What are calcareous hard parts?

Some articles on calcareous hard parts:

Permian–Triassic Extinction Event - Extinction Patterns - Possible Explanations of These Patterns
... vulnerable marine organisms were those that produced calcareous hard parts (i.e ... Close relatives without calcareous hard parts suffered only minor losses, for example sea anemones, from which modern corals evolved ... Animals with high metabolic rates, well-developed respiratory systems, and non-calcareous hard parts had negligible losses—except for conodonts, in which 33% of genera died out ...

Famous quotes containing the words parts and/or hard:

    Though of erect nature, man is far above the plants. For man’s superior part, his head, is turned toward the superior part of the world, and his inferior part is turned toward the inferior world; and therefore he is perfectly disposed as to the general situation of his body. Plants have the superior part turned towards the lower world, since their roots correspond to the mouth, and their inferior parts towards the upper world.
    Thomas Aquinas (c. 1225–1274)

    It is a good lesson—though it may often be a hard one—for a man who has dreamed of literary fame, and of making for himself a rank among the world’s dignitaries by such means, to step aside out of the narrow circle in which his claims are recognized, and to find how utterly devoid of all significance, beyond that circle, is all that he achieves, and all he aims at.
    Nathaniel Hawthorne (1804–1864)