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from article Patellogastropoda
Whitecap limpet (Acmaea mitra). (Photo by Douglas Eernisse)
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from article Patellogastropoda
Ribbed Mediterranean limpet (Patella ferruginea). (Photo by Georgina Rivera Ingraham)
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from article Patellogastropoda
Radula of the patellogastropod Notoacmea scapha.
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from article Sauropterygia
Ceresiosaurus calcagnii, ventral view.
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from article Corallinales
Articulated coralline red algae (genus Calliarthron, order Corallinales) found off the California coast in the Pacific Ocean. (Photo by Steve Lonhart, Monterey Bay National Marine Sanctuary, National Oceanic and Atmospheric Administration)
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from article Model theory
Conceptual model of a system.
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from article Model theory
Model of a regional population system.
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from article Aspidorhynchiformes
Aspidorhynchus acutirostris, Upper Jurassic, Bavaria; a typical fish of the order Aspidorhynchiformes.
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from article Paleobotany
Compression specimen of the Triassic leaf type Dicroidium.
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from article Paleobotany
Permian pollen grain macerated from Antarctic coal.
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from article Paleobotany
Cross section of a permineralized stem from a Carboniferous coal ball.
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from article Paleobotany
Thin section of a petrified Rhynie chert stem.
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from article Paleobotany
Several coprolites found within the tissues of a Carboniferous plant.
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from article Paleobotany
Cuticle of a fossil (Eocene) leaf showing the outline of the epidermal cells and fungus with specialized hyphae.
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from article Paleobotany
Several Glossopteris leaves from the Permian of Antarctica. Leaves of this type were some of the first evidence that at one time the southern continents were all physically linked into a major continental plate called Gondwana.
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from article Paleobotany
Section showing tree rings from a temperate plant, showing change in cell size and wall thickness.
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from article Paleobotany
Section showing rings from a tree with uniform cell size and wall thickness, but growing at approximately 82° South during the Triassic.
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from article Osteolepiformes
Schematic phylogeny (family tree) of the osteolepiforms, based on arguments presented by P. Ahlberg and Z. Johanson (1998). The fishes within the gray zone are conventionally designated as Osteolepiformes (the formal group name), but they actually…
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from article Osteolepiformes
The tristichopterid Eusthenopteron foordi. (a) A close-up of its pectoral fin skeleton. (b) An illustration of the full specimen. Eusthenopteron reached approximately 50–70 cm in length. Its pectoral fin skeleton contains structures equivalent to…
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from article Sphaeractinoidea
Sphaeractinoid Actinostromaria rhodaclada, Cretaceous, Jura Mountains: (a) tangential and (b) longitudinal section, ×6. (From A. Steiner, 1932)
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from article Lissamphibia
Pedicellate teeth in Lissamphibia: (a) salamander; (b) apodan; (c) frog. Teeth are from the lower jaw (a, b) or upper jaw inverted (c) and are viewed from inside the mouth. (After T. Parsons and E. E. Williams, The teeth of Amphibia and their…
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from article Lissamphibia
Operculum-stapes complex of a primitive salamander (skin removed to show internal structures).
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from article Crustacea
Some crustaceans in their respective habitats, mostly reduced but not to same scale. Orders are in parentheses. (a) Marine forms and common names: Pollicipes, goose barnacle; Balanus, acorn barnacle; Mysis, opossum shrimp; Orchestia, sand hopper;…
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from article Crustacea
Diagram of the fifth pleonal somite of the crayfish, with its paired fifth pleopods.
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from article Crustacea
External morphology of a shrimp. (After P. A. McLaughlin, Comparative Morphology of Recent Crustacea, W. H. Freeman, 1980)
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from article Crustacea
Cephalic and thoracic appendages of representative crustaceans: (a–d) antennules; (e–h) mandibles; (i–l ) thoracopods. (a) Brachypoda; (b) Leptostraca; (c, d) Decapoda; (e) Brachypoda; (f) Stomatopoda; (g) Mysida; (h) Decapoda; (i) Anostraca; (j)…
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from article Crustacea
Nauplii of (a) Triops cancriformis (Notostraca); (b) Branchinecta occidentalis (Anostraca); (c) Lernaeocera branchialis (Siphonostomatoida); (d) Haemocera danae (Monstrilloida); (e) Meganyctiphanes norvegica (Euphausiacea); (f) Sacculina carcini…
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from article Crustacea
Larval stages of representative crustaceans: (a) cyprid larva of Sessilia; (b) pseudolarva of Stomatopoda; (c) phyllosoma larva of Decapoda; (d) zoeal larva of Decapoda; (e) megalopa of Decapoda. (After P. A. McLaughlin, Comparative Morphology of…
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from article Crustacea
Chart of the classification of Crustacea; no indication of phylogenetic relationships is implied. (Modified from D. E. Bliss, ed., The Biology of Crustacea, vols. 1–10, Academic Press, 1982–1985)
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from article Crustacea
Late Devonian malacostracan Palaeopalaemon newberryi Whitfield, considered to be the earliest decapod crustacean. (After F. R. Schram, R. M. Feldmann, and M. J. Copeland, J. Paleontol., 52:1381, 1978)
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from article Glyptodont
A glyptodont skeleton belonging to the type genus, Glyptodon. (Credit: Gyik Toma)
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from article Glyptodont
Reconstruction of Glyptotherium texanum from Arizona. (Credit: David D. Gillette; illustration by Bonnie Dalzell)
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from article Glyptodont
Hexagonal osteoderm (a protective bony plate) in (top) lateral view and (bottom) external view. (Credit: David D. Gillette)
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from article Glyptodont
Cutaway interpretation of the osteology (skeletal and bone structure) of Glyptotherium. (Credit: Larry Isham)
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from article Echinodermata
Cross section through the spine of an echinoid showing the microscopic structure of the skeleton. The stereom forms a continuous mesh, and the stroma that secretes it lies in the interspaces which, in this case, are arranged in radial rows.
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from article Echinodermata
Diagram of the water-vascular system in an echinoid. Arrows show direction of fluid flow.
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from article Echinodermata
General scheme indicating relationships of bilaterally symmetrical echinoderm larvae. (After H. B. Fell)
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from article Echinodermata
Echinoderms in the deep sea near Antarctica at a depth of 595 m (1950 ft). Three sea cucumbers (Scotoplanes globosa) are feeding on seafloor sediments. At bottom right is a brittle star, probably Ophiomusium species. Scattered on the seafloor but…
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from article Echinodermata
Representative types of echinoderms. (a) Regular echinoid (Lytechinus, Recent), oblique aboral view, right half with spines removed, showing two ambulacra and three interambulacra. (b) Diagrammatic section through a, showing the stoutly built test.…
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from article Echinodermata
Fossil pelmatozoan echinoderms. (a) Rhombiferan cystoid (Echinoencrinus, Ordovician). (b) Diagrammatic oblique view and section through a cystoid pore rhomb (half of one rhomb toward front bisected by a suture between plates). (c) Oblique view and…
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from article Echinodermata
Bilateral symmetry developed in various echinoderms. Anterior and posterior directions are indicated where distinguished. All diagrams represent aboral views. (a) Crinozoans (in general, most crinoids, cystoids, edrioasteroids); letters denote ray…
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from article Echinodermata
Fossil echinoids. (a) Regular form (Echinocrinus, Mississippian), aboral view showing the anus and periproct, wide interambulacra and narrow ambulacra. (b) Irregular form (Eupatagus, Paleogene), aboral view, left side showing an unweathered…
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from article Echinodermata
Phylogeny and diversity range chart for the Paleozoic echinoderms. (After C. R. C. Paul and A. B. Smith, The early radiation and phylogeny of echinoderms, Biol. Rev., 59:443–481, 1984)
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from article Physical vapor deposition
Processes for generation of depositing species within vacuum chambers. (a) Evaporation deposition process using an electron-beam evaporation source. (b) Sputter deposition process.
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from article Physical vapor deposition
Alloy deposition by evaporation. (a) Two-source (A and B) evaporation arrangement yielding variable film composition. T1, T2, and T3 are temperatures of A, B, and substrate, respectively. (b) Direct evaporation of an alloy from a single rod-fed…
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from article Foraminiferida
Scanning electron micrographs of foraminiferans of suborder Textulariina. Superfamily Ammodiscacea: (a) Ammodiscus, a planispirally enrolled, fine-grained agglutinated test, from Silurian of Missouri. Superfamily Astrorhizacea: (b) Thurammina, a…
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from article Foraminiferida
Scanning electron micrographs of foraminiferans of suborder Miliolina. Superfamily Alveolinacea: (a) Alveolinella, an isomorph of the microgranular fusulines, but with porcelaneous wall; abraded surface shows the many tiny chamberlets; apertural…
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from article Foraminiferida
Scanning electron micrographs of foraminiferans of suborder Fusulinina. Superfamily Eardlandiacea: Earlandia, from Pennsylvanian of Texas: (a) side view of elongate, undivided tubular test; (b) surface of wall, which is composed of tiny angular…
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from article Ctenothrissiformes
A Cretaceous ctenothrissiform fossil, Ctenothrissa sp. (order Ctenothrissiformes), on a limestone matrix found in Lebanon. Size: 90 mm (3.5 in.). (Photo courtesy of The Virtual Fossil Museum)
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from article Animal testing
Mice are the most commonly used vertebrate species in animal testing and research. (Credit: Dolores Bonaparte)
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from article Animal testing
The use of animals in biomedical research remains essential, but the handling of these sentient beings must be done humanely to minimize and prevent animal harm. (Credit: U.S. Department of Agriculture)
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from article Chicxulub impact crater
Bouguer gravity anomaly map over the Chicxulub impact crater. The coastline is designated by a thin white line, cenotes (natural pits) and sinkholes are designated by black dots, and the city of Mérida and the town of Chicxulub Puerto are designated…
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from article Chicxulub impact crater
Seismic line imaging of what lies beneath the seafloor, showing the Chicxulub impact crater. The crater includes many faults that can be grouped into an exterior ring fault, a series of outer ring faults, and a series of inner ring faults. Within…
Image
from article Graptolithina
Sketches of portions of pterobranch and graptolite colonies showing the dwelling tubes and the constructional units of the graptolite skeleton. (a) Young Rhabdopleura compacta colony with founder zooid and first asexual bud (Recent). Benthic…
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from article Graptolithina
Scanning electron micrograph of a graptolite (Pseudoclimacograptus scharengergi) showing the fuselli (horizontal ridges) that compose graptolite thecae, and the cortical bandages (oblique strips) that were deposited on top of the fuselli (Middle…
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from article Graptolithina
Hypothetical form of zooids that inhabited colony tubes, based on a planktic graptolite. Large zooids are shown with possible oarlike swimming organs used to move the colony through the ocean water and tentacles for feeding. Also shown are two…
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from article Graptolithina
Examples of some planktic graptolites, reconstructed to show three-dimensional form.
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from article Cyclostomatida
Cyclostome zooids (order Cyclostomatida) with tentacles retracted versus extended. (Reprinted with permission from R. J. Cuffey and J. E. Utgaard, Bryozoans, pp. 201–216, in R. Singer, ed., Encyclopedia of Paleontology, Vol. 1, 2d ed., Fitzroy…
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from article Xenungulata
Molars of Carodnia vieirai from the Paleocene of Brazil: (a) upper and (b) lower.
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from article Porifera
The giant barrel sponge (Xestospongia muta) is often found growing on Caribbean coral reefs. This type of marine sponge, which belongs to the class Demospongiae, has been known to grow to more than 1.8 m (6 ft) in diameter. (Credit: National Oceanic…
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from article Porifera
The azure vase (chalice) sponge (Callyspongia plicifera) is a type of demosponge, producing monaxonic or tetraxonic silica spicules and/or spongin. (Credit: Diane R. Nelson)
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from article Porifera
Diagram of the canal system of a young freshwater sponge. (Copyright © McGraw-Hill Education)
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from article Porifera
Cell types found in a freshwater sponge as seen in a cross section through the interior of the sponge. (Copyright © McGraw-Hill Education)
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from article Porifera
Diagram of a flagellated chamber of a freshwater sponge. The chamber is shown in optical section, and the exhalant canal is shown in three dimensions. (Copyright © McGraw-Hill Education)
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from article Porifera
Spicule types. Monaxons: (a) monactinal; (b) diactinal. Tetraxons: (c) equirayed; (d) triaene. (e) Triradiate. (f) Triaxon or hexactine. (g) Microscleres. (Copyright © McGraw-Hill Education)
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from article Porifera
Carrier cell transmitting sperm to egg in a calcareous sponge. (Copyright © McGraw-Hill Education)
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from article Porifera
Sponge gemmules (asexual reproductive bodies): (a) freshwater sponge gemmules in optical section; (b) marine siliceous sponge gemmules (surface view). (Copyright © McGraw-Hill Education)
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from article Porifera
Zoanthids living in a sponge. (Copyright © McGraw-Hill Education)
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from article Porifera
A fossilized early sponge. (Credit: Yinan Chen)
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from article Spongiomorphida
Spongiomorpha acyclica (Triassic, Austria), length = 8 cm. (From J. P. Smith, Upper Triassic marine invertebrate faunas of North America: Spongiomorphs, U.S. Geol. Surv. Prof. Pap., 1927)
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from article Octopoda
An octopod swimming in the ocean. (Credit: Getty Images/iStockphoto)
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from article Octopoda
Hapalochlaena maculosa, the Southern or lesser blue-ringed octopus, displaying vivid, small blue rings on its body and arms, highlighted with black outlines. Location: Mrs. Watson's Bay, Lizard Island, Great Barrier Reef, Australia. (Credit:…
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from article Octopoda
Hapalochlaena fasciata, the blue-lined octopus, displaying vivid blue lines on its body and rings on its arms, highlighted with black outlines. Location: Long Reef, New South Wales, Australia. (Credit: Copyright © Clyde F. E. Roper)
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from article Octopoda
Lateral view of a female Argonauta (family Argonautidae).
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from article Polyplacophora
Chiton on a rock surface. (Photo courtesy of the NOAA Okeanos Explorer Program, National Oceanic and Atmospheric Administration)
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from article Polyplacophora
Polyplacophoran mollusk (chiton): (a) dorsal view; (b) ventral view.
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from article Trace fossils
Domichnial dwelling burrow with pelleted wall, probably created by a burrowing crustacean. Ophiomorpha, Cretaceous, North Dakota. (From W. Häntzschel, in C. Teichert, ed., Treatise on Invertebrate Paleontology, pt. W, revised, University of Kansas…
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from article Trace fossils
Highly branched, fodinichnial mining burrow, possibly produced by a deposit-feeding crustacean or worm. (a) Chondrites, Tertiary, Austria. (b) Chondrites, Tertiary, Spain. (From W. Häntzschel, in C. Teichert, ed., Treatise on Invertebrate…
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from article Trace fossils
Agrichnial farming trace of an unknown organism, composed of a hexagonal, meshlike network of tunnels. Paleodictyon, Tertiary, Poland. (Photograph by W. Häntzschel)
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from article Trace fossils
Agrichnial farming traces of unknown organisms, including a double-spiral tunnel (Spirorhaphe) and a meshlike network of tunnels (Paleodictyon). Tertiary, Austria. (Photograph by W. Häntzschel)
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from article Trace fossils
Loosely meandering, agrichnial farming trace of an unknown organism. Cosmorhaphe, Tertiary, Poland. (From W. Häntzschel, in C. Teichert, ed., Treatise on Invertebrate Paleontology, pt. W, revised, University of Kansas Press, 1975)
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from article Trace fossils
Praedichnial boring drilled in a bivalve shell by a carnivorous gastropod. Oichnus, Recent, Texas. (Photograph by A. A. Ekdale)
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from article Trace fossils
Tightly meandering, pascichnial grazing trail, created by an unknown worm. Helminthoida, Tertiary, Austria. (From W. Häntzschel, in C. Teichert, ed., Treatise on Invertebrate Paleontology, pt. W, revised, University of Kansas Press, 1975)
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from article Trace fossils
Repichnial trail of an arthropod, possibly a trilobite. Cruziana, Cambrian, Alberta. (Photograph by J. P. A. Magwood)
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from article Trace fossils
Unnamed escape structure (fugichnial trace) in sandstone. Cretaceous, Utah. (Photograph by A. A. Ekdale)
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from article Trace fossils
Cubichnial resting trace of an ophiuroid brittle star. Asteriacites, Jurassic, Germany. (Photograph by W. Häntzschel)
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from article Trace fossils
Complex, composite ichnofabric created by numerous successive phases of burrowing in a fine-grained pelagic carbonate deposit, which has been weakly cemented to become chalk. Upper Cretaceous, Denmark. (Photograph by A. A. Ekdale and R. G. Bromley)
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from article Neandertals
Neandertal cranium excavated from Forbes' Quarry, Gibraltar. Note the pronounced brow ridges, large braincase, and receding forehead. (Photo courtesy of Clive Finlayson, Gibraltar Museum)
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from article Neandertals
Gorham's Cave, Gibraltar, is the last known site of Neandertal occupation, being dated possibly to 30,000 years ago. (Photo courtesy of Clive Finlayson, Gibraltar Museum)
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from article Neandertals
Reconstructed skull of a Neandertal from the cave at La Chapelle-aux-Saints, France. (Illustration adapted from an original drawing by M. F. Ashley Montagu)
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from article Monoplacophora
Living and fossil Monoplacophora. (a) Neopilina galatheae. (b) Tryblidium reticulatum. (After R. C. Moore, ed., Treatise on Invertebrate Paleontology, pt. I, 1957)
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from article Monoplacophora
Side views of various helcionellacean and bellerophont univalved mollusks. (a) Cyrtonellopsis; (b) Hypseloconus; (c) Cyclocyrtonella; (d) Stenotheca; (e) Bellerophon; (f) Tropidodiscus. (After B. Runnegar, Class Monoplacophora, in R. S. Boardman, A.…
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from article Heterocorallia
Morphology of the heterocorallian skeleton. (a) External view. (b) Transverse thin section. (c) Median longitudinal thin section. (d) Enlarged part of c. (After R. C. Moore, ed., Treatise on Invertebrate Paleontology, pt. F, Geological Society of…
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from article Heterocorallia
Details of the heterocorallian body. (a) Generalized pattern of septal insertion (from O. Schindewolf, Grundfragen der Paläontologie, Schweizerbart, Stuttgart, 1950). (b) Reconstruction of the mesenterial in the soft body (from M. Gudo,…
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from article Selachii
Caribbean reef shark (Carcharhinus perezi), a species of ground shark. (Getty Images copyright © Digital Vision)
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from article Insectivora
Buena Vista Lake ornate shrew (Sorex ornatus relictus) sitting on the palm of a hand. (Photo courtesy of California State University, Stanislaus; and the U.S. Fish and Wildlife Service)
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from article Insectivora
Reconstruction of Deinogalerix, an extinct giant insectivore (erinaceid) from the Miocene of Italy. (Adapted from M. Freudenthal, Deinogalerix koenigswaldi nov. gen., nov. spec., a giant insectivore from the Neogene of Italy, Scr. Geol., 14:1–19,…
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from article Insectivora
Skull of Kennalestes, an extinct proteutherian from the Cretaceous of Mongolia.
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from article Caprimulgiformes
Puerto Rican nightjar (Caprimulgus noctitherus). (Photo by Mike Morel, U.S. Fish and Wildlife Service)
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from article Chevrotain
Water chevrotain (Hyemoschus aquaticus). (Photo by Brent Huffman; courtesy of Ultimate Ungulate)
