280 days of Urbpandemonium #28
Who ever suspected that this empty cartridge, from Polaroid SX-70 film, would provide habitat for so many animals. I can see three species here--a single blue mussel, a number of tiny barnacles, but most prevalently a whole mess of slipper shells Crepidula fornicata.
Despite their flattened, uncoiled shells, these animals are snails. They don't glide around all the time like most other snails, instead remaining firmly attached to a substrate like a rock or another mollusk's shell or a piece of obsolete technology. Youngsters can crawl slowly, but after about 2 years of age they settle in, living the quiet life of a coastal suspension feeder.
Perhaps you have noticed the racy scientific name. Often you will encounter this shell stacked up on others of its kind. Most snails have both male and female sex organs, but slipper shells have a different strategy. "If the individual settles alone, it becomes male briefly, passing rapidly on to a female, especially if another animal settles on it to initiate chain formation. Sex change can only occur to the bottom-most male in a stack and takes approximately 60 days, during which the penis regresses and the pouches and glands of the female duct develop. If a juvenile settles on an established stack it develops and may remain as a male for an extended period (up to 6 years), apparently maintained by pheromones released by females lower in the stack (Fretter & Graham, 1981 in MarLIN, 2003)."