Small triangular black shell

[yoavab]

Found that triangular black shell on a southern Israeli beach. the texture remindes me of a mud shell - brown and black on the outside and shining silver on the inside (the umbo is also shining silver). but the form is triangular somewhat like it belongs to Lasaeidae family. i was thinking it is Atrina vexillum but mine is much smaller and wider in proportions.

i would love to hear your thoughts and maybe help me identify this shell.