14 January 2010

A forgotten thesis on Rumina decollata

While searching for records of the European land snail Rumina decollata from Arizona, I found a master's thesis from 1951 entitled Anatomy and life cycle of the snail, Rumina decollata.

Because of my interest in the genus Rumina, I downloaded the thesis and quickly skimmed thru it. If 2 blank pages, 2 title pages, table of contents, etc., are excluded, it's only 29 double-spaced pages. I am surprised that some one actually earned a master's degree in 1951 studying the anatomy of Rumina decollata, because Pilsbry had already published descriptions and drawings of the anatomy of the same species in the Manual of Conchology in 1905 (cited in the thesis) and then in his Land Mollusca of North America in 1946 (not cited in the thesis) and Wille had also done the same in 1915 (Jenaische Zeitschrift Naturwissenschaft 53:717-804) (not cited in the thesis).

But, anyway, here are some interesting tidbits from the thesis.

The author states that in the wild "the snails feed upon living vegetable matter". Rumina decollata is actually known to be an omnivore, eating plant matter and also preying on live snails. Here is another sentence: "The epiphragma [epiphragm] is essentially a layer of dried slime, supplemented and strengthened by the addition of calcium phosphate". It is calcium carbonate.

A noteworthy claim: "Muscular contraction and relaxation [of the floor of the mantle cavity] result in the change in size of the cavity, with resultant intake and expulsion of air". Unfortunately, nothing more is said on this and it is not explained if and how the author observed this or if she was repeating something read in the literature without giving a citation. Here is a related post.

The most useful section in the thesis is the one about the reproduction of Rumina decollata, especially the following paragraph:

There is reciprocal fertilization, that is mutual impregnation, preceded by a preparatory event in which two snails approach each other and evert the genital atrium. Copulation occurs in forty to sixty seconds. Copulation of snails in this collection began in the middle of September and continued for a period of three weeks. After copulation occurred, the snails were isolated and each was found to produce numerous clutches of eggs.
From this we can deduce that mating was in the face-to-face position* in agreement with the mating of Rumina saharica (see my paper here). Moreover, because both mated individuals laid eggs, sperm exchange appears to have been reciprocal.

Here is Plate I from the thesis with the drawings of a live snail and shells. Will the readers notice what is wrong with these drawings?


The figures were reversed during printing and consequently, the shells ended up sinistral. No, the author did not happen to have chanced upon a colony of reverse-coiled snails, because she does indicate that the shell of Rumina saharica is "spirally coiled to the right", that is, her specimens were indeed dextral. Another indication that the figures were reversed is that the shell labeled "ventral" is actually showing the dorsal side and vice versa.

A paper based on this thesis was published in 1957 (Batts, J. H. 1957. Anatomy and life cycle of the snail Rumina decollata (Pulmonata: Achatinidae). Southwestern Naturalist 2:74-82). The drawings in the paper were still reversed!

*Because the snails approached each other. If they had mated by shell-mounting, one would have climbed on the shell of the other.


bev said...

This afternoon, I took one of my dogs for a walk for a few blocks through town. I made a point of studying gardens along the sidewalks. The vegetation is now mostly dried up, so it was easy to spot snail shells. I found these shells in just about every garden after just a few seconds of scanning the soil surface. My conclusion is that Bisbee must be full of these fellows!

Edward Baker said...

I am currently writing a short paper on keeping this species in captivity as it has been kept by people interested in 'invertebrate 'pets' several times in the UK (and I have a small culture of it).

Any good references?


Bev: hopefully they are keeping the Helix aspersa population under control.

Ed: about 10 yrs ago I kept them in captivity for a year or so. Let me go thru my notes first & then I'll write to you in detail.

bev said...

As a matter of fact, they probably are. Yesterday's walk was in the company of one of my neighbours who lives in the canyon below my place. I questioned her about land snails in her garden. She says that, until a few years ago, the H. aspersa snails were so plentiful that they had to remove them from the garden (quite literally) by the bucketful. Several years ago, a neighbour's visitor from Europe even came by and removed a good many to cook while in Bisbee. In recent years, they have noticed that there are almost none. They attributed the disappearance to the recent drought years, but she had also noticed the elongated shells around - not before, but more recently - but had not given that much thought. So, drought or R. decollata - something has resulted in the severe decline of H. aspersa in her garden. I will continue to do more checking around town for land snails. One place I thought might be worthy of exploration is the concrete storm canal system that runs below the sidewalks and streets in much of the town - it handles the massive amounts of water run off that can happen during the summer storms. I'll look for a couple of access points and maybe go for a walk along them to see what kind of drift might be found.

Edward Baker said...


Orlando said...

This thesis was a very nice found! Thanks for sharing it and the nice comments about it. Probably it'll be important to my work.