Giant clam ID, feeding and nutrition, and Pyramidellid snail removal

skinz78 · Mar 14, 2011

Giant clam Identification.

Clam ID can be quite confusing at times and I myself occasionally see one that gets me wondering. The best way to ID giant clams is to look at the shells. Most importantly the bottom of the shell and the byssal opening.

For instance lets look at the T. crocea, it has the largest opening of any of the giant clams and it is also the smallest clam so it is easy to tell. The opening usually resembles a large teardrop. They are the smallest of the giant clams so the teardrop byssal opening is really pronounced.

The sides of the T. crocea's shell is more symmetrical (short front to back, high bottom to top). The T.crocea shell can close completely and is relatively smooth, sometimes with scutes at the top edge of the shell. Max size about 6 inches. I have seen T. crocea with scutes all the way up the shell, this is more common in farmed T. crocea and some vendors may have tried to pass them off as T. maxea because of the scutes. They top out at a max size of about 6 inches.

T.crocea with scutes all the way up the shell.

For me it is pretty easy to tell a T. crocea by looking at the mantle, most of them are fairly close in resemblance to this one. Seems we get a lot of blue T. crocea imported to us.

Next we have the T. maxima, they are the second smallest of the giant clams.
They have a large byssal opening, but narrower and smaller than T. crocea in comparison to the over all size of the shell.

Also the shell is more elongated from front to back and is shorter top to bottom, with pronounced scutes in tight rows all the way down to the base of the shell. They top out at a max size of about 18 inches.

With the T. maxima's mantle being one of the most colorful to ID just from viewing them top down. They often have quite crazy patterns and this makes it hard.

skinz78 · Mar 14, 2011

Next in size is the T. squamosa clam, also known as the ruffled clam due to the large size of the scutes on the shell. T. squamosa also has a teardrop byssal opening when younger but as it gets bigger the opening closes with shell growth.

This T. squamosa was about 4.5" at the time of the pic.

T. squamosa's shell is symmetrical with length almost the same as height. Very large, widely spaced scutes all the way down to the base. Maximum size tops out at about 18 inches.

T. squamosa is often confused with T. maxima when trying to ID from the mantle. Their color variation is very similar although T. squamosa is more commonly seen in gold, purple, green or brown and very very rare to see a blue one. They also have quite a pronounced fringe around the incurrent siphon. Other clams have this but not nearly as pronounced as the T. squamosa. They top out at a max size of about 20 inches.

T. derasa has a very narrow byssal opening that closes with age. When smaller the T. derasa shell is very narrow but gets much wider as it ages and eventually they won't be able to fully close.

T. derasa has a smooth, symmetrical shell with 6 or 7 vertical folds (this is the main distinction between Derasa and Gigas). They can develop scutes but most often they get broken off really easily. They top out at a max size of about 30 inches.

They are fairly hard to ID by looking at the mantle but often they have grain of rice shaped florescent stripes. They also have a fringe around the incurrent siphon and this sets them apart from T. gigas.

T. gigas has a narrow byssal opening that closes with age. Smooth symmetrical shell with 4 or 5 prominent vertical folds. They are the largest of the Tridacnid clams getting over 48 inches in length.

These pic's are old, I had one that I grew from 1.5" to 6" in a year. The growth rate scared me so I sold it.

In this pic it was about 2" and it had actually attached to my Fighting conch. It was quite funny when I noticed my clam kinda hopping across the tank behind the snail.

I didn't get many pic's of it and most aren't that good at all. This is the clam top down when it was about 2.5"

Here it was at 6" right before I sold it.

Last of all there is the Hippopus Hippopus, they are available to us but not many people keep them.

H. Hippopus is the easiest to tell apart of all the giant clams, the shell shape is completely different and closely resembles a horse's hoof. They have a very narrow byssal opening that's flattened and squared off.

H. hippopus has somewhat rough shell that may have nodules. The mantle does not hang over the edge of the shell. They top out at a max size of about 25 inches.

Here is a frontal shot of a H. hippopus clam's mantle, they can have electric looking lines in them and usually have a cammo look to them.

skinz78 · Mar 14, 2011

Tridacnid feeding and nutrition.

Tridacnid or more commonly know as giant clams fulfill their nutritional requirements mainly by:

1. Filter feeding

2. Absorbing dissolved organic compounds "mostly ammonia" from the water.

3. The giant clams mainly create their own food by using zooxanthellae in a symbiotic relationship to manufacture food for themselves.

Tridacnid clams obtain their zooxanthellae when they are juveniles when the zooxanthellae is introduced through the feeding organs and move from the stomach to the mantle through the Zooxanthellal Tubular System or "ZTS". The zooxanthellae are resistant to digestion, and this is how the algae safely makes it to the mantle. The "ZTS" tubules extend from the stomach into the mantle tissue, making clams different from corals who's zooxanthellae are located within individual cells. The zooxanthellae (through photosynthesis) provide clams with the same products corals receive.

The zooxanthellae provides nutrition for the clam when it transforms carbon dioxide and dissolved nitrogen, such as ammonium, into carbohydrates and other nutrients for their hosts. Some other nutrients the clams receive from the zooxanthellae are: carbon (in the form of glucose) and amino acids like alanine. The zooxanthellae uses the nitrogenous wastes of the clam (mostly ammonia) as a nitrogen source. The Tridacna clams benefit greatly from this system because it allows them to use a very efficient internal food source.Sometimes you will see giant clams with a long hair like strand coming from the exhalent siphon, this is usually excess zooxanthellae that the clam is releasing.

The Tridacnid mantle absorbs dissolved nutrients directly from seawater. When exposed to light, the zooxanthellae in the mantle will take in ammonia, nitrate, phosphate and sulfate from the water and use them to make amino acids. This explains why Tridacna clams can be able to lower these substances within our home aquariums. Although they can do this it is my opinion that it would take a large number of clams in a small system to see any difference in these levels.

The role of phytoplankton in Tridacna clam nutrition is not understood. Although it is believed that phytoplankton provides the clam with some protein, it may be just a carbohydrate source.

skinz78 · Mar 14, 2011

Removal of Pyramidellida snails

Pyramid snails are tiny little terrors who have the ability to reproduce very quickly and their strength comes in numbers. It doesn't take long for a bunch of these little parasitic snails to completely decimate a clam. There are thousands of different species of Pyramid snails so positive ID is nearly impossible, some of them only attack clams and some attack other snails, I have had both types. It is also thought that some have the ability to paralyze a clam with toxic saliva to make it easier on themselves. They kill the clams by using a trunk like proboscis to penetrate the clams mantle and suck the body fluids out.

A pic of an adult Pyramid snail next to a toothbrush for size comparison.

What you will need to remove these snails from clams, a toothbrush, rigid pointy object I use a pocket knife, but I have used shish kabob skewers in the past, and a tub of water for rinsing. Some people add certain Wrasses to the display tank to help with removing Pyram snails. The problem is that the snails are nocturnal and the Wrasses are diurnal. But IMHO it couldn't hurt to add the Wrasse just in case he snag's a few of them here and there.

These snails will be more active when the lights are out so when you do manual removal it is best to do it one hour after the lights turn off.

What you will be looking for is tiny, rice grain sized snails near the opening's of the clam. Mainly the snails will be just under the mantle on the shell. This is also where they usually lay their eggs. IMHO the egg masses are just as or if not more important to remove from the clam than the snails themselves. The eggs will be in clear masses usually as close to the mantle as possible. It is hard to see in this pic but they are the jelly like substance just above my horrible blue arrows.

What I do is take the toothbrush and thoroughly scrub the clam and rinse it repeatedly in the process. Although scrubbing removes a lot of the snails you can't get them all by doing so, there will be snails deep in the folds of the clams scutes and that is where the knife or shish kabob skewer comes in handy. I dig them out and if there are scutes that are grown too closely together to get into I break the scutes out to gain access because 9 out of 10 times there will be snails in there. Breaking the scutes doesn't harm the clam and it won't feel a thing. Here is a pic of a snail that the toothbrush didn't get.

Last but not least you will need to check the bottom of the clam near the byssal opening. The snails usually congregate there during the day.

Clean Pyram snails off of clams is a long process, you will need to clean them every other night for at least a month. Even if you don't see any snails on nights still keep checking them till you are 100 percent sure they are all gone. Another thing that I do is place a Tupperware container under the clam with a little bit of sand in it. Every time I clean the clam I throw away the sand in the container and replace it with new sand. The snails will burrow down into the sand to hide during the day.

Korpi · Mar 27, 2011

great info, thanks

skinz78 · Mar 27, 2011

No problem, if you have any questions feel free to ask!

swannyson7 · Mar 27, 2011

Awesome write up skinz! Thanks for the info

Paul_N · Mar 27, 2011

Definitely a must read for us clam junkies! I always pick mine up and check them out periodically(mine are in sand/crushed coral and not attached to rock). I have never had a ps so my yellow wrasse must be doing his job. I also have purchased all my clams off of reefers that had them for a while and were getting rid of them, so I'm sure that makes a difference. When the time comes for me to get my blue dot squammy I'm sure I will have to get it retail.