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Isoxyidae
Isoxyids are members of the order Isoxyida and the family Isoxyidae, a group of basal arthropods that existed during the Cambrian period. It contains two genera, ''Isoxys'', with 20 species found worldwide, and ''Surusicaris'' known from a single species found in the Burgess Shale of Canada. They are distinguished by their bivalved carapaces and pair of upward curving grasping frontal appendages. Description Isoxyids have a combination of features seen in both stem-group arthropods, as well as more advanced taxa. Isoxyids have semicircular bivalved carapaces, large, spherical eyes, a pair of large upward curling frontal appenages covered in spines, and pairs of biramous limbs running along the body. The trunk region appears to be unsegmented and lacks sclerotisation, similar to radiodonts, with a segmented and sclerotised (arthropodized) trunk being characteristic of most arthropods. Currently only two genera have been accepted to be members of this family. These being ''Isox ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isoxys
''Isoxys'' (meaning "equal surfaces") is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes (which are the most commonly preserved feature of the soft-bodied anatomy), and two large frontal appendages used to grasp prey. Description Species of ''Isoxys'' have roughly semicircular bivalved carapaces, which vary in morphology between species. The front and rear edges of the carapaces bear forward and posterior facing spines, respectively which in some species are greatly elongated''.'' The carapaces of ''Isoxys'' are typically in length (with the juveniles of some species being as small as ), excluding the spines, though some species are known to reach over . In long-spined species when including spine length, some specimens exceed . The opening angle of the carapace was close to vertical, giving it a narrow profile when viewed from above.'''' The head had a pair ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surusicaris
''Surusicaris'' is an extinct genus of bivalved arthropod, known from the Cambrian Burgess Shale of British Columbia, Canada. It is considered to be closely related to ''Isoxys,'' and like it has spined grasping frontal appendages. Description The only known specimen (ROM 62976), has a roughly semicircular bivalved carapace, which is approximately long and tall. The head has a pair of rounded eyes, and a pair of upward-curling segmented frontal appendages with at least five segments, the second, third and fourth of which bear a spine, with three long spines and at least one short spine on the fifth and terminal segment. The head also has three pairs of other limbs, which are stubby, uniramous (single-part) and unsclerotised, with an annulated appearance, which are tipped with bifid claws. Along the trunk are 12 pairs of biramous (two-branched) limbs, which taper in size posteriorly. Their morphology is simple, the morphology of the endopod (the inner, leg-like limb branch) is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Holotype
A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several examples, but explicitly designated as the holotype. Under the International Code of Zoological Nomenclature (ICZN), a holotype is one of several kinds of name-bearing types. In the International Code of Nomenclature for algae, fungi, and plants (ICN) and ICZN, the definitions of types are similar in intent but not identical in terminology or underlying concept. For example, the holotype for the butterfly '' Plebejus idas longinus'' is a preserved specimen of that subspecies, held by the Museum of Comparative Zoology at Harvard University. In botany and mycology, an isotype is a duplicate of the holotype, generally pieces from the same individual plant or samples from the same genetic individual. A holotype is not necessarily "ty ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diel Vertical Migration
Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour period. The migration occurs when organisms move up to the uppermost layer of the water at night and return to the bottom of the daylight zone of the oceans or to the dense, bottom layer of lakes during the day. DVM is important to the functioning of deep-sea food webs and the biologically-driven sequestration of carbon. In terms of biomass, DVM is the largest synchronous migration in the world. It is not restricted to any one taxon, as examples are known from crustaceans (copepods), molluscs (squid), and ray-finned fishes (trout). The phenomenon may be advantageous for a number of reasons, most typically to access food and to avoid predators. It is triggered by various stimuli, the most prominent being changes in light-inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pelagic
The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the surface of the sea and the bottom. Conditions in the water column change with depth: pressure increases; temperature and light decrease; salinity, oxygen, micronutrients (such as iron, magnesium and calcium) all change. In a manner analogous to stratification in the Earth's atmosphere, the water column can be divided vertically into up to five different layers (illustrated in the diagram), with the number of layers depending on the depth of the water. Marine life is affected by bathymetry (underwater topography) such as the seafloor, shoreline, or a submarine seamount, as well as by proximity to the boundary between the ocean and the atmosphere at the ocean surface, which brings light for photosynthesis, predation from above, and wind st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown Group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade, a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants. The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen. Contents of the crow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Labrum (arthropod Mouthpart)
The labrum is a flap-like structure that lies immediately in front of the mouth in almost all extant Euarthropoda. The most conspicuous exceptions are the Pycnogonida, which are probably chelicerates. In entomology, the labrum amounts to the "upper lip" of an insect mouth, the corresponding "lower lip" being the labium. The evolutionary origin, embryogenesis, and morphological development of the labrum have proved to be some of the most controversial and challenging topics in the study of arthropod head structures. Embryonic nature and origin of the labrum The labrum is innervated in crustaceans and insects from the tritocerebrum (the back of the brain). However, in development, its embryonic primordium often appears at the anterior of the head and migrates backwards towards its adult position. Furthermore, it often appears as a bilobed structure, with a set of muscles, nerves and gene expression in many ways similar to that of an appendage. This evidence has been used to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypostome (trilobite)
The hypostome is the hard mouthpart of trilobites found on the ventral side of the cephalon (head). The hypostome can be classified into three types based on whether they are permanently attached to the rostrum or not and whether they are aligned to the anterior dorsal tip of the glabella. Morphology The center of the hypostome is an ovoid, typically convex part called the median body, often divided into an anterior lobe and a posterior lobe. Either side of the median body is a border with various extensions, including anterior and posterior wings, sometimes bearing knob-like processes. The hypostome is hollow, and encloses the mouthparts, the anterior digestive tract, and the bases of the antennae. Trilobite antennae pass through notches between the anterior and posterior wings, then forward. The anterior wings are designed to rest firmly against internal structures (ventral apodemes) on the glabella. Variation in trilobite hypostome morphology is crucial in modern discussi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deutocerebrum
The supraesophageal ganglion (also "supraoesophageal ganglion", "arthropod brain" or "microbrain") is the first part of the arthropod, especially insect, central nervous system. It receives and processes information from the first, second, and third metameres. The supraesophageal ganglion lies dorsal to the esophagus and consists of three parts, each a pair of ganglia that may be more or less pronounced, reduced, or fused depending on the genus: * The ''protocerebrum'', associated with the eyes ( compound eyes and ocelli). Directly associated with the eyes is the optic lobe, as the visual center of the brain. * The ''deutocerebrum'' processes sensory information from the antennae. It consists of two parts, the antennal lobe and the dorsal lobe. The dorsal lobe also contains motor neurons which control the antennal muscles. * The ''tritocerebrum'' integrates sensory inputs from the previous two pairs of ganglia. The lobes of the tritocerebrum split to circumvent the esophagus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population, or a species (extinct or Extant taxon, extant). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed ''monophyletic'' (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming Taxon, taxa that are not clades; that is, taxa that are not Monophyly, monophyletic. Some of the relationships between organisms that the molecul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hymenocarina
Hymenocarina is an Order (biology), order of extinct marine arthropods known from the Cambrian. They possess bivalved carapaces, typically with exposed posteriors. Members of the group are morphologically diverse and had a variety of ecologies, including as filter feeders and as predators. Recent research has generally considered them to be stem or crown group members of Mandibulata, due to the presence of Mandible (arthropod mouthpart), mandibles in well-preserved species. Taxonomy Hymenocarines are characterized by the combination of the following characters: bivalved, convex carapace covering Cephalothorax, cephalothoracic (combined head and thorax) region; cephalothorax bearing multisegmented antennae (though as an exception antennae are absent in ''Odaraia'') and rounded Mandible (arthropod mouthpart), mandibles and likely Maxilla (arthropod mouthpart), maxillae, post maxillae limbs with spiny, subdivided basis and Arthropod leg, endopods (lower, leg-like parts) with well-d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tuzoia
''Tuzoia'' (from Mount Tuzo, a mountain in the Canadian Rockies) is an extinct genus of large bivalved arthropod known from Early to Middle Cambrian marine environments from what is now North America, Australia, China, Europe and Siberia. The large, domed carapace reached lengths of , making them amongst the largest known Cambrian arthropods. Description The largest carapaces of ''Tuzoia'' are known to reach in length, suggesting a total body length of approximately . Along the sides of the carapace a spiked ridge is present, and the edges and midline of the carapace are also spiked in many species. These spines likely functioned to aid stability while swimming. The carapaces are marked with a reticulate (net-like) pattern, which was likely to increase the structural integrity of the valves while remaining lightweight. The head had a anterior/ocular sclerite at the top, a single pair of large stalked eyes, and a pair of segmented antennae. The head also bore pairs of cephalic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
