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There are soft constraints that separate chordates from other biological lineages, but are not part of the formal definition: All chordates are deuterostomes . This means that, during embryonic development , the anus forms before the mouth does.
- Anatomy
- Classification
- Subphyla
- Phylogeny
- Closest Nonchordate relatives
- History of Name
- See Also
Chordates form a phylumof animals that are defined by having at some stage in their lives all of the following anatomical features: 1. A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal...
The following schema is from the 2015 edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships (similar to a cladogram), it also retains the traditional ranks used in Linnaean taxonomy. 1. Phylum Chordata 1.1. Subphylum Cephalochordata (Ac...
Cephalochordata: Lancelets
Cephalochordates, one of the three subdivisions of chordates, are small, "vaguely fish-shaped" animals that lack brains, clearly defined heads and specialized sense organs.These burrowing filter-feeders compose the earliest-branching chordate sub-phylum.
Tunicata
Most tunicates appear as adults in two major forms, known as "sea squirts" and salps, both of which are soft-bodied filter-feeders that lack the standard features of chordates. Sea squirts are sessile and consist mainly of water pumps and filter-feeding apparatus; salps float in mid-water, feeding on plankton, and have a two-generation cycle in which one generation is solitary and the next forms chain-like colonies. However, all tunicate larvae have the standard chordate features, including l...
Craniata
Craniates all have distinct skulls. They include the hagfish, which have no vertebrae. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or possibly all deuterostomes, are by their tails". Most craniates are vertebrates, in which the notochord is replaced by the vertebral column. These consist of a series of bony or cartilaginous cylindrical vertebrae, generally with neural arches that protect the spinal cord, and with projections that link the v...
Overview
There is still much ongoing differential (DNA sequence based) comparison research that is trying to separate out the simplest forms of chordates. As some lineages of the 90% of species that lack a backbone or notochord might have lost these structures over time, this complicates the classification of chordates. Some chordate lineages may only be found by DNA analysis, when there is no physical trace of any chordate-like structures. Attempts to work out the evolutionary relationships of the ch...
Cladogram
Phylogenetic tree of the chordate phylum. Lines of the cladogram show probable evolutionary relationships between both extinct taxa, which are denoted with a dagger (†), and extant taxa. Relatives of vertebrates are invertebrates. The positions (relationships) of the lancelets, tunicates, and craniates/vertebrates are based on the following studies: Amphioxiformes(lancelets) †Haikouella Appendicularia (formerly Larvacea) "Ascidiacea" (polyphyletic; sea squirts) Thaliacea (salps) Myxini (hagfi...
The closest relatives of the Chordates are the Hemichordates and Echinodermata, which together form the Ambulacraria. The Chordata and Ambulacraria together form the superphylum Deuterostomia.
Although the name Chordata is attributed to William Bateson (1885), it was already in prevalent use by 1880. Ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN codebecause of its subsequent latinization.
Identify the derived character of craniates that sets them apart from other chordates; Describe the developmental fate of the notochord in vertebrates
Protochordata (or Acraniata) are separated from the Vertebrata (or Craniata) that have a skull. Vertebrates may be divided into Agnatha (jawless) and Gnathostomata (having jaws). Vertebrates are also divided into Amniota, having an amnion, and Anamniota lacking an amnion.
Identify the derived characters of craniates that sets them apart from other chordates; Describe the developmental fate of the notochord in vertebrates
Sep 11, 2024 · Theories that derive them from other phyla (e.g., Annelida, Nemertea, Arthropoda) have been proposed, but such theories have few contemporary advocates. Whether the first ancestral chordate was more like a tunicate or a cephalochordate has been extensively debated.
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Apr 7, 2019 · There are three subphyla to Chordata: Cepahlochordata, Urochordata, and Vertebrata. Chordates generally have bilaterally symmetric bodies, though a few exceptions exist, and they share distinct characteristics that will be discussed later on. Characteristics of Chordates.
