When walking the local beaches, National Shell Museum staff and local enthusiasts are always on the lookout for shells that are distorted, clipped, or bored by predators, shells with attached creatures, and any other molluscan oddities that may catch their fancy. A couple of weeks ago, Dr. Mike Reardon, who volunteers in the Museum collection, picked up a large fragment of a Sawtooth Pen Shell with several dead, dry mollusks attached (see photo). Among those were barnacles, Black-foot Slipper Snails (the ones with white shells, blue arrows), and young Eastern Oysters known as “spat” in the oyster trade (mostly the ones with brown rays on a white background, red arrows).
Mike and I were noting how similar the shell shapes were between the slipper snails and the juvenile oysters, and the possible benefits for these mollusks to have these slim, almost flat shapes. The slipper snails are gastropods, and the young oysters are bivalves, yet both species can take advantage of the very low-lying, level profiles. These low profiles probably make it more difficult for predators to remove the mollusks from the shell or rock where they grow, and, in some cases, allows them to grow inside the shell aperture (the opening) of a larger living snail (such as a Lightning Whelk) without much hassle to that host mollusk.