In Zoology
"Calcareous" is used as an adjectival term applied to anatomical structures which are made primarily of calcium carbonate, in animals such as gastropods, i.e., snails, specifically about such structures as the operculum, the clausilium, and the love dart.
The term also applies to the calcium carbonate tests of often more or less microscopic Foraminifera. Note that not all tests are calcareous; diatoms and radiolaria have siliceous tests.
The Molluscs are calcareous, as are Calcareous sponges are sponges (Porifera), that have spicules which are made of calcium carbonate.
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