Patur—- ”’ The Gemara in Menachos (44a) describes the Chilazon:
1) It looks like the ocean
2) It’s form resembles a fish
3) It comes up once in 70 years
4) With its blood we dye the Techeiles
5) Therefore it is expensive
Let’s analyze the Murex Trunculus:
1) It does not look like the ocean
2) It does not resemble a fish
3) It does not come up once in 70 years(or have any known cycle of abundance)
4) The secretion used from the Murex Trunculus is no its blood
5)It is expensive, however Rashi explains that the statement of “Therefore it is expensive” refers back to the fact that it only comes up once in 70 years. The Murex Trunculus is expensive because you can only get around four drops of die per snail.
It seems that the Murex Trunculus is 0/5(according to the pashut pshat in the gemara. Obviously the Murex Trunculus proponents have a way to read each one of the criteria).”’
1.- What does look like the ocean mean to you? The Rambam is pretty clear it means the color. Now if you research this you will find out that in the water and the first few hours a after it comes out of the water, the shell is the color of the area it is taken from either blue or green.
2.Why not? have you ever seen a good picture of it? how about a picture of any other snail? which one looks like a fish and which one does not?
3. See the radvaz in chelek 2 in 685 that says nignaz means it stops coming up.
4. You were mechavein to tosfos in shabbos 75a dh ki. I will quote it for you ????? ?? ?”? ??? ????? ????? ?????? ????? ???? ??? ?????? ?? ???? ??? ???? ????? ???? ??? ?? ??? ????? ??? ??? ?? ?????? ??? ???? ??? ?? ???? ?????? ??????
5.Yet at the same time we know for a fact that it was caught using nets (see shabbos 74b)