Tuesday, August 5, 2008

Periwinkles and Land Snails

Erald Pelari

Date: August 4, 2008

Location: Lovells Island

Weather: Hot and Sunny

Temperature: High 70’s and low 80’s

Species: Periwinkles and Land Snails

Today we took a trip to Lovells Island near Boston Harbor and we observed and took data on Periwinkles and Land Snails. After we got off the taxi boat we walked across to the North East corner of the Island where there is a large tide pool. While walking around the islands shore line we stopped and decided to flip some rocks and see if there were any crabs lying underneath them. I myself had to turn three rocks until I found one where there were two crabs lying underneath. They had green color, were about 2 inches wide and 3 in long. They had very small claws probably around 1.5 inches and their legs were of similar length as well. I believe that these were Green Rock Crabs. We arrived at the island around 10 AM and started our data gathering and observation at around 10:30 AM. Luckily for us the water had receded enough due to a low tide and we could walk into the water about 20-30 ft off the shore and gather periwinkles. After the periwinkles we were separated into groups and looked for live land snails and shells of dead snails. We were supposed to collect at least 10 shells per group.

Observed Periwinkles at the tidal pool, took measurements of height, measured the opening of the shell where the mouth is. I also observed the color of the periwinkles and the shape of their shells. We were also looking to see how they moved around when placed on a rock outside the water. Then we moved into gathering land snails. Here we were looking for shell color and the body color of the snail, texture, and other things.

For this trip I decided to bring with me more tools that would help me investigate the species a lot better then what I brought with me the first day of observations.
Digital Camera- used to take pictures of the periwinkles and land snails as well as film the movement of periwinkles
Ruler- used to measure the length, height and width of the various periwinkles
Magnifying Glass- to take a closer look at the shells and opening/mouth of the periwinkles and at the complete texture of the land snail’s body
Notebook- to keep notes and records of the data and observations
Pen- used primarily for writing but also for poking the periwinkles and the snails and observing their reaction.
Guide Book- used to help in identifying any species that I saw and did not know the name of for example: The Green Rock Crab.

Observation and Data:

Smooth Periwinkle
What is a periwinkle?
According to Peterson’s Field Guide book the periwinkles come form the shelled Gastropods Family. It has a spire, a body whorl and a suture and an operculum. It is the most common northern rock and wharf piling winkle. There are common, smooth, rough and Gulf periwinkles.

Data and Observation:
The first periwinkle that I pulled out of the water was small and had a blackish color. It had a height of 2.5 cm and an opening of 1.2 cm in diameter. The shell had a few cracks on top indicating that the periwinkle must be mature. The opening of the mouth is of brown color and if poked with a pen will retract into the shell to seek protection. All the periwinkles that I saw and captured were sort of glued to smooth rocks. I also grabbed some periwinkles that were smaller in size. Their height was about 1.5 cm and the opening of the shell was about .7mm long. Looking at them closely one could see even with the magnifying glass that their shells had no cracks, meaning that they must be young periwinkles.

I believe that these are smooth periwinkles because they look similar to the ones shown on Plate 20 in the Guide book. Also if you look at the picture posted above you will see that at after their shell dried it does resemble a smooth surface seeing by the human eye. I also came to this conclusion after I read the article by the young naturalist Emily who dictated that Common Periwinkles are found in the coast of Maine and if you look at the pictures you will see that they have a smooth shell and it resembles the shape of a small moon shell. One thing that I can not prove is weather or not they had an umbilicus because I did not look for it. But if a periwinkle is smooth then it can not have an umbilicus.

Land Snails

Land snails come in two verities Brown-lipped snails and White-lipped snails. One can distinguish what sort of a snail it is by looking at the opening of the shell where the snail comes out also called the “lip” and see whether that part of the shell has brown a brown ribbon circling it or a white strip. The first snail that I saw and grabbed for more observations was stuck behind a leaf. I guess snails love to stay on the back of the leaves to avoid being seen by predators but also the fact that the back of a leaf might be a little softer then the top part (my opinion), making it easier for the snail to bite. This snail had brown color with a white ribbon around it. The snail’s superior and inferior tentacles were both out of the shell and extended as well as its back end “the tail”. This was a white-lipped snail.

We ended up gathering a few live snails and a lot of shells from dead snails. The live ones were primarily white lipped, but we did have some brown lipped snails as well. They were very active and would move around the container and eat the leaves. The shells form dead snails came in various colors. Some yellow, some brown, some dark brown, and some had different colored ribbons and various numbers of ribbons. Out of all these shells that we had gathered only one shell was plain white. This would lead me to believe that a yellow shell is not the best color for protection where you are surrounded by green leaves and brown tree branches. But that must also be that the area that we were looking at did not have many yellow shelled snails. We also designated one tem member to collaborate with other team members to try and sort the shells. One system was to divide them by color and the number of ribbons. Others decided to separate them depending on background color. One thing we did not do and should have done was to try and sort the shells based on white and brown lipped.

Periwinkles vs. Land Snails

Periwinkles have strong shells whereas Land Snails have softer shells. Land Snails have a superior and inferior tentacles whereas periwinkles do not have tentacles. When periwinkle moves they do not show their head and the tail end as does a land snail (Please see the video posted by Kris Pandeli on his blog). Periwinkles have a pointy shell and land snails have a more round one.

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