Adjective:

1. (of lichens) having a thin crusty thallus that adheres closely to the surface on which it is growing;

   "crustose lichens"
   

crustn.外壳；坚硬的外壳；面包皮vt.盖以硬皮vi.结硬皮Crustal growth地壳生长crust breakers打壳机crust movement地壳运动Crust-drived壳源crusted tetter脓疱病crustosegments壳段crust fracture地壳断裂crustificationn.结壳；用覆盖物；镶嵌；硬壳crusta fibrosa[医] 牙骨质crusta petrosa白垩质