not sure what kind this is but i've had it for a couple of years. got it when it was about 2". it is now about 7".
<a href="http://s6.photobucket.com/user/Ninapearl/media/TANK%202015/clam_zps1cxjlu7t.jpg.html" target="_blank"><img src="http://i6.photobucket.com/albums/y203/Ninapearl/TANK%202015/clam_zps1cxjlu7t.jpg" border="0" alt=" photo clam_zps1cxjlu7t.jpg"/></a>
fts
<a href="http://s6.photobucket.com/user/Ninapearl/media/TANK%202015/fts_zpsfpcjlqwm.jpg.html" target="_blank"><img src="http://i6.photobucket.com/albums/y203/Ninapearl/TANK%202015/fts_zpsfpcjlqwm.jpg" border="0" alt=" photo fts_zpsfpcjlqwm.jpg"/></a>

<a href="http://s6.photobucket.com/user/Ninapearl/media/TANK%202015/clam_zps1cxjlu7t.jpg.html" target="_blank"><img src="http://i6.photobucket.com/albums/y203/Ninapearl/TANK%202015/clam_zps1cxjlu7t.jpg" border="0" alt=" photo clam_zps1cxjlu7t.jpg"/></a>
fts
<a href="http://s6.photobucket.com/user/Ninapearl/media/TANK%202015/fts_zpsfpcjlqwm.jpg.html" target="_blank"><img src="http://i6.photobucket.com/albums/y203/Ninapearl/TANK%202015/fts_zpsfpcjlqwm.jpg" border="0" alt=" photo fts_zpsfpcjlqwm.jpg"/></a>