KGS Home Page Education Index Page Start of this Report

Ancient Life in Kansas Rocks, part 26 of 27


Please use the "Back" command of your browser to return to the page you were viewing. These terms are defined in the sense they are used in this book. In some cases the definitions are linked back to specific sample pages.

Accessory cusps. Small raised portions of a tooth in addition to the central raised principal cusp. See sharks.

Adductor muscle. A muscle that serves to close the valves of a brachiopod or clam and which commonly leaves a muscle scar.

Ambulacral groove. One of the five grooves arranged as a star, found in starfish, echinoids, crinoids, and related animals, and which leads to the mouth, serving as a passage down for food.

Amoeboid. Like the simple animal Amoeba, consisting of one cell.

Anal sac. An upward protrusion of the tegmen, on which is located the anal opening through which body wastes are passed. See crinoids.

Anterior. The front.

Apex. The highest point of a cone-shaped snail shell. See snails.

Appendage. A limb such as an arm.

Aquatic. Living in water.

Arms. The appendages of a crinoid that extend upward and outward from the body. See crinoids.

Articulated. Held together by joints, as a human arm, or hinged as a door so that the parts may move.

Auricle. The ear-like extension of the hinge found on some clams. See clams.

Axillary. A plate on a crinoid arm above which the arm branches into two series of plates. See crinoids.

Biconvex. When each valve of a brachiopod or clam is rounded outward like the outside of a ball.

Bilaterial symmetry. Divided into two halves that appear to be mirror images of each other by an imaginary plane passing between them. See symmetry figure.

Bivalve. Having two shells or valves, as in brachiopods and clams.

Brachial plate. One of the kinds of crinoid arm plates. See crinoids.

Brachial valve. The brachiopod valve that bears the lophophore; the dosal valve. See symmetry figure.

Brachidium. The skeletal part of some brachial valves that supports the lophophore.

Brachiopod. A marine invertebrate that utilizes a lophophore for food gathering, and has two differently shaped valves and equilateral symmetry. See brachiopods.

Brackish. Water that is more salty than fresh water, but less salty than normal ocean water, common in estuaries and marshes where freshwater mixes with sea water.

Byssal threads. Thread-like fibers secreted by a clam which extend outward from within the shell through a notch and fasten to some object on the sea bottom.

Calcareous. Contains calcium carbonate.

Calcium carbonate. (CaCo3) A principal component of limestone which, when burned, yields lime.

Cartilage. An elastic tissue in animals and fishes that commonly becomes bone in the adult vertebrates, although in some (such as sharks) it does not.

Cell. The smallest, usually microscopic, unit of living matter that is capable of living as an independent unit and performing all of the fundamental life functions. Some animals and plants are of only one cell; other are composed of many, many cells.

Cementation. The manner in which some animals attach or stick themselves to the sea bottom or to other objects.

Cephalon. The head segment of a trilobite.

Chamber. A portion of a shell, separated from another similar portion by a wall or septum, as in the foraminifers or cephalopods.

Chitino-phosphatic. Composed of chitin, a substance similar to fingernails, and calcium phosphate.

Chonetid. Articulate brachiopods, usually concavo-convex, with spines along hinge of pedicle valve, small to medium size; one or more septa in brachial valve. See chonetid brachiopods.

Cilia. Hairlike structures, found on many cells, that can move back and forth.

Circulatory organ. A part of the circulatory system such as the heart and blood vessels.

Cirri. Slender series of plates that outbranch from some crinoid stems.

Coal. A rock composed of carbonaceous material capable of being burned, usually black, derived from plants that have partially decomposed in the absence of air, under pressure and temperature.

Column. The skeletal portion of a crinoid that extends from the base of the dorsal cup to the substrate, also called the stem.

Columnal. One of the plates which, together with other plates, comprises the column of a crinoid.

Commissure. The location where the two valves of a brachiopod or clam come together. See symmetry figure.

Concavo-convex. One valve of a brachiopod is rounded outward outward as the surface of a ball, and the other valve is depressed inward as a bowl.

Concentric. Having the same center. A bullseye is an example of concentric circles.

Concretion. A nodular concentration of mineral matter that, during weathering of the enclosing sedimentary rock, commonly is more resistant and freed as more-or-less rounded rocks. See Neuropteris, a Pennsylvanian plant, and Orbiculoidea, an inarticulate brachiopod.

Conispiral. In mullusks such as snails, having a shell that is coiled in the shape of a cone.

Cord. A thick thread; a pronounced spiral ridge on a snail shell. See the snail Shansiella

Correlate. To tell from evidence found in two or more separated rock units that they are of the same age.

Costae. Ornamental ridges that run from the pointed portion of the shell outward, toward the margins of the valves, but ate not reflected on the interior of the shell. See Aviculopecten, a marine clam.

Costate. Surface of valves bearing costae.

Costella. Thin costae.

Crenella. Fine, radiating ridges on the flat surface of a crinoid columnal.

Crest. Ridge at the center of the whorl of some snails. See Bellerophon snail page.

Crown. The portion of the crinoid skeleton above the column.

Deciduous. Falling off after the growing season, as the leaves of some trees.

Dental sockets. Depressions along the hinge line of a valve shaped to receive the protuding parts (hinge teeth) of the opposite valve.

Discoid. Shaped like a disk.

Dorsal. A direction toward the back or upward side of an organism. The dorsal valve of brachiopods is the brachial valve; dorsal in clams is toward the hinge. See symmetry figure.

Dorsal cup. The cup-shaped skeleton of a crinoid that comprises the body in the lower part of the crown and encloses the vital organs.

Echinoderm. Marine animals having spiny skeletons, including starfishes, echinoids, and crinoids.

Electron microscope. A microscope capable of extremely high magnification, commonly used to view objects too small to be adequately seen through the usual (optical) microscope.

Environment. The surroundings in which an orgamism lives.

Equilateral. Each side equal to the other--refers to brachiopod symmetry. See symmetry figure.

Estuary. An arm of the sea at the mouth of a river.

Facial sutures. The lines along which the cephelon of a trilobite split open when shedding its skeleton, permitting growth

Flagella. Hair-like parts of sponge cells that move to create water currents.

Flute. The wrinkling of a septum. See Baculites cephalopod page.

Fold. The rounded swelling down the center line of many brachiopods, usually on the brachial valve. See symmetry figure.

Foraminifers. Mostly marine, one-celled animals that secrete a chambered or unchambered shell or test, commonly with numerous pores through which pseudopodia extend. See foraminifer page.

Furrow. Shallow groove. See foraminifer or trilobite pages.

Gastropod. Snails and slugs.

Genus. A rank of scientific name used in classifying organisms. The dog has the scientific name Canis familiaris. Canis is the genus.

Geologic. Referring to geology, the study of the earth, its history, and life as recorded in the rocks.

Glabella. Central rounded lobe portion of a trilobite cephalon.

Globose. Globe shaped; rounded or shaped like a ball.

Hinge axis. A line passing through the points of articulation between valves of a clam or brachiopod, along which the valves pivot in opening or closing.

Hinge line. Portion of valve along dorsal margin of clams or posterior margin of brachipods that is permanently in contact with opposite valve, and where valves articulate.

Hinge teeth. Projections from a valve that articulate with the dental sockets in the opposite valve.

Horny. Of a hornlike (chitinous) substance.

Imperforate. Not having perforations, pores, or holes.

Inarticulate. Not having a hinged shell.

Interarea. The flat or curved syrface between the pointed part of a brachipod valve and hinge line along the posterior margin. See Derbyia and Meekella brachiopods.

Ligament. Elastic tissue along the dorsal margin of clams that automatically opens the valves when the adductor muscles are relaxed.

Lignite. Also called brown coal, it is burnable, softer than coal, and has the texture of the original plant fragments preserved.

Limestone. A rock that consists principally of calcium carbonate, commonly derived from an accumulation of the shelly remains of organisms.

Lip. The outer edge of the opening of a snail shell.

Lirae. Fine lines running down the sides of snail shells.

Lobe. A rounded division or portion. See trilobites or chonetid brachiopods.

Locomotion. The ability to move or travel from place to place.

Loess. An accumulation of wind-blown dust.

Loop. A simply bent, non-spiral brachidium. See Beecheria brachiopod.

Lophophore. A feeding organ in brachiopods bearing tentacle-like structures that carry food to the mouth; commonly supported by a brachidium.

Lumen. The central hole in a crinoid columnal.

Margin. Edge; may indicate the outer limits of certain rocks on a geologic map; also the edges of a valve.

Marine. Living in the sea and not in fresh water.

Matrix. The substance of the rock in which a fossil or other object may be enclosed.

Median plane. The imaginary flat surface that divides a feature down the middle and into two equal parts.

Molar. A broad tooth used for grinding rather than for cutting.

Muscle scar. A circular or crescent-shaped area on the inside of brachiopod or clam shells marking where a muscle attached.

Node. A raised area, commonly one that serves as a place of attachment for another structure.

Nodal. A columnal plate bearing nodes for the attachment of cirri. See crinoids.

Non-marine. Living in fresh water and not in the sea.

Oblique. Slanting; not perpendicular.

Organic. That which pertains to living organisms.

Organism. Any living thing.

Orthid. A group of articulate brachiopods having unequally biconvex shells with hinge line parallel to hinge axis and well-developed interareas on both valves; rounded outline, and costate surface.

Oxygenated. Combined with oxygen, or containing dissolved oxygen.

Pallial sinus. Toward posterior inner surface of some clams, an S-shaped line or groove near the margin of valve, marking the space into which tubes (siphons) that draw in food and water and expel waste are withdrawn.

Pedicle. A leathery or muscular stalk that serves to attach a brachiopod to the substrate.

Pedicle beak. The pointed end of the pedicle valve. A small opening through which the pedicle passed may be located near this end. See rhynchonellid brachiopod.

Pedicle valve. The brachiopod valve that contains the pedicle, and is regarded as ventral. See symmetry figure.

Pinnule. The individual leaflets of a fern frond.

Planispiral. The coiling of some snails and cephalopods in which the center of each coil lies in the same plane. See Scaphites cephalopods and the snail page.

Pleural. Refers to the side, thus, one of the lengthwise side lobes of a trilobite.

Plicate. Having folds in the shell that appear on the inside as well as the outside. See Spiriferid brachiopod page.

Polygonal. Many sided.

Porous. Having small holes or pores.

Posterior. Toward the rear, opposite from Anterior. See symmetry figure.

Predaceous. Living by killing and eating other animals.

Productid. Articulate brachiopods with concavo-convex shells, commonly having spines and inconspicuous interareas. See the productid brachiopod page.

Pseudopunctae. False punctae--small rod-shaped structures within the shell of some brachiopods, that commonly appear on the inner surface of the shell as small bumps.

Pygidium. The posterior or tail segment of trilobites, called by some the tail.

Radial. Arranged so that the features extend in all directions from a single point.

Ray. A radial feature, such as the arms of a starfish. Also the sting-ray, a kind of shark having greatly flattened, wing-like bodies (Ptychodus ray).

Rhynchonellid. Articulate brachiopods of small to medium size with biconvex plicate shells, short hinge line, and pointed pedicle beak. See the rhynchonellid brachiopod page.

Secrete. To produce by separating a substance from body fluids. Saliva in our mouths has been secreted by salivary glands.

Sediment. Material such as mud, sand, gravel, calcium carbonate, and salt that are deposited by, or settle out of, water.

Septa. Dividing walls, or partitions (as with corals or cephalopods). Also, a vertical ridge near the middle of a brachiopod valve (chonetid brachiopods).

Shale. A fine-grained sedimentary rock formed from mud and silt, commonly gray to black; tends to split into thin layers.

Siliceous. Contains silica, or silicon dioxide. A common silica mineral is quartz; a common product made principally of silica is glass.

Species. The basic unit of biologic classification. In the Canis familiaris, the common dog, familiaris is the species name. Fossils of the saame species have all distinctive features in common with one another.

Spicules. Small needle-like skeletal parts of sponges. They may be of various shapes from simple rods to stars, and connect to form lattice-like frames. See the sponge page.

Spines. Stiff, sharp, outward-projecting features, as on a porcupine, or on echinoids or brachiopods.

Spiral. Coiled; like the thread of a screw.

Spongin. The flexible material which forms the skeleton of the common bath sponge and which readily decays upon the death of the animal. See the sponge page.

Stalk. An elongate supporting organ.

Stem. A structure resembling the stem of a plant, such as the column of a crinoid.

Strophomenid. Articulate brachiopods that commonly have a hinge equal to greatest width, wider than long, well defined interareas on each valve, pseudopunctate but no spines. See the strophomenid brachiopod page.

Substrate. The mud, sand, rock, or the like that forms the bottom of the sea or estuary.

Sulcus. The rounded depression down the center of many brachiopod shells opposite the fold, commonly on thepedicle valve. See symmetry figure and Echinaria brachiopods.

Tabulae. Floor-like partitions or cross structures found within the skeleton of some kinds of corals. (11)

Tabulate. A coral that has tabulae.

Tegmen. The part of a crinoid above the dorsal cup and within the arms that forms a cover for the vital organs. It may be leathery or consist of plates, and maybe formed into an anal sac.

Terebratulid. Articulate brachiopods with a loop brachidium, endopunctae, commonly subcircular to teardrop shape. See Beecheria brachiopod.

Test. The shell of a foraminifer.

Thoracic. Refers to features found on the thorax, or middle region on a trilobite; the area between the cephalon and the pygidium, comprised of numerous flexible segments.

Thread. Fine thread-like ridges that coil down the outside a snail shell. See snails.

Unchambered. Lacking chambers.

Valve. Either one of the two shells of a brachiopod or a clam.

Ventral. Opposite direction from dorsal, the underside; pedicle pedicle valve of brachiopods. See symmetry figure.

Vertebrae. The bones that form the backbone of higher animals such as fish and mammals.

Whorl. One coil of a coiled shell. See snails.

Please use the "Back" command of your browser to return to the page you were viewing.
Previous Page--Classification of Illustrated Fossils || Next Page--Other Resources
KGS Home Page || Education Index Page

Kansas Geological Survey
Placed online June. 1997
URL = ""
Send comments and/or suggestions to