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Hymenocarina
Hymenocarina is an order of extinct 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 the presence of mandibles in at least some species. Taxonomy Hymenocarines are characterized by the combination of following characters: bivalved, convex carapace covering cephalothoracic region; cephalothorax bearing multisegmented antennules and rounded mandibles, alongside post-maxillular limbs with spiny, subdivided basis and endopods with well-developed terminal claws; absence of appendages between antennules and mandibles; median sclerite and lobate protrusions located between compound eyes; posterior tagma (abdomen) with ring-like segments and terminated by a pair of well-developed caudal rami. Based ...
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Nereocaris
''Nereocaris'' is an extinct genus of bivalved hymenocarine arthropod that lived in the Cambrian aged Burgess Shale in what is now British Columbia around 506 million years ago. Two species are known. History and nomenclature The holotype and paratype were found in the Burgess Shale Läggerstatte, in the Tulip Beds; it was later described in 2012, by Legg ''et al,'' as a basal hymenocarine, naming the type species ''Neroecaris exilis.'' In 2013, a second ''Nereocaris briggsi'' was described by Legg and Caron. The generic name, ''Nereocaris'' comes from Greek: , Nereus the Greek god of waves; and , "shrimp" or "crab", meaning "Nereus's shrimp". The specific name ''exilis'' comes from Latin, meaning slim; while the second species' name ''briggsi'' means "of Briggs", referring to professor Derek Briggs, an expert on Cambrian arthropods. Description According to the diagnosis of Legg and Caron (2013), the genus including both species is diagnosed by the presence of two ...
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Branchiocaris
''Branchiocaris'' is an extinct genus of Cambrian bivalved arthropod. The type and best known species, ''Branchiocaris pretiosa,'' was described from the Burgess Shale of British Columbia, Canada, in 1929, originally placed in '' Protocaris'', and was placed into its own distinct genus by Briggs in 1976. Several other possible species have been described from Cambrian deposits in China, and it is also possibly known from Cambrian deposits in Utah. ''Branchiocaris pretiosa'' is around in length, with a highly segmented trunk, consisting of at least 44 ring-like segments, terminating in a forked tail telson. At the front of the animal is a pair of short segmented tapered antennules with at least 20 segments, as well as a pair of claw appendages. It was likely an active swimmer, and used the claw appendages to bring food to the mouth. The discovery of ''Tokummia'' from the Burgess Shale, believed to be a close relative of ''Branchiocaris'', has shed light on the evolutionary placem ...
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Arthropods
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arthropod cuticle, cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. Arthropods are bilaterally symmetrical and their body possesses an exoskeleton, external skeleton. 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. Some species have wings. They are an extremely diverse group, with up to 10 million species. The haemocoel, an arthropod's internal cavity, through which its haemolymph – analogue of blood – circulates, accommodates its interior Organ (anatomy), organs; it has an open circulatory system. Like their exteriors, the internal or ...
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Waptia
''Waptia fieldensis'' is an extinct species of arthropod from the Middle Cambrian Burgess Shale ''Lagerstätte'' of Canada. It grew to a length of , and had a large bivalved carapace and a segmented body terminating into a pair of tail flaps. It was an active swimmer and likely a predator of soft-bodied prey. It is also one of the oldest animals with direct evidence of brood care. ''Waptia fieldensis'' is the only species classified under the genus ''Waptia''. Other specimens of ''Waptia'' are known from the Spence Shale in Utah. Based on the number of individuals, ''Waptia fieldensis'' is the third most abundant arthropod from the Burgess Shale Formation, with thousands of specimens collected. It was among the first fossils found by the American paleontologist Charles D. Walcott in 1909. He described it in 1912 and named it after two mountains near the discovery site – Wapta Mountain and Mount Field, other specimens Although it bears a remarkable resemblance to modern c ...
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Plenocaris
''Plenocaris plena'' is a Cambrian arthropod with a bivalved carapace, and is known from the Burgess shale and Chengjiang. Originally described as a species of ''Yohoia'' by Walcott in 1912, it was placed into its own genus in 1974. The head has a pair of simple antennae. The body has 13 tergites, with trunk tergites 2 to 4 having pairs of elongate and uniramous appendages, with appendages absent from the other body segments. The body terminates with paired tail flukes. unlike waptiids, but similar to '' Synophalos,'' the tail flukes lack segmentation. 106 specimens of ''Plenocaris'' are known from the Greater Phyllopod bed, where they comprise 0.20% of the community. It has been suggested to be a member of Hymenocarina Hymenocarina is an order of extinct 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 f ..., which co ...
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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 has pairs of cephalic appen ...
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Canadaspis
''Canadaspis'' ("Shield of Canada") is an extinct genus of bivalved Cambrian arthropod, known from North America and China. They are thought to have been benthic feeders that moved mainly by walking and possibly used its biramous appendages to stir mud in search of food. They have been placed within the Hymenocarina, which includes other bivalved Cambrian arthropods. Description ''Canadaspis'' ''perfecta'' The bivalved carapaces of ''Canadaspis'' ''perfecta'' are typically in length, which taper towards the front end. The head had a small pair of eyes borne on short stalks. Between the eyes is a forward pointing spine, as well as a pair of short antennae, which appear to lack segmentation. Similar antennae are known from '' Waptia'', and are probably homologous to the hemi-ellipsoid bodies of crustaceans, and thus likely have an olfactory function. The head also has another pair of larger, segmented antennae, probably with more than 12 segments, the segments increased in len ...
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Pectocaris
''Pectocaris'' is a genus of extinct bivalved arthropod from the Cambrian Maotianshan Shale, Yunnan Province of China. There are currently three known species within the genus. Discovery The first species in the genus, ''Pectocaris spatiosa'', was described in 1999 from fossils from Maotianshan Shale, however they were not the first fossils of the genus to be dug out of the formation, in 1987 partial hymenocarine fossils were described as belonging to the genus ''Odaraia'' (''Odaraia'' ? ''eurypetala'')''.'' Since these fossils were partially preserved, they were not recognised as part of a different genus until 2004, keeping their species name, erecting ''Pectocaris euryptela.'' The final species, ''Pectocaris inopinata'' was not described until 2021. All species come from the Yu'anshan Member of the Chiungchussu Formation. The genus' name, ''Pectocaris'', comes from Latin ''Pecto'', "comb"; and ''caris'', "shrimp" or "crab". Description and Species ''Pectocaris'' possess ...
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Protocaris
''Protocaris marshi'' is an extinct species of bivalved arthropod known from a single specimen collected from the Cambrian Series 2 aged Parker Formation from the Parker Quarry of northwestern Vermont, United States The specimen is preserved in top-down view and has a bivalved carapace, a segmented trunk and a forked tail. Its precise taxonomic position is uncertain, due to the limited nature of known remains, but it is suggested to be a member of Hymenocarina belonging to the family Protocarididae, which also includes ''Tokummia'' and ''Branchiocaris ''Branchiocaris'' is an extinct genus of Cambrian bivalved arthropod. The type and best known species, ''Branchiocaris pretiosa,'' was described from the Burgess Shale of British Columbia, Canada, in 1929, originally placed in '' Protocaris'', an ....'' References Cambrian arthropods {{branchiopoda-stub Hymenocarina ...
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Ercaicunia
''Ercaicunia'' is genus of bivalved Cambrian arthropod from the Chengjiang biota of Yunnan, China. It contains a single species, ''E. multinodosa'' that was described by Luo et al. in 1999. The total length of the body ranges from . The bivalved carapace covered about a third of the total body-length, and has up to six serrations on its forward edge. The head has a pair of large uniramous antennae, as well as a smaller pair of secondary antennae, as well as pair of mandibles and maxillae. The trunk has 16 pairs of biramous appendages. Specimens were CT scanned in 2019, which suggested it to be a stem-group crustacean. Other subsequent studies have recovered it as a member of Hymenocarina, which contains other bivalved Cambrian arthropods. See also * Arthropod * Cambrian explosion * Chengjiang biota The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional pres ...
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Balhuticaris
''Balhuticaris'' is a genus of extinct bivalved (referring to the carapace) hymenocarine arthropod that lived in the Cambrian aged Burgess Shale in what is now British Columbia around 506 million years ago. This extremely multisegmented (with over 100 segments) arthropod is the largest member of the group, and it was even one of the largest animals of the Cambrian, with individuals reaching lengths of 245 mm (9 in). Fossils of this animal suggests that gigantism occurred in more groups of Arthropoda than had been previously thought. It also presents the possibility that bivalved arthropods were very diverse, and filled in a lot of ecological niches. The hymenocarines were an order of primitive mandibulates, the arthropod group that includes crustaceans, insects, myriapods and their relatives, that lived throughout the Cambrian period. This group was extremely diverse and attained a wide variety of ecological niches and body plans. Several dozen species are known ...
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Fibulacaris
''Fibulacaris'' is a monotypic genus of fossil arthropod known only by one species, ''Fibulacaris nereidis'', discovered from the Cambrian Burgess Shale of Canada It was characterized by a bivalved carapace with an inverted rostrum, sandwiching the slender body with stalked eyes and homonomous appendages. It was probably an actively swimming filter feeder and possibly swam upside-down like some branchiopod crustaceans and horseshoe crabs. Phylogenetic analysis suggest it was a relative or member of Hymenocarina Hymenocarina is an order of extinct 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 f ..., which contains other bivalved arthropods. References Burgess Shale fossils Prehistoric arthropod genera {{Arthropod-stub Cambrian genus extinctions Hymenocarina ...
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