On the topic of eating non-sentient animals:
I eat them. I don't need to eat them: I am healthy without them, I can afford to choose what I eat and I have what I would call a very good knowledge of cooking and eating without animal products. Yet, I eat oysters or mussels every now and then (and to be honest, not as often as I’d like). I am also going to try sea urchins soon.
I call myself a Vegan, too. It’s a term that I find convenient and it describes how I eat fairly accurately. I understand and accept that voluntarily eating animals, even non-sentient ones, does not fit the definition of a vegan and is unusual. I would be comfortable saying that I am vegan + I also eat non-sentient animals. I eat them because I have not found a good reason not to and because I enjoy eating them. I would not consider myself an activist for “veganism”, I would however consider myself an activist against speciesism, for a fair consideration of the interests of all animals, for animalism (an all-encompassing word I like – similar to humanism except with “animal” instead of the restrictive “human”). As such, I try to think of the consequences of what I and others do on all animals, humans and non-humans and I care about them.
I invite you to read the three links I am providing after this post. I agree with them, but more importantly they provide plenty of information on why some (a few) of us vegans do indulge in eating mussels or oysters.
Everyone who has looked into it has concluded that it is unlikely to say the least that oysters and mussels could possibly be sentient. There is no proof that they are. We cannot say that they are sentient. I sincerely believe that they are non-sentient. They do not have eyes, they do not have a brain. They do not have a complex nervous system.
In addition and just as importantly, growing them and harvesting them is also ethical. They can easily be farmed and harvested without killing or harming or depriving one single sentient being. This in itself cannot be said of cereals where a lot of rodents are killed during the harvest. They are also “natural filters” and help their environment become cleaner. As such, they actually do require a reasonably clean environment if they are to be safe to eat. Oyster and mussel farmers must remain vigilant and concerned regarding the quality of their environment.
What’s more, and that’s just a lucky coincidence and a bonus, they are extremely rich in B12 and Omega 3 – the two things that happen to be the hardest to get without supplements or enriched food on a vegan diet.
I understand that most vegans and animal activists have no desire to start eating non-sentient animals or prefer not to eat them just in case. That’s cool. It’s sensible. For my part, I have no intention to eat them less often, let alone stop eating them as I see no reason not to.
In fact I enjoy showing and explaining that I eat them as I believe it is an open minded and pragmatic approach to veganism and because I believe it is beneficial for the environment.
To the argument that I should not or must not call myself a vegan or that I am a pescatarian because of this, I say that mussels, oysters, clams or sea urchins are not at all comparable to fishes. I would not kill or eat a fish or even a crab or a shrimp as they are sentient and they have an interest to live and not to suffer. I am no pescatarian. I am a vegan and I also eat oysters.
To the argument that it might make it harder for vegans to be served an actual vegan meal in the future because of people like me who call ourselves vegan and eat mussels, I say that I do not believe it is ever going to be the case. If anything, someone may ask “So would you also eat oysters and mussels like so and so?”. Many vegans drink wine, any wine regardless how it was refined. Do they also make it harder for all vegans worldwide who are worried they might be served non-vegan wine one day in the future?
I consider my reasoned and deliberate choice to eat non-sentient animals as part of my veganism, as part of the choices I make in my fight against speciesism and for animal equality. I accept that others find it unusual, perhaps even disturbing. I don’t accept being put down, excluded or insulted because of it.
http://www.animal-ethics.org/animal-sentience-why-should-it-concern-me/
http://www.slate.com/articles/life/food/2010/04/consider_the_oyster.html
http://sentientist.org/2013/05/20/the-ethical-case-for-eating-oysters-and-mussels/
http://sentientist.org/2013/06/15/oystersmusselspt2/#more-143 
