the islands of Torres Strait (between Queensland and Papua New Guinea) is almost certainly a small version of it as well.
Tom Iredale — who wasn't averse to coming up with a new name or two — spoke of the genus Hadra as being 'a source of trouble for local conchologists who attempted to separate the species, using their special knowledge of the actual living conditions' (Iredale 1937: 19). Some years after Marshall split the Torres Strait snails into three species and twelve subspecies (including multiple subspecies from tiny islands), Iredale referred to these taxonomic decisions as 'tragical'. But he hedged his bets and pointed out that, if some of Marshall's taxa were valid, then it was likely that 'many more [names] will also be necessary, as the colonies on each islet appear to differ a little' (Iredale, 1937: 20). Getting into the spirit of things, he then named the population on Warrior Island as a subspecies of Marshall's H. bartschi.
Not only is H. bipartita a big snail, it also has a big distribution. If all those island forms turn out to belong to this species, then it occurs from Torres Strait south to Mission Beach. If they don't, then the northern limit is retracted to the tip of Cape York Peninsula. Hardly a change at all.
It is a rainforest species but lives anywhere with suitable cover. Island populations are not as fussy as the mainland ones: on Lizard Island (NE of Cooktown), it makes do with coastal scrub and grass and on Flinders Island (Princess Charlotte Bay), it copes with eucalypt woodland. It's also quite unconcerned by altitude, being equally happy on the coastal plain and the summit of Queensland's highest peak, Mount Bartle Frere (1586 m).
Although H. bipartita is abundant, live snails are not all that obvious. They rest by day in forest litter, perfectly camouflaged against the dead leaves. They may also burrow. A rainy night in the wet season is the best time to go Hadra-spotting. Otherwise, you'll have to be content with the shards left by pittas and scratched up by scrub fowl.
de Férussac, A.E.J.P.J.F. d'A. (1823) Histoire Naturelle Générale et Particulière des Mollusques Terrestres et Fluviatiles (1819-1851). Paris: J.-B. Baillière, Libraire de l'Academie Naturale de Médecine.
Iredale, T. (1937) A basic list of the land Mollusca of Australia. Pt II. Australian Zoologist 9: 1–39.
Marshall, W.B. (1927) The Australian land shell Thersites bipartita and its allies. Proceedings of the United States National Museum 72: 1–16.
Pfeiffer, L. (1849). Nachtäge zu L. Pfeiffer Monograph Heliceorum. Zeitschrift für Malakozoologie 6: 66–79.
Pilsbry, H.A. (1893). Guide to the study of Helices. Manual of Conchology (2) 9.
Pilsbry, H.A. (1900) A new species of Thersites. Proceedings of the Academy of Natural Sciences of Philadelphia 1899: 473–474.