Help IDing Tridacna

Peter Clark · Jan 23, 2019

I took some photos while scuba diving in the Red Sea and am wondering about species. I am horrible at telling the difference between the various Tridacna species, especially after the fact from photos. Given the region these should be either Tridacna maxima or Tridacna squamosa. There are 4 different ones below. I am guessing 1, 3, and 4 are maxima since they are up on corals/rock. The 1st also appears to have smaller scutes too. The 3rd photo has a few in it, but I am guessing they are all the same type. The large one is blue which I think is more common in maxima. As for the 2nd one, I'm going to guess squamosa since it was on the sand. I have a video clip approaching the 2nd one if that is needed. Do these guesses sound right? I'm honestly basing this on a short amount of Google searching and digging through the forum. Whatever they are, I must say I love all Tridacna clams. I have a personal weakness for the blue maximas.

Thank you everyone!

reef lover · Jan 24, 2019

@DSC reef

DSC reef · Jan 24, 2019

#1- squamosa
#2- squamosa
#3- maxima
#4- squamosa
Thanks for sharing these awesome photos

Lovemyreef2015 · Jan 24, 2019

+1^^ cool pictures

Peter Clark · Jan 24, 2019

DSC reef said:
#1- squamosa
#2- squamosa
#3- maxima
#4- squamosa
Thanks for sharing these awesome photos

Thank you so much! Clearly I fail at IDing myself. I find it amusing that my scuba ID book for the area lists Squamosa as uncommon and yet 3 of the 4 I really focused on were that. I guess they are alone and stand out more? And so Squamosa can be found on rock/corals as well, and not mostly just on sand?

What features did you use to ID them? Did the pattern on the mantle help? Trying to learn.

Thank you!

DSC reef · Jan 24, 2019

To get an absolute ID, a full look at the shell would be required. I look at the mantle, the folds of the mantle and how they lay on the upper margin to see the spacing, the incurrent siphon tentacles, the eyes along the edge of the mantle as well. Tridacna can be confusing as the typical characteristics can be different in some clams. Some derasa can actually have scutes. I gave the best guesses I could in relevance to the pics so I could also be wrong. While squamosa are typically found on sand, they can attach byssal threads like any other clam. They are so beautiful in the wild. I really thank you for the pics.

shred5 · Jan 24, 2019

DSC reef said:
To get an absolute ID, a full look at the shell would be required. I look at the mantle, the folds of the mantle and how they lay on the upper margin to see the spacing, the incurrent siphon tentacles, the eyes along the edge of the mantle as well. Tridacna can be confusing as the typical characteristics can be different in some clams. Some derasa can actually have scutes. I gave the best guesses I could in relevance to the pics so I could also be wrong. While squamosa are typically found on sand, they can attach byssal threads like any other clam. They are so beautiful in the wild. I really thank you for the pics.

I believe sometimes their are hybrids out there.

Peter Clark · Jan 24, 2019

Wow I didn't even know those were eyes. Thank you!

DSC reef · Jan 24, 2019

shred5 said:
I believe sometimes their are hybrids out there.

I agree @shred5 but its yet to be proven.

DSC reef · Jan 24, 2019

Peter Clark said:
Wow I didn't even know those were eyes. Thank you!

Your welcome

Peter Clark · Jan 24, 2019

Just found another photo I overlooked. Squamosa? Both photos below are of the same clam in the middle of a small table coral.

Lovemyreef2015 · Jan 24, 2019

I also see two baby maxima's in the same picture as the blue maxima clam. Very cool pictures.

DSC reef · Jan 24, 2019

Definitely squamosa in the last picture. That's a wild picture, right in the middle of an acropora colony.

shred5 · Jan 24, 2019

Lovemyreef2015 said:
I also see two baby maxima's in the same picture as the blue maxima clam. Very cool pictures.

Yea I missed those two when I looked at it...

Good to see clams are making some comeback in the wild..

Peter Clark · Jan 24, 2019

shred5 said:
Yea I missed those two when I looked at it...

Good to see clams are making some comeback in the wild..

It was nice seeing clams pretty much everywhere. Every reef had them in the shallower areas. My trip covered a few places in the Gulf of Aqaba in the northern part of the Red Sea, and the photos above are from all the places. So both Israel and Egypt. I saw the same thing on my honeymoon in French Polynesia in 2013. That trip had been the first time I saw wild clams and the fact they were everywhere on almost every rock made me so extremely happy. I'm sure I must constantly puzzle other divers by focusing on little things they just swim right past. I don't want to even think about the amount of time I've played hide and go seek with small wrasses, especially the sixline wrasse. I only just got photos of one this last trip, and amazingly ended up with many photos including photo #5 above. Many years ago I spent even longer playing hide and go seek with a mantis shrimp in the Florida Keys...sadly I never got that photo.

shred5 · Jan 24, 2019

Peter Clark said:
It was nice seeing clams pretty much everywhere. Every reef had them in the shallower areas. My trip covered a few places in the Gulf of Aqaba in the northern part of the Red Sea, and the photos above are from all the places. So both Israel and Egypt. I saw the same thing on my honeymoon in French Polynesia in 2013. That trip had been the first time I saw wild clams and the fact they were everywhere on almost every rock made me so extremely happy. I'm sure I must constantly puzzle other divers by focusing on little things they just swim right past. I don't want to even think about the amount of time I've played hide and go seek with small wrasses, especially the sixline wrasse. I only just got photos of one this last trip, and amazingly ended up with many photos including photo #5 above. Many years ago I spent even longer playing hide and go seek with a mantis shrimp in the Florida Keys...sadly I never got that photo.

Oh nice I would love to dive the Redsea or French Polynesia..

I really want to go to Raja Ampat Indonesia too...
I have been watching allot of videos on that area on YouTube lately..
Have not been doing much Diving for a while now.
Anymore pictures I would be very interested to see them up here somewhere?

Peter Clark · Jan 24, 2019

shred5 said:
Oh nice I would love to dive the Redsea or French Polynesia..

I really want to go to Raja Ampat Indonesia too...
I have been watching allot of videos on that area on YouTube lately..
Have not been doing much Diving for a while now.
Anymore pictures I would be very interested to see them up here somewhere?

The Red Sea I got to do purely due to being invited to a wedding in Tel Aviv (they also held a ceremony I went to in Chicago) and that just made the perfect pretext to visit the region. Without that pretext I never would have gone I'm sure. I was sold on the whole trip the moment I thought about going to Jordan for Petra and then Eilat, Israel for diving, and then that grew into going into the Sinai in Egypt for even more diving and then over to Cairo to see the Pyramids. Probably won't ever make it back, but luckily I took thousands of photos (I never take a single photo of anything) and a lot of video. As for French Polynesia, I only dove once while there since my wife doesn't dive, but I wasn't overly impressed with it at the time. Oddly looking back at videos it looks far better than I remembered it. The weather wasn't perfect that week so that probably explains my impression.

I would LOVE to go to Raja Ampat. Indonedia, Philippines, Fiji, Australia, and Galapagos are all on my wish list. I'll be lucky to ever make it to a single one of those, but wow it would be amazing.

I send you a PM with a link to the best photos and video from diving on that trip.