half naked pen shell atrina seminuda

No, you silly goose, this shell doesn’t have a bikini on… it’s really called a HALF-NAKED PEN SHELL! I found this rare PEN SHELL (Atrina seminuda) at Gulfside City Park on Sanibel Island, Florida a few weeks ago just after high west winds so there were thousands of shells that washed up on the beach. Talk about being silly… remember my crazy post “On The Beach With Shell Eggs And Ham, Pam-I-Am“? Well that’s when I found this very rare PEN SHELL. When I say “very rare” I mean it’s very rare for Southwest Florida. 

half-naked pen shell found on sanibel southwest florida

Okay wait….before you get bored with hearing about the not-so-attractive PEN SHELL, this is actually pretty dang cool, so go get some caffeine and stay with me, alright? And really, haven’t you seen tons of these shells if you’ve visited the west coast of Florida?

Last year when Shelling Sistah Susan H was here, she asked me if I had ever run into a third type of PEN SHELL  (the HALF NAKED) and told me to look at a picture of it online CLICK HERE. I studied the differences between this one and the STIFF PEN SHELL and the SAW TOOTH PEN SHELL. Okay, I’ve got it in my brain… if it’s here, I’m gonna find it. I searched for an entire year to find this stinkin thing! But I found it! I think I was just as excited when I found my JUNONIA… not.

I don’t think you will ever be collecting oodles of PEN SHELLS, (I’m not sure I know anybody who actually “collects” them) but it was sure exciting to me to finally find the darn thing. The only way to really tell it apart from the other PENS is to look at the inside muscle scar of the MOLLUSK… in other words- where the meat attached to the shell.

interior atrina pen shells southwest florida gulf

There is a slight variance on the outside of each of these shells. From left to right… STIFF PEN SHELL, HALF-NAKED PEN SHELL and SAW TOOTH PEN SHELL. I’m not really sure if you’ll be able to see the difference from this photo, but look very closely at the right side of each of the shells. That’s the hinge.. and it is very straight on the first and third shell but slightly curved on the middle one. So now that you know that the HALF-NAKED has a curved hinge, go back to the last photo with all 3 shells and see the big gap in-between the valves of the middle shell. That’s why I even picked up the shell in the first place, I saw that slight curved hinge and immediately thought to myself… OMG maybe that’s it!

atrina pen shell differences

Maybe this is a better view of the curve in the hinge… on the left is the HALF-NAKED and on the right is the STIFF PEN SHELL. Can you see it now?

the difference in pen shells

This is the real giveaway on the difference between these shells. The middle one is the HALF-NAKED (isn’t that just the funniest name? I get so tickled every time I say it!). Can you see more lines and shapes on the HALF NAKED right in the middle of the shell?

interior valve atrina pen shells seminuda difference

The next photo is a close-up of that shell and it almost looks like a face, right? Do you see the “eyes”? Okay, that is the muscle scar. Right above the “eyes” is a wide milky space before it changes complete color (like a hair line). The whole milky or pearly area is called the nacreous. The HALF-NAKED is the only one of our PENS that the muscle scar leaves such a prominent space below the nacreous border.

atrina seminuda muscle scar and nacreous

This next one is the STIFF PEN SHELL… the most common PEN SHELL on our beaches and it looks almost identical to the HALF- NAKED. I’m sure you’ve all seen this one if you’ve walked on the beaches in Sanibel or Captiva and you’ve probably cussed at it after you stepped on it, right? Ouch!

stiff pen shell atria rigida

Here’s the interior of the STIFF PEN. It’s hard to see the muscle scar on this one but there is definitely no obvious space between the top of the muscle scar and the border of the pearly part.

stiff pen shell atria rigida nacreous

This next one is the SAWTOOTH PEN SHELL. This one is easy to tell the difference from the others since it is much lighter in color and it has much smaller spines that don’t stick out (to cut your foot). I didn’t do a close up of the interior nacreous area because it didn’t really show up well… and …. wait! wake up! I’m just getting to the good part so gulp more caffeine, would ya? LOL

saw tooth pen shell atria serrata

This is how I found my first HALF-NAKED PEN laying on the beach at Gulfside City Park.

half naked pen shell at gulfisde city park

I took the shell to Dr. Jose Leal at the Bailey-Matthews Shell Museum to get a positive ID from him. He positively identified it for me as the Atrina seminuda (HALF NAKED) and then told me that they did not have one of these shells at the museum. Since it was my first one I’ve ever found, I told him he could borrow it to photograph it.  I know, I know, it sounds stingy that I didn’t donate it to him but geeeeez, remember…. Ive been looking for this guy for a year!

The first one I took to him to get a positive ID wasn’t so pretty and it cracked a little when I opened it up to look at the muscle scar…

sanibel atria seminuda pen shell

So I went hunting again and low and behold… I found two more after looking at thousands of them all along Sanibel. Gulfside City Park was the winner again. I found a perfect one with no cracks that I’ve shown in my photos here and I donated this one to The Bailey-Matthews Shell Museum…

half naked pen shell atrina seminuda

They will soon have it on their website as a Southwest Florida shell and have my shell in the photo. And yes, it’s still the only one they have so far- Dr Leal looked in the archives and couldn’t find another one. I’m so proud of that little PEN SHELL! Hahaha- Really, Who would have thought I’d ever be so happy about a PEN SHELL. heehee. And I would never have known to look for it if it hadn’t been for sweet Susan H! Thank you Susan H for asking me about it and giving me something to hunt for. I always love to find new things on the beach!

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