Wildlife Spotting

I have not idea what this is, or even what category to put it in. I found these 3 about a foot off the shore line on the Aegean Coast of Turkey. I assume the large one was dead, as the two smaller ones seem to have been anchored in the sand where as this one just seemed to be laying on the sand, the only movement coming from it was due to the gentle tidal movement. I did not see any more of these along this stretch of coastline.