Pen Shells

I have always called these shells sea fans or fan shells, but they are called pen shells. Pen shells are actually a type of clam and they live in soft and sandy mud.
This is usually about the time of year you find tons of these on the beach, but, so far, I'm only finding the normal amount.
However, in all the years that I have seen pen shells on the beach, I've never seen one closed with the clam still inside. The first picture is a typical pen shell picture with rough spines along the shell. The inside of this shell is creamy with a beautiful iridescent purple. The second picture is of an intact pen shell with clam visible inside(click on the picture to enlarge and you can see the clam easily.)
Pen shells have a tiny foot which sends out "threads" to wrap around buried shells and rocks. The threads, called byssus, are so strong that it is said they were used in woven garments for Roman Emperors.
When alive, the ponted end of the shell is down in the sand and the "fan" end extends into the water above the sand, making barefoot walking hazardous around a bed of these shells.
The shell is thin when the clam is alive and the shell is closed by flexing, unlike other bivalves.
Two small creatures live inside the shell - a crab ad a shrimp. these feed off the excess that the pen shell pumps inside.

Pen Shell

Pen Shell

Sunday Afternoon Beach Walk

We have had rain for the past 3 days, but today the clouds disappeared and we had a sunny, beautiful day. It was so warm at the house, I expected the beach to have a lot of walkers and joggers. But the wind at Isle of Palms was very chilly and strong and there were few people on the beach this afternoon.
Most of the starfish have been swept out in the ocean, just a few left for the birds to feast on. The sea gulls are plentiful, but sluggish and not in a hurry to get away from this human.
The beach was not as full of neat shells today, but I did find another sea urchin test and then found this dead sea urchin with spines still attached. ( To get a closer look, just click on the picture.)
Although a sea urchin is an invertibrate, they have developed "bones." inside the body, around the mouth, is a stucture called Aristotle's lantern. It provides attachments for muscles thaat move 5 shiny white teeth to scrape rocks, as they eat the algae from the rocks.
If this sea urchin were turned over, you would see a hole about half the size of the test and the teeth would be around that hole.
Pen shells are starting to show up on the beach. Last February they were all over the sand, just like the starfish in January. It will be fun to see if that occurs again.

Clams

As I've said, this must be the season for many shells of the same kind to wash on shore. There are piles of these clams - I've always called them Razor Clams, but they may be Jack-Knife Clams. They are almost transparent. Clams are bivalves with both a front and back shell which hinge together. They have a foot which sticks out between the two shells and is used for burrowing into the sand and/or mud and for scooting sideways. They have 2 tube-like siphons on the opposite end which protrude. The siphons go to the surface and take in water full of planktons to "eat" and oxygen for its gills which are located by the foot.
These clams prefer to stay beneath the sand or mud, but can be uncovered by rough surf where starfish, snails, and crabs encounter a feast.
This picture is not large enough for you to see all of the other shells in and around these clams, but there are baby whelks, cockles, and coquina along with other various and sundry shells.