<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="220" name="crustaceans" parent="58" scope="Arthropods of class Crustacea, such as crabs, lobsters, shrimp, prawns, or barnacles, with hard shells (exoskeleton) and segmented bodies with pairs of jointed appendages."/><bt><term thcode="2" code="58" name="arthropods" parent="606" scope="Invertebrates belonging to the largest phylum of animals, Arthropoda, with an exoskeleton, segmented bodies, and jointed appendages, including many subphyla and classes, such as insects, crustaceans, horseshoe crabs, sea spiders, centipedes, millipedes, and the extinct trilobites."/><term thcode="2" code="606" name="invertebrates" parent="45" scope="Animals having no backbone or spinal column, such as insects, mollusks, crustaceans, worms, and similar organisms."/><term thcode="2" code="45" name="animals" parent="843" scope="Multi-celled organisms of the kingdom Animalia with eukaryotic cells (cells with distinct nuclei containing genetic material and bounded by thin membranes) that are heterotrophic (obtaining energy from organic substances produced by other organisms)."/><term thcode="2" code="843" name="organisms" parent="1174" scope="Living individuals that grow, reproduce, and die."/><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="848" name="ostracodes" parent="220" scope="Small aquatic crustaceans belonging to the subclass Ostracoda, characterized by a bivalve shell."/></nt><rt><term thcode="2" code="605" name="invertebrate zoology" parent="1339" scope="Branch of biology dealing with animals having no backbones or spinal columns."/><term thcode="2" code="1056" name="shellfish" parent="841" scope="Aquatic invertebrates with shells, usually mollusks and crustaceans. Includes clams, lobsters, and oysters."/></rt></descriptor>