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Megacheira
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] |
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] |
Arthropod
Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metamerism (biology), metameric) Segmentation (biology), segments, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They form an extremely diverse group of up to ten million species. Haemolymph is the analogue of blood for most arthropods. An arthropod has an open circulatory system, with a body cavity called a haemocoel through which haemolymph circulates to the interior Organ (anatomy), organs. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. They have ladder-like nervous systems, with paired Anatomical terms of location#Dorsal and ventral, ventral Ventral nerve cord, nerve cord ... [...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] |
Leanchoilia
''Leanchoilia'' is a megacheiran marine arthropod known from Cambrian deposits of the Burgess Shale in Canada and the Chengjiang biota of China. Description ''L. superlata'' was about long and had long, whip-like flagellae extending from its great appendages. Its internal organs are occasionally preserved within the substrate in three dimensions. Their two pairs of eyes are protected and covered by their exterior head shields, with two eyes being located on each side. Species Seven species are tentatively accepted today: ''L. superlata'' (the type species), ''L. persephone'' and ''L. protogonia'' from the Burgess Shale, ''L. illecebrosa'' and ''L. obesa'' from the Chengjiang biota, 'L. robisoni'' from Kaili, and ''L.''? ''hanceyi'' from the Spence Shale. ''L. superlata'' and ''L. persephone'' may however be examples of sexual dimorphism. Distribution 55 specimens of ''Leanchoilia'' are known from the Greater Phyllopod bed, where they comprise 0.1% of the community. S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yohoia
''Yohoia'' is an extinct genus of megacheiran arthropod from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. The type species, ''Yohoia tenuis'', was described in 1912 by Walcott, who considered it an anostracan crustacean. 711 specimens of ''Yohoia'' are known from the Greater Phyllopod bed, where they comprise 1.35% of the community. In 2015, Conway Morris ''et al.'' reported another species, ''Y. utahana'', from the Marjum Formation, Utah. Description Fossil specimens of ''Yohoia'' range in size from 7 to 23 mm, they have a head shield which is followed by 13 trunk tergites, or plates. On both sides, the bottom side of the first 10 of these ended in backward-pointing, triangular points or projections. The last three plates were complete tubes, circling the entire trunk. At the end of the trunk was a paddle-like tail. There were also a pair of large extensions at the front of the head shield. They had ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fortiforceps
''Fortiforceps'' is an extinct genus of Cambrian megacheiran marine arthropod known from the Chengjiang biota of Yunnan, China. It was originally described by Hou and Bergström in 1997, and redescribed in 2020. It was relatively small, at or less in length. The head had a pair of large, stalked eyes, a pair of frontal projections, as well as a pair of great appendages, like other megacheirans, along with two other cephalic appendages. The trunk had either 20 or 22 segments, depending on the specimen. These segments had pronounced blade-like spines on their upper-outer edge. Each of the trunk segments (aside from the last, typically 20th segment) were associated with pairs of biramous limbs, which probably have seven podomeres and like other megacheirans, have paddle-shaped exopods. The trunk terminated with a forked tailpiece, which on their outer edges had rod-like structures. The two lobes were separated by a rectangular central piece. It has been placed as a member of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yawunik
''Yawunik'' is an extinct genus of Cambrian megacheiran ("Great appendage" arthropod) known from the Burgess Shale in Canada ( Marble Canyon locality). The type species has been named ''Yawunik kootenayi'' after the Kootenay, both a geographic area (and National Park, where the fossil was found) and North American First Nation, also known as the Ktunaxa. The genus name is derived from , the name of a primordial sea monster in Ktunaxa mythology. The fossil dates back to 508 million years ago. Description ''Yawunik'' was large for a megacheiran, up to long not including the great appendages. It had four eyes; two in the anteriormost position of the head, as well as lateral eyes which were larger. ''Yawunik'' differs from other leanchoilids such as ''Leanchoilia ''Leanchoilia'' is a megacheiran marine arthropod known from Cambrian deposits of the Burgess Shale in Canada and the Chengjiang biota of China. Description ''L. superlata'' was about long and had long, whip- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiodont
Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety of functions. Radiodonts were among the earliest large predators, but they also included sediment sifters and filter feeders. Some of the most famous species of radiodonts are the Cambrian taxa ''Anomalocaris canadensis'', '' Hurdia victoria'', ''Peytoia nathorsti'', '' Titanokorys gainesi, Cambroraster falcatus'' and '' Amplectobelua symbrachiata''. The later surviving members include the subfamily Aegirocassisinae from the Early Ordovician of Morocco and the Early Devonian member '' Schinderhannes bartelsi'' from Germany. Etymology The name Radiodonta (Latin for ''radius'' "spoke of a wheel" and Greek for ''odoús'' "tooth") refers to the radial arrangement of tooth plates (oral cone) surrounding the mouth, although this feature is su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chelicerata
The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks, and mites, among many others), as well as a number of extinct lineages, such as the eurypterids (sea scorpions) and chasmataspidids. Chelicerata split from Mandibulata by the mid-Cambrian, as evidenced by stem-group chelicerates like Habeliida and '' Mollisonia'' present by this time. The surviving marine species include the four species of xiphosurans (horseshoe crabs), and possibly the 1,300 species of pycnogonids (sea spiders), if the latter are indeed chelicerates. On the other hand, there are over 77,000 well-identified species of air-breathing chelicerates, and there may be about 500,000 unidentified species. Like all arthropods, chelicerates have segmented bodies with jointed limbs, all covered in a cuti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haikoucaris
''Haikoucaris'' is a genus of megacheiran arthropod that contains the single species ''Haikoucaris ercaiensis''. It was discovered in the Cambrian Chengjiang biota of China. Morphology ''Haikoucaris'' measured about 38 mm in body length. The elongated body compose of a semicircular head shield, 13 trunk tergites and presumely a short, spine-like telson. The head possess a pair of unstalked eyes, a pair well-developed great appendages, as well as 3 more appendage pairs of unknown detail. Each of the great appendage consists of a 2-segmented peduncle and a 3-segmented claw. Each of the trunk segment possess a pair of biramus appendages that each comprising a leaf-shaped exopod and a possibly 7-segmented endopod. Paleoecology ''Haikoucaris'' may have been a predator, with its great appendages and exopod suggested to be used for hunting and swimming respectively. Taxonomy Within megacheirans, ''Haikoucaris'' is generally accepted to be a member of the clade Cheiromorpha alongs ... [...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] |
