Strange Slippers on A Beach

​Sometimes you can find some weird looking stuff on the edge of a sandy beach around New York Harbor.
 
Recently while enjoying a beach walk on an unusually warm February afternoon, I came across a cluster of slipper shells, also known as boat shells, attached to each other. To people who are unfamiliar with local shellfish, I would have to image this would be a rather bizarre discovery.
 
But the oddness does not stop with just their looks. Slipper shells are actually aquatic snails or gastropods that produce cup-like shells as exo-skeletons, which some people have characterized as slippers or boats. These snails are one of a few marine snails that do not produce coiled or spiral shape shells, such as whelks or moon snails. Slipper shells are strange snails indeed. 
 
This little gastropod usually attaches itself with its large foot to hard objects, such as to rocks, piers, jetties, horseshoe crabs, or even to other slipper shells. But these snails are not parasites; they don’t feed off their hosts. Instead, slipper shells are filter feeders that feed on plankton from the sea, more like bivalves. They will use cilia to create water currents that flow phytoplankton and algae into their mouth.
 
Slipper shells often stack up on-top of each other for convenient reproduction. The snails are hermaphroditic. During the spawning season, younger snails are males. Later in life, those males will become female to prevent self-fertilization. Once they change into females, they remain females.
 
When you find a cluster of slipper shells, in general, the larger females are on the bottom, the smaller males are on the top, and the hermaphrodites are between the two. If the ratio of males to females gets too high, the male reproductive organs will decrease and the little snail will become female.

Some people find the meat inside slipper shells to be quite delicious.  Like their gastropod cousins Limpets and Abalone, slipper shells are edible with a slightly chewy consistency.
 
Authors Morris K. Jacobson and William K. Emerson in their classic book, Shells of the New York City Area, published in 1961, wrote that slipper shells “inhabitant primarily quieter bays and inland waters where it appears in astounding numbers….It is far more common in Coney Island than in Rockaway, thus showing that it does not prefer the outer beaches.”
 
Today, slipper shells are quite common and can be found in large numbers throughout New York Harbor, especially in shallow water areas of less than 20 feet. They seem pollution tolerant, especially of harmful algae blooms, which does them well living in the tough, turbid waters of New York Harbor.