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A chordate is an animal of the phylum Chordata. All chordates possess 5 synapomorphies, or primary characteristics, at some point during their larval or adulthood stages that distinguish them from all other taxa. These 5 synapomorphies include a notochord, dorsal hollow nerve cord, endostyle or thyroid, pharyngeal slits, and a post-anal tail. The name “chordate” comes from the first of these synapomorphies, the notochord, which plays a significant role in chordate structure and movement. Chordates are also bilaterally symmetric, have a coelom, possess a circulatory system, and exhibit metameric segmentation.
Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta, and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs.
Graptolithina is a subclass of the class Pterobranchia, the members of which are known as graptolites. These organisms are colonial animals known chiefly as fossils from the Middle Cambrian through the Lower Carboniferous (Mississippian). A possible early graptolite, Chaunograptus, is known from the Middle Cambrian. One analysis suggests that the pterobranch Rhabdopleura represents extant graptolites. Studies on the tubarium of fossil and living graptolites showed similarities in the basic fusellar construction and it is considered that the group most probably evolved from a Rhabdopleura-like ancestor.
Haikouella is an agnathan chordate from the Lower Cambrian Maotianshan shales of Chengjiang County in Yunnan Province, China.
Pterobranchia is a class of small worm-shaped animals. They belong to the Hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water with the help of cilia attached to tentacles. There are about 25 known living pterobranch species in three genera, which are Rhabdopleura, Cephalodiscus, and Atubaria. On the other hand, there are several hundred extinct genera, some of which date from the Cambrian Period.
The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in the world, the main species for research being Saccoglossus kowalevskii. Two families—Harrimaniidae and Ptychoderidae—separated at least 370 million years ago.
Margaretia is a frondose organism known from the middle Cambrian Burgess shale and the Kinzers Formation of Pennsylvania. Its fronds reached about 10 cm in length and are peppered with a range of length-parallel oval holes. It was originally interpreted as an alcyonarian coral. It was later reclassified as a green alga closely resembling modern Caulerpa by D.F. Satterthwait in her Ph.D. thesis in 1976, a finding supported by Conway Morris and Robison in 1988. More recently, it has been treated as an organic tube, that is used as nest of hemichordate Oesia.
The Wheeler Shale is a Cambrian (c. 507 Ma) fossil locality world-famous for prolific agnostid and Elrathia kingii trilobite remains and represents a Konzentrat-Lagerstätte. Varied soft bodied organisms are locally preserved, a fauna and preservation style normally associated with the more famous Burgess Shale. As such, the Wheeler Shale also represents a Konservat-Lagerstätten.
Deuterostomia are animals typically characterized by their anus forming before their mouth during embryonic development. The group's sister clade is Protostomia, animals whose digestive tract development is more varied. Some examples of deuterostomes include vertebrates, sea stars, and crinoids.
In evolutionary developmental biology, inversion refers to the hypothesis that during the course of animal evolution, the structures along the dorsoventral (DV) axis have taken on an orientation opposite that of the ancestral form.
Cephalodiscida is one of two orders in the class Pterobranchia, which are small, worm-shaped animals. Members belong to the hemichordates. Species in this order are sessile, living in clear water and secrete tubes on the ocean floor.
Rhabdopleurida is one of three orders in the class Pterobranchia, which are small, worm-shaped animals, are the only surviving graptolites. Members belong to the hemichordates. Species in this order are sessile, colonial, connected with a stolon, living in clear water and secrete tubes called tubarium. They have a single gonad, the gill slits are absent and the collar has two tentaculated arms. Rhabdopleura is the best studied pterobranch in developmental biology. Rhabdopleura is the only extant graptolite.
Rhabdopleura is a genus of colonial sessile hemichordates belonging to the Pterobranchia class. As one of the oldest living genera with a fossil record dating back to the Middle Cambrian, it is also considered to be the only living genus of graptolites.
Rhabdopleura normani is a small, marine species of worm-shaped animal known as a pterobranch. It is a sessile suspension feeder, lives in clear water, and secretes tubes on the ocean floor.
Mawia is a genus of jellyfish in the family Pelagiidae. It is a monotypic genus with the sole species Mawia benovici. The team who discovered this jellyfish named it benovici after a late colleague, Adam Benovic. Although described based on specimens from the Adriatic Sea, a part of the Mediterranean, it was speculated that these might be transplants rather than a part of its natural range. A later study found specimens in Senegal, indicating that its natural range possibly is the Atlantic Ocean off West Africa.
Neodermata is a clade of rhabditophoran flatworms containing the parasitic groups Trematoda, Monogenea and Cestoda.
Cephalodiscus is a genus of hemichordates in the monotypic family Cephalodiscidae of the order Cephalodiscida.
Rhabdopleura annulata is a sessile hemichordate. It is a suspension feeder that secretes tubes on the ocean floor.
Rhabdopleura compacta is a sessile hemichordate. It is a suspension feeder that secretes tubes on the ocean floor.
Rhabdopleura striata is a sessile hemichordate. It is a suspension feeder that secretes tubes on the ocean floor.
References
- ↑ Strano, F.; Micaroni, V.; Beli, E.; Mercurio, S.; Scarì, G.; Pennati, R.; Piraino, S. (7 January 2019). "On the larva and the zooid of the pterobranch Rhabdopleura recondita Beli, Cameron and Piraino, 2018 (Hemichordata, Graptolithina)" (PDF). Marine Biodiversity. 49 (4): 1657–1666. doi:10.1007/s12526-018-0933-2. ISSN 1867-1616.
- 1 2 Beli, Elena; Aglieri, Giorgio; Strano, Francesca; Maggioni, Davide; Telford, Max J.; Piraino, Stefano; Cameron, Christopher B. (2018). "The zoogeography of extant rhabdopleurid hemichordates (Pterobranchia: Graptolithina), with a new species from the Mediterranean Sea" (PDF). Invertebrate Systematics. 32 (1): 100. doi:10.1071/is17021. ISSN 1445-5226.
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