Thursday, 30 August 2007

The Thursday gastropod: Hadra bipartita (expanded)

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.

References
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.

9 comments:

Duncan said...

Imagine a few of those in your lettuce patch :-)

Snail said...

First, your lettuce. Then they'd be in your shopping bags. Then they'd mug you on your way back from the supermarket.

AYDIN ÖRSTAN said...

One of my malacological obsessions is measuring snail shells & not only do I collect snail shells but also their measurements. So, naturally, I am impressed with your "almost 400 shells". What are you going to do with those measurements? Have they been published? If not, would you share the data with me? If you prefer privacy, write to me at: snailstales AT earthlink.net

Snail said...

Aydin, I'd be happy to send you the raw data. It's all on 3x5 file cards ATM (and I'm not sure where I've put them --- I did it all a long time ago) so it'll have to be transcribed again. When I find the cards, I'll let you know.

Anonymous said...

Hi Snail,

Just curious as to your 22.4 mm specimen. I was wondering where that was from as the only ones I am familiar with (including specimens from mission beach, cairns, cooktown and tip of cape york and island ones) all are quite sizable - closer to the maximum dimensions you stated.

Snail said...

That's a good question. Last time I looked at these data was about 10 years ago. I promised Aydin I'd try to find the original info but I haven't located it yet, so I can't check the locality for you.

I've got a plot here of width against height divided into island and mainland populations. Individuals in the island populations tend to be smaller than those on mainland. The v. small one is an island individual but the plot doesn't say from which island. I looked at material from Torres Strait (from Ugar sth to the tip of Cape York), Cairncross Is, Pig Is, Flinders Is, Nymph Is, Lizard Is and Purtaboi Is. I'd suspect that the titchy one came from one of the smaller islands on the NE coast but without the data in from of me, I couldn't tell you which one. If I find the records, I'll let you know. (The data were recorded on cards and I've moved office multiple times since.)

Sorry I can't be much help!

Anonymous said...

Still useful info, thanks.

I do have some Hadras from Murray Is and they are distinctly smaller than the mainland ones although still in the 50 ish sizeclass (from memory).

Anonymous said...

are these snails a bush tucker?

Snail said...

I haven't tried one, but I'm sure there'd be a good lot of meat on that foot.