First we started by examining the tide pools at the western side of the island where we encountered several creatures such as Mussels, Periwinkles, Razor Clams, Lobsters, Crabs and Tunicates, some of these we’ve already encountered at the docks under The Barking Crab. There was an abundance of creatures all around us, all we needed to do was just look down and see a few hermit crabs walking around several periwinkles, mussels, clams and shore crabs waddling around everything as well.
We saw two different types of aquatic snails at the beach, the Common Slipper Snail (Crepidula fornicata) and the Common Periwinkle (Littorina irrorata)1 while the Common Periwinkle looks similar to the Rough Periwinkle and Checkered Periwinkle, those two species have a horned operculum (the lid of the shell) while the Common Periwinkle has a smooth and thin operculum. We also examined some shells with a small hole drilled into them, this fits the predation method of Moon snails, which are likely candidates. However since we didn’t actually spot any, it could be another species that predates in the same manner but I observed none.
Moon snails (and other snails) eat by attaching themselves to other shells, drilling a small hole using their radula and injecting digestive fluid inside the shell, then they suck back the partially digested mollusk inside.2
I’ll have to adopt the predation methods of gulls for my hypothesis of how the broken Grove Snail shells got near the beach. Seagulls (or possibly another bird) pick up snail shells take them to the rocky beach and drop them on a rock in order to crack them open which gives them access to the snail inside the shell.2
We also saw Grove Snails, but I’m not sure whether they were White Lipped (Cepaea hortensis) or Brown Lipped (Cepaea nemoralis). The color variations between the shells we saw are random variations that are similar between the two species, with the difference between the two can be identified upon examining the lip of their shell, the one I examined closely and photographed seemed to be a White Lipped but genetic variation in the Brown Lipped can allow a white lip and vica versa. this cannot be determined without dissection.3
I’m not sure about the exact connection between the marine snails and the land snails, if we examine the taxonomy they are both different family, which implies very little genetic connection, however, somewhere down they line they had a common ancestor which eventually evolved into these two species. The majority of snail species are marine, which suggests a longer history for this form, that evolved into air breathing land variety.
We saw some similar species in the two different environments, such as the Asian Shore Crab, Mussels and Orange Sheath Tunicates which attach themselves to where they can. We didn’t witness any snails as those are (I assume, mostly) grounded, and it was difficult to find crabs as well. There are several differences between the habitats: The tides are vertical at the harbor compared to the ocean, there’s less current in the harbor, human interference is much more common which shifts wild life from place to place. It’s hard to saw without properly examining more of the harbor, such as the bottom of the ocean, as there isn’t really a coastline.
Again, you can find my pictures from our day at: