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limestone

(Encyclopedia)limestone, sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making...

Hemichordata

(Encyclopedia)CE5 Dorsal view of an acorn worm, Saccoglossus, representative of the phylum Hemichordata Hemichordata hĕmĭkôrˌdāˈtə [key], small phylum of marine invertebrates closely related to both the ...

hermit crab

(Encyclopedia)hermit crab, a crustacean distinguished from true crabs by its long, soft, spirally coiled abdomen terminating in an asymmetrically hooked tail. Most hermit crabs protect this vulnerable portion of th...

hagfish

(Encyclopedia)hagfish, primitive, jawless marine fish of the family Myxinidae, of worldwide distribution in cold and temperate waters. Its rudimentary skeleton, of cartilage rather than bone, has a braincase, but n...

Ellsberg, Daniel

(Encyclopedia)Ellsberg, Daniel, 1931–2023, American political activist, b. Chicago, grad. Columbia Univ. (B.S., 1952, Ph.D., 1959). After serving in the U.S. Marine...

sculpin

(Encyclopedia)sculpin, common name for a member of the superfamily Cottoidea, bizarre fishes with large, spiny or armored heads and short, tapering bodies, found in both marine and freshwater habitats. The sculpins...

Regan, Donald Thomas

(Encyclopedia)Regan, Donald Thomas rēˈgən [key], 1918–2003, U.S. government official and financier, b. Cambridge, Mass. A graduate of Harvard (B.A. 1940), he went to work (1946) at a brokerage house that becam...

Porifera

(Encyclopedia)CE5 A. Canal systems of the three morphological types of sponges B. Internal anatomy of an asconoid sponge, representative of the phylum Porifera Porifera pōrĭfˈərə [key] [Lat.,=pore bearer],...

Comte, Auguste

(Encyclopedia)Comte, Auguste ōgüstˈ kôNt [key], 1798–1857, French philosopher, founder of the school of philosophy known as positivism, educated in Paris. From 1818 to 1824 he contributed to the publications ...

philosophy of science

(Encyclopedia)philosophy of science, branch of philosophy that emerged as an autonomous discipline in the 19th cent., especially through the work of Auguste Comte, J. S. Mill, and William Whewell. Several of the is...