What's The Predator That Drills Holes On Bivalves?

[Pagurus]

Steve,

That clamshell has a bit of brown seaweed stuck to it, so it might look worse than it really is. The shell is somewhat worn though. These softshell steamer clams (Mya arenaria) spend most of their lives under the abrasive sand and they do wear down a bit. The shell in the photo probably became a little more worn than usual, living in the course gravel in my tank. The empty shell, after the clam was eaten, probably took a little beating from some of the other animals in the tank before I removed it.

The Moon snails plough through the sand, often buried beneath the surface, until they find a tasty mollusc. The snail envelops its prey with it's huge slimy foot, larger in diameter than the snail's own shell, and then it begins its boring work.

The imperfect shape of the hole in the bivalve clam might be partly due to the gravel substrate in my aquarium, or maybe the jostling of the moon snail by its tankmates while it was attempting to eat it's dinner. Usually the holes are rounder, even in my aquaria.

In answer to your question, I did not observe the snail in the photo being eaten by another moon snail. However, the beach where I found it has a fairly large population of live moon snails and no other snails large enough to make a hole this big. I am certain it was made by a moon snail. I commonly find smaller predatory gastropods on the nearby rocks, especially the dog whelk, Nucella lapillus, but they make a much smaller hole, and they rarely venture into the moon snail's sandy habitat.

I wouldn't be surprised if the gastropod you're looking for is a member of the genus Polinices, but I don't know enough to be sure. I would love to know what you discover. Thanks for bringing up this subject. I will be sure to look for fossil bivalves with these boring holes. Of course, not all the holes in the shells, fossil or otherwise, will be from predatory gastropods. I'm sure yours are, from your description, but many holes will be caused by boring sponges. I've found quite a few fossil oysters (Exogyra, I think) from New Jersey with holes that look like they were made by sponges. Does anyone know if there are fossil sponges? I expect their spicules would fossilize, but those are awfully tiny. I will stop rambling now. Good luck with your research.

Mike G

[Terry Dactyll]

It is very interesting...Is there any consistency to the position of the borings on the different species of shells... Usually predators hone their technique over time to achieve optimum effect for the minimum of effort?

[Pagurus]

It is very interesting...Is there any consistency to the position of the borings on the different species of shells... Usually predators hone their technique over time to achieve optimum effect for the minimum of effort?

That's an excellent point, Terry. The research seems to be inconclusive. There have been some very good studies done on the position of the bore holes on the shell of the prey, with detailed analysis. The predatory snails seem to have a slight preference in many cases, but the evidence isn't overwhelming. In some cases, it seems to depend on the behavior of the bivalve, or its positioning in the sand or attachment to a substrate. I've been looking at a few studies today after reading your question. One study found that the oyster drill, Urosalpinx, had no preferencial site. Other studies seem to show a slight preference in a few other species. Personally, I haven't seen any preferences by Nucella on the the blue mussel, Mytilus. Bore holes can be anywhere on their shells. I have noticed that quite a few scallops have bore holes near their hinges, but I'm not certain which predator made these holes. I need to look into this. I often find signs of unsucessful predation, with holes that have been started but not finished.

These papers describe some very interesting research studies in great detail:

1. Gastropod predation patterns in Pliocene and Recent

pectinid bivalves from Antarctica and New Zealand

H. A. Jonkers

http://www.tandfonline.com/doi/pdf/10.1080/00288306.2000.9514884

2. Feeding habits of predatory gastropods in a tertiary (eocene) molluscan assemblage from the Paris Basin," John D. Taylor

http://palaeontology.palass-pubs.org/pdf/Vol%2013/Pages%20254-260.pdf

Abstract: The distinctive bore holes produced by two predatory gastropod superfamilies, the Muricacea and the Naticacea, can be recognized in their molluscan prey in a fossil assemblage from the Calcare Grossier (Eocene, Lutetian) from Dameray in the Paris Basin. Possible predators are six species of Naticacea and two of Muricacea. About 7000 mollusca representing 40 species were examined for boreholes of either type. ....

[Coco]

Hi,

Pagurus, if you have some specimens with labels, it isn't DAMERAY in Paris Basin (France), but DAMERY (without last "a"). It is east of Paris basin.

This post is very interesting. Here is another publication : http://www.app.pan.pl/archive/published/app48/app48-491.pdf

Coco

[Scylla]

Steve,

... but many holes will be caused by boring sponges. I've found quite a few fossil oysters (Exogyra, I think) from New Jersey with holes that look like they were made by sponges. Does anyone know if there are fossil sponges? Mike G

Yes there are many fossil sponges!Here

[Terry Dactyll]

Thanks for the paper links... I will have a read when I get chance...The bivalves position/orientation has a bearing on the hole which makes a lot of sense as this itself wont be consistently the same...

Just off topic slightly... Recently something came to light regarding ammonite predation in the UK, a small ammonite called a Promiceras found at Charmouth had crushing to the shell in consistently the same position on many prepped specimens roughly positioned at the end of the living chamber making it attacked from behind... The culprit squid/nautilus or even fish for that matter (Dapedium) knew where to bite and detach the critter from its home... I know Tarquin has a fossil nautilus beak and a Promiceras that was attacked this way in his collection...

Edited August 20, 2011 by Terry Dactyll

[steve p.]

Much of my time is looking at the sub 1mm to 10mm stuff. I am amazed when I see even sub 1mm snails with drill holes, and even on the oddly shaped scaphopoda. (As to what I see here in Texas eocene, seems that the Tusk shells (Dentalium) is more drilled than Horn shells (Cadulus), but that is an unscientific guess.)

[Pagurus]

Yes there are many fossil sponges!Here

HA! You guys do have fun, don't you. Thanks. I will definitely be researching fossil sponges. My background is in marine biology, so I have some familiarity with modern sponges, but I know very little about fossils. This forum is wonderful!