These are clovisses, or Tapes decussatus. In French T. decussatus is "clovisse" and T. decussatus form fusca "palourde", or Manila Clam, Japonaise, Alemeja. The local name in Siargao is punau.
They're delicious, so here's a simple, and very good recipe, thanks to Sophie:
24 clovisses or palourdes
(steam for a moment or so to open them)
125 g butter
25 g shallot
5 g garlic
10 g parsley
10 g almond powder
This recipe is rather easy to do! Put the full halves of the palourdes on a dish. Mince parsley, garlic and shallot separately. Put Shallots with a little part of the butter in a small pan, and heat gently until the shallots are transparent. Add parsley, garlic and all the butter. Heat till the butter is foamy. Then add it on each palourde and dust them with the almond powder. Put the dish in a hot oven for 5 minutes, not more and eat immediately !
These shellfish normally grow in lagoons, or other very quiet waters. They are lazy, and don't like to be disturbed by currents and weather
The recipe give by Sophie is not very sophisticated, (it is after all, French) but you could do a lot more with these shellfish, See other posts about how shellfish can be made into divine meat.