Atlantic Kitten Paw
Plicatula gibbosa (Lamarck, 1801)
Family Plicatulidae
The Atlantic Kitten Paw, or "Kitten Paw" for short, is fairly common on S. Hutchinson Island beaches. Kitten Paws are small shells (.75") and come in a variety of colors with a different numbers of toes. Three toes being the fewest up to maybe a dozen toes in some shells. They attach to other shells and there's a flat area at the bottom on the paw where they have been attached.
Kittne Paw's (S. Hutchinson Island January 2021)
Some Eastern oyster shells closely resemble the "kitten paws" although they are not closely related physiologically (Kitten Paws are thicker and attach to other shells and are more closely related to scallop family) they often appear to be the same.
Eastern Oyster shells (S. Hutchinson Island Janurary 2021)
Harry Lee explains in an email January 2021: "There are fundamental differences in the soft anatomy and the hinge structure, among other characters, between the Eastern Oyster & Atlantic Kittenpaw.
The admitted similarities are superficial, not reflective of a true phylogenetic relationship. This phenomenon is called convergent evolution (synonym = homoplasy), e.g., bats, birds, and insects have wings.
Vernacular names, while often fanciful, make an attempt to show kinship, and each species, despite extreme variability in some characters has only one - at least officially (Turgeon, Quinn, et al., 1998)."
Additionally Eastern Oyster shells produce large foot-like shells which I have call "Duck feet" as well as shells that resemble boney human fingers. As explained by Dr. Lee the similarities are visual and they are very different shells.
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The Atlantic Kitten Paw
José H. Leal, Dec 2, 2016
The Atlantic Kitten Paw, Plicatula gibbosa Lamarck, 1801, is a bivalve commonly found on the beaches of Southwest Florida (and along the entire coast of the Sunshine State). Its vernacular name derives from the shell shape and, most likely, from its color pattern. It is not unusual for shellers to find complete shells (paired valves) of this inch-long species. Sometimes it is very difficult to separate the valves of a complete shell, not only because they are naturally very well adjusted to each other, but also because the shells may get cemented together by after-death incrustations and calcareous growth. The well-defined pleats give strength against crushing by predators, and also help prevent the shell valves from separating under stress. The species belongs in the Plicatulidae, a small bivalve family with only 16 species worldwide.