15 January 2009

Reverend Lowe's snails

Richard Thomas Lowe (1802-1874) was a British clergyman naturalist. He studied plants, fishes and snails, of course. I was at the Smithsonian's National Museum of Natural History in D.C. today and copied one of Lowe's papers on some of my favorite coastal snails, Melampus and Truncatella. The paper, titled "On the Genera Melampus, Pedipes and Truncatella: with Experiments tending to demonstrate the real nature of the Respiratory Organs in these Mollusca", came out in 1832 in the Zoological Journal.

Those were the formative years of malacology when even the broadest classifications of most of the mollusc species were debatable. Thus, in his paper Lowe was concerned with the question of whether Melampus and Truncatella were in the order Pectinibranchia or the Pulmonea. The former encompassed all the snails with gills, while the latter those with lungs. A simple dissection would have provided the answer, but "...the small size of the species, not to mention want of instruments and skill in the dissector" forced Lowe to resort to a series of experiments almost all of which involved the keeping of the subject snails in sea or fresh water or outside of water for various periods.

LowesExperiment

Not surprisingly, Lowe's experiments produced contradictory and puzzling results: both Melampus and Truncatella survived outside of water in wet containers, while when forced to remain in sea water they sometimes remained alive, sometimes died. At the end, however, he concluded that both genera were marine pectinibranchs.

Lowe didn't realize that the truth was a bit more complicated and, at the same time, much more interesting than his simple experiments could reveal. Truncatella breathes with a gill (see my dissection here), but lives its entire life on land near the sea, while Melampus breathes with a lung, lives at the edge of the sea, but enters it to reproduce via planktonic veliger larvae.

What we see in the case of Melampus and Truncatella is a mosaic-like pattern of mixed anatomies and lifestyles often observed during evolutionary transitions from one habitat to a drastically different one. The good ol' reverend was in for a surprise.

LowesPlate
The plate from Lowe's paper showing the snails he studied: 1-7, Melampus; 8-12, Pedipes; 13-18, Truncatella.

1 comment:

Eric Heupel said...

That is really too beautiful and cool. Two land snails - one with gills, that lays eggs, another with lungs that retains the planktonic larvae!

Viva La Evolución!!