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Great Appendage
Megacheira ("great hands", also historically great appendage arthropods) is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either considering them stem-group euarthropods, or stem-group chelicerates. The homology of the great appendages to the cephalic appendages of other arthropods is also controversial. Uncontested members of the group were present in marine environments worldwide from the lower Cambrian to the upper Ordovician. Morphology Megacheirans are defined by their possession of uniramous "great appendages", which are their first pair of head appendages. The first one or two proximalmost segments/ podomeres are spineless (it has been argued that the supposed first of the two proximal podomeres is actually an arthrodial membrane), while the remaining 3–4 more distal podomeres each typically bear a single upward pointing spine attached towards the distal en ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alalcomenaeus
''Alalcomenaeus'' is one of the most widespread and longest-surviving arthropod genera of the Early and Middle Cambrian. Known from over 300 specimens in the Burgess Shale and the Chengjiang biota. It is a member of the family Leanchoiliidae in the group Megacheira. Morphology ''Alalcomenaeus'' had three median eyes; two stalked, more lateral eyes; a triflagellate great appendage; and two more head appendages posterior to that. Like its body appendages, these were biramous—their inner branch was spiny, segmented, flexible and leg-like, while the outer portion had a large surface area and resembled a flap. ''Alalcomenaeus'' reached about 6 cm in length, although many smaller specimens are known. Its head was covered with a shield, and its eleven body segments were also covered with an exoskeleton. Its body terminated with a paddle-like telson ("tail") which probably helped to propel the organism; this ended with long flat spikes in the plane of the tail fin. Ecology T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Raptorial
In biology (specifically the anatomy of arthropods), the term ''raptorial'' implies much the same as ''predatory'' but most often refers to modifications of an arthropod leg, arthropod's foreleg that make it function for the grasping of prey while it is consumed, where the gripping surfaces are formed from the opposing faces of two successive leg Segmentation (biology), segments (''see illustration''). This is distinctly different from the grasping mechanism of a structure such as a scorpion's claw (a "Chela (organ), chela") in which one of the opposing surfaces is an articulated digit, and not a leg segment. While this is most widely known in Mantodea, mantises, similarly modified legs can be found in some crustaceans (e.g., mantis shrimp), and various insect families, such as Mantispidae, Belostomatidae, Nepidae, and Naucoridae (all members of these groups have raptorial forelegs). There are numerous other lineages within various insect families that have raptorial forelegs, mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lomankus
''Lomankus'' is an extinct genus of megacheiran (great appendage) arthropod known from the upper Ordovician aged Beecher's Trilobite Bed, within the larger Frankfort shale in the state of New York (state), New York. A single species is known, ''Lomankus edgecombei'', which was described by Parry ''et al''., 2024. It is currently placed within the family Megacheira, Leanchoiliidae, within the larger Leanchoilida order, and represents the youngest known member of the group. Members of this family are characterized by the presence of long flagelliform structures on their frontal appendages, which were most likely used for both sensory and raptorial purposes. ''Lomankus'' is significant, as it represents the youngest known definitive megacheiran in the fossil record, as well as the only definitive member of the order from post-Cambrian strata. Although several other genera of post-Cambrian arthropods, including members of the family Enaliktidae, have been proposed as members of megach ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In contrast, a monophyletic grouping (a clade) includes a common ancestor and ''all'' of its descendants. The terms are commonly used in phylogenetics (a subfield of biology) and in the tree model of historical linguistics. Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies. If many subgroups are missing from the named group, it is said to be polyparaphyletic. The term received currency during the debates of the 1960s and 1970s accompanying the rise of cladistics, having been coined by zoologist Willi Hennig to apply to well-known taxa like Reptilia (reptiles), which is paraphyletic with respect to birds. Reptilia contains the last common ancestor of reptiles and all descendants of that ancestor exc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monophyly
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent common ancestor (or more precisely an ancestral population), i.e. excludes non-descendants of that common ancestor # the grouping contains all the descendants of that common ancestor, without exception Monophyly is contrasted with paraphyly and polyphyly as shown in the second diagram. A ''paraphyletic'' grouping meets 1. but not 2., thus consisting of the descendants of a common ancestor, excepting one or more monophyletic subgroups. A ''polyphyletic'' grouping meets neither criterion, and instead serves to characterize convergent relationships of biological features rather than genetic relationships – for example, night-active primates, fruit trees, or aquatic insects. As such, these characteristic features of a polyphyletic grouping are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parapeytoia
''Parapeytoia'' is a genus of Cambrian arthropod. The type and only described species is ''Parapeytoia yunnanensis'', which lived over 518 million years ago (Cambrian Stage 3) in the Maotianshan shales of Yunnan, China. Unidentified fossils from the same genus have also been discovered from the nearby Wulongqing Formation ( Cambrian Stage 4). Classification Initially, ''Parapeytoia'' was interpreted as a radiodont ("anomalocaridid" at that time) dinocaridid with legs alongside '' Cucumericrus'', purported to be an indicator that radiodonts might have legs underneath their body flaps in general, comparable to '' Pambdelurion''. With the combination of megacheiran and presumably radiodont features (see text), it was also suggested to be an intermediate form between the two taxa. However, later studies revealed it was most likely nested within megacheira, and the group as a whole was no longer thought to have originated from radiodonts. Within megacheira, ''Parapeytoia'' was po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sklerolibyon
''Sklerolibyon'' is an extinct genus of megacheiran marine arthropod, known from the Cambrian aged Chengjiang biota of Yunnan, China. It is a member of the family Jianfengiidae, alongside '' Jianfengia'' and '' Fortiforceps,'' and possibly also ''Parapeytoia''. Specimens are around in length. The body is greatly elongated, and head shield is heavily sclerotised, with a pair of spines radiating outward from the sides. Alongside the pair of great appendages, there are a pair of stalked eyes and at least two other pairs of limbs on the cephalon. The trunk has 34 segments with corresponding biramous appendages, with typically megacheiran paddle-shaped exopods. The tail is unknown but like ''Jianfengia'' probably ended in a telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ... spin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jianfengia
''Jianfengia'' is an extinct genus of Middle Cambrian (Atdabanian) megacheiran arthropod found in the Maotianshan Shale Lagerstätte of China. It contains the single species ''Jianfengia multisegmentalis''.''Jianfengia'' in the The body is extremely elongated, though the animal itself was relatively small at less than in length. The head has a pair of stalked eyes, a hypostome/ labrum complex, a pair of [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exite
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, : ''coxae''), ''trochanter'', ''femur'' (: ''femora''), ''tibia'' (: ''tibiae''), ''tarsus'' (: ''tarsi''), ''ischium'' (: ''ischia''), ''metatarsus'', ''carpus'', ''dactylus'' (meaning finger), ''patella'' (: ''patellae''). Homologies of leg segments between groups are difficult to prove and are the source of much argument. Some authors posit up to eleven segments per leg for the most recent common ancestor of extant arthropods but modern arthropods have eight or fewer. It has been argued that the ancestral leg need not have been so complex, and that other events, such as successive loss of function of a ''Hox''-gene, could result in parallel gains of leg segments. In arthropods, each of the leg segments articulates with the next segme ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telson
The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segment on account of not arising in the embryo from teloblast areas as other segments. It never carries any appendages, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups. Crustaceans In lobsters, Caridea, shrimp and other Decapoda, decapods, the telson, along with the uropods, forms the tail fan. This is used as a paddle in the caridoid escape reaction ("lobstering"), whereby an alarmed animal rapidly flexes its tail, causing it to dart backwards. Krill can reach speeds of over 60 cm per second by this means. The Induction period, trigger time to optical stimulus (physiology), stimulus is, in spite of the low temperatures, only 55 milliseconds. In th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exopod
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip (anatomy), hip, : ''coxae''), ''trochanter'', ''femur'' (: ''femora''), ''tibia'' (: ''tibiae''), ''tarsus'' (: ''tarsi''), ''ischium'' (: ''ischia''), ''metatarsus'', ''carpus'', ''dactylus'' (meaning finger), ''patella'' (: ''patellae''). Homology (biology), Homologies of leg segments between groups are difficult to prove and are the source of much argument. Some authors posit up to eleven segments per leg for the most recent common ancestor of Neontology, extant arthropods but modern arthropods have eight or fewer. It has been argued that the ancestral leg need not have been so complex, and that other events, such as successive loss of function of a Homeobox, ''Hox''-gene, could result in Parallel evolution, parallel gains of leg segments ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
