Sidneyia is an extinct arthropod known from fossils found from the Early to the Mid Cambrian of China and the Mid Cambrian Burgess Shale of British Columbia, Canada.
Canadaspis 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.
Waptia is an extinct genus of arthropod from the Middle Cambrian of North America. It grew to a length of 6.65 cm (3 in), 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, and is known from the Burgess Shale Lagerstätte of British Columbia, Canada. Specimens of Waptia are also known from the Spence Shale of Utah, United States.
Habelia is a genus of extinct arthropod from the Middle Cambrian, thought to be one of the earliest known relatives of chelicerates. Its fossils have been found in the Burgess Shale in British Columbia, Canada. Fifty-four specimens of Habelia are known from the Greater Phyllopod bed, where they comprise 0.1% of the community.
Megacheira 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 to middle Cambrian.
Tuzoia 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 180 millimetres (7.1 in), making them amongst the largest known Cambrian arthropods.
Chuandianella ovata is an extinct bivalved arthropod that lived during Cambrian Stage 3 of the Early Cambrian. It is the only species classified under the genus Chuandianella. Its fossils were recovered from the Chengjiang Biota in Yunnan, China.
Isoxys 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, and two large frontal appendages used to grasp prey.
Pectocaris is an extinct genus of bivalved arthropods from the Cambrian Maotianshan Shales, Yunnan Province of China. There are currently three known species within the genus.
Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two originally refer to the family Anomalocarididae, which previously included all species of this order but is now restricted to only a few species. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and used for a variety of functions. Radiodonts included the earliest large predators known, 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 gainessii, Cambroraster falcatus and Amplectobelua symbrachiata, the Ordovician Aegirocassis benmoulai and the Devonian Schinderhannes bartelsi.
Bradoriida, also called bradoriids, are an extinct order of small marine arthropods with a bivalved carapace, which globally distributed, forming a significant portion of the Cambrian and Early Ordovician soft-bodied communities.
Kootenichela deppi is an extinct arthropod described from the Middle Cambrian of the Kootenay National Park, Canada. It is originally considered to be a member of "great appendage arthropods", although subsequent studies questioned its affinity. Kootenichela appears to be the sister taxon of Worthenella, from cladistic analysis.
Retifacies abnormalis is an extinct arthropod that lived in the lower Cambrian. Its fossil remains have been found in the Maotianshan Shales of Yunnan, China. It is a member of the Artiopoda, and closely related to Pygmaclypeatus.
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 to the presence of mandibles in some species.
Kylinxia is a genus of extinct arthropod described in 2020. It was described from six specimens discovered in Yu'anshan Formation in southern China. The specimens are assigned to one species Kylinxia zhangi. Dated to 518 million years, the fossils falls under the Cambrian period. Announcing the discovery on 4 November 2020 at a press conference, Zeng Han of the Nanjing Institute of Geology and Paleontology, said that the animal "bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key ‘missing link’ in the origin of arthropods," which was "predicted by Darwin’s evolutionary theory." The same day the formal description was published in Nature.
Erratus is an extinct genus of marine arthropod from the Cambrian of China. Its type and only species is Erratus sperare. Erratus is likely one of the most basal known arthropods, and its discovery has helped scientists understand the early evolution of arthropod trunk appendages. Some of the stem-arthropods like radiodonts did not have legs, instead they had flap like appendages that helped them swim. Erratus on the other hand had not only flaps but also a set of primitive legs. It also supported the theory that the gills of aquatic arthropods probably evolved into the wings and lungs of terrestrial arthropods later in the Paleozoic.
Balhuticaris is a genus of extinct bivalved hymenocarine arthropod that lived in the Cambrian aged Burgess Shale in what is now British Columbia around 506 million years ago. This extremely multisegmented 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.
Jugatacaris is an extinct genus of bivalved arthropod known from a single species, Jugatacaris agilis found in the Cambrian Stage 3 aged Chengjiang biota of Yunnan, China. The carapace is around 28 to 37 millimetres in length, with a pronounced ridge at the top of the carapace separating the two valves, which formed a fin-like structure raised above the carapace. The head has a pair of stalked eyes, as well as a dumbbell shaped medial eye between them. The head also bore a pair of mandibles as well as at least one and possibly two pairs of antennules. The trunk had up to 65 segments, each with biramous appendages. The appendages had thin endopods with 30 podomeres, each bearing a spiny endite, with the endopods ending with a terminal claw. The appendages also had overlapping flap-like exopods, which are elongated, being at maximum eight times as long as they are wide, which on their posterior edge are covered with setae. The trunk ended with a forked tail. It was likely an actively swimming filter feeder, using its constantly beating appendages to sift food from the water column, which was then passed forward along the U-shaped food groove between the appendage pairs towards the mouth. While initially placed as a crustaceanomorph, later studies considered to be a member of Hymenocarina, which contains numerous other similar bivalved Cambrian arthropods.
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.
Carimersa is an extinct genus of artiopodan arthropod known from the Silurian Coalbrookdale Formation of Herefordshire, England.
