<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="605" name="invertebrate zoology" parent="1339" scope="Branch of biology dealing with animals having no backbones or spinal columns."/><bt><term thcode="2" code="1339" name="zoology" parent="650" scope="Branch of biology that deals with the reproduction, development and growth, anatomy, physiology, and behavior of animals."/><term thcode="2" code="650" name="life sciences" parent="1019" scope="Branches of science that study living and fossil organisms."/><term thcode="2" code="1019" name="sciences" parent="1" scope="Major educational fields, fields of study, and professional groupings within USGS."/><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="341" name="entomology" parent="605" scope="Branch of zoology involved in studying insects."/></nt><rt><term thcode="2" code="55" name="arachnids" parent="58" scope="Carnivorous arthropods, chiefly terrestrial, of the class Arachnida including spiders, scorpions, mites, ticks, false scorpions, palpigrades, solifugids, and harvestmen."/><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="130" name="bryozoans and brachiopods" parent="606" scope="Aquatic invertebrates, usually marine, belonging to the phyla Bryozoa and Brachiopoda.  Brachiopods, or clam shells, are solitary living invertebrates characterized by two shells and a lophophore, which is a complex food gathering organ.  Bryozoans are colonial and include moss coral and moss polyps."/><term thcode="2" code="177" name="coelenterates" parent="606" scope="Freshwater and marine invertebrates, such as corals, jellyfish, and sea anemones, belonging to the phylum Coelenterata and living as sedentary polyps or free swimming medusae."/><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."/><term thcode="2" code="305" name="echinoderms" parent="606" scope="Marine invertebrates of the phylum Echinodermata with a radial body and a calcareous exoskeleton. Includes starfishes, brittle stars, sea lilies, sea urchins, and sea cucumbers."/><term thcode="2" code="395" name="flatworms" parent="1336" scope="Soft flat worms of the phylum Platyhelminthes, which are often parasitic. Includes tapeworms and flukes."/><term thcode="2" code="543" name="horseshoe crabs" parent="58" scope="Marine arthropods, usually classed as Merostomata, which have a broad crescent (horseshoe-shaped) cephalothorax."/><term thcode="2" code="604" name="invertebrate paleontology" parent="861" scope="Branch of paleontology which deals with fossil animals without backbones."/><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="757" name="mollusks" parent="606" scope="Invertebrates belonging to the phylum Mollusca with soft, nonsegmented bodies, often covered by a hard shell.  Includes snails, clams, oysters, whelks, mussels, slugs, octopuses, and squids."/><term thcode="2" code="848" name="ostracodes" parent="220" scope="Small aquatic crustaceans belonging to the subclass Ostracoda, characterized by a bivalve shell."/><term thcode="2" code="1006" name="roundworms" parent="1336" scope="Worms of the phylum Nematoda, often parasitic, such as hookworms and pinworms, having soft cylindrical bodies without segments."/><term thcode="2" code="1038" name="segmented worms" parent="1336" scope="Worms belonging to the phylum Annelida, with soft bodies divided into segments and distinct heads. Includes leeches, earthworms, and marine worms."/><term thcode="2" code="1056" name="shellfish" parent="841" scope="Aquatic invertebrates with shells, usually mollusks and crustaceans. Includes clams, lobsters, and oysters."/><term thcode="2" code="1094" name="sponges" parent="606" scope="Aquatic invertebrates belonging to the phylum Porifera having internal skeletons of silica or collagen, porous body around a cavity or cavities, and usually living in stationary communities."/><term thcode="2" code="1336" name="worms" parent="606" scope="Invertebrate animals of the phyla Annelida, Nematoda, Memertea, or Plathyhelminthes, that have long thin rounded or flat bodies without obvious appendages."/></rt></descriptor>