A chordate is a deuterostomic animal belonging to the phylum Chordata. All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa. These five synapomorphies are a notochord, a hollow dorsal nerve cord, an 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 body plan structuring and movements. Chordates are also bilaterally symmetric, have a coelom, possess a closed circulatory system, and exhibit metameric segmentation.
In zoology and developmental anatomy, the notochord is an elastic rod-like structure found in many deuterostomal animals. Any species that has a notochord at any stage of its life cycle is, by definition, a chordate.
Pikaia gracilens is an extinct species of primitive chordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Simon Conway Morris as a chordate, it became "one of the most famous early chordate fossils," or "famously known as the earliest described Cambrian chordate". It is estimated to have lived during the latter period of the Cambrian explosion. Since its initial discovery, more than a hundred specimens have been recovered.
A cephalochordate is an animal in the chordate subphylum Cephalochordata. Cephalochordates are commonly called lancelets, and possess 5 synapomorphies, or primary characteristics, that all chordates have at some point during their larval or adulthood stages. These 5 synapomorphies are a notochord, dorsal hollow nerve cord, endostyle, pharyngeal slits, and a post-anal tail. The fine structure of the cephalochordate notochord is best known for the Bahamas lancelet, Asymmetron lucayanum. Cephalochordates are represented in modern oceans by the Amphioxiformes and are commonly found in warm temperate and tropical seas worldwide. With the presence of a notochord, adult amphioxus are able to swim and tolerate the tides of coastal environments, but they are most likely to be found within the sediment of these communities.
The lancelets, also known as amphioxi, consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are modern representatives of the subphylum Cephalochordata. Lancelets closely resemble 530-million-year-old Pikaia, fossils of which are known from the Burgess Shale. However, according to phylogenetic analysis, the lancelet group itself probably evolved around the Cretaceous, 97.7 million years ago for Pacific species and 112 million years ago for Atlantic species. Palaeobranchiostoma from the Permian may be part of the fossil record of lancelets; however, due to poor preservation, some doubt about its nature remains. Zoologists are interested in them because they provide evolutionary insight into the origins of vertebrates. Lancelets contain many organs and organ systems that are closely related to those of modern fish, but in a more primitive form. Therefore, they provide a number of examples of possible evolutionary exaptation. For example, the gill-slits of lancelets are used for feeding only, and not for respiration. The circulatory system carries food throughout their body, but does not have red blood cells or hemoglobin for transporting oxygen. Lancelet genomes hold clues about the early evolution of vertebrates: by comparing genes from lancelets with the same genes in vertebrates, changes in gene expression, function and number as vertebrates evolved can be discovered. The genome of a few species in the genus Branchiostoma have been sequenced: B. floridae,B. belcheri, and B. lanceolatum.
The ParaHox gene cluster is an array of homeobox genes from the Gsx, Xlox (Pdx) and Cdx gene families.
Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body. For example, Hox genes in insects specify which appendages form on a segment, and Hox genes in vertebrates specify the types and shape of vertebrae that will form. In segmented animals, Hox proteins thus confer segmental or positional identity, but do not form the actual segments themselves.
The recombination-activating genes (RAGs) encode parts of a protein complex that plays important roles in the rearrangement and recombination of the genes encoding immunoglobulin and T cell receptor molecules. There are two recombination-activating genes RAG1 and RAG2, whose cellular expression is restricted to lymphocytes during their developmental stages. The enzymes encoded by these genes, RAG-1 and RAG-2, are essential to the generation of mature B cells and T cells, two types of lymphocyte that are crucial components of the adaptive immune system.
Strongylocentrotus purpuratus, the purple sea urchin, lives along the eastern edge of the Pacific Ocean extending from Ensenada, Mexico, to British Columbia, Canada. This sea urchin species is deep purple in color, and lives in lower inter-tidal and nearshore sub-tidal communities. Its eggs are orange when secreted in water. January, February, and March function as the typical active reproductive months for the species. Sexual maturity is reached around two years. It normally grows to a diameter of about 10 cm (4 inches) and may live as long as 70 years.
The 2R hypothesis or Ohno's hypothesis, first proposed by Susumu Ohno in 1970, is a hypothesis that the genomes of the early vertebrate lineage underwent two complete genome duplications, and thus modern vertebrate genomes reflect paleopolyploidy. The name derives from the 2 rounds of duplication originally hypothesized by Ohno, but refined in a 1994 version, and the term 2R hypothesis was probably coined in 1999. Variations in the number and timings of genome duplications typically still are referred to as examples of the 2R hypothesis.
Chordate genomics is the study of the evolution of the chordate clade based on a comparison of the genomes of several species within the clade. The field depends on whole genome data of organisms. It uses comparisons of synteny blocks, chromosome translocation, and other genomic rearrangements to determine the evolutionary history of the clade, and to reconstruct the genome of the founding species.
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.
Branchiostoma floridae, the Florida lancelet, is a lancelet of the genus Branchiostoma. The genome of this species has been sequenced, revealing that among the chordates, the morphologically simpler tunicates are actually more closely related to vertebrates than lancelets. An embryo of a Florida amphioxus has a larval pharynx with gill slits that is asymmetrical. The gill slits in the larval pharynx form in the center of the embryo when it is in its earliest stage of development (primordial) meaning the thick layer of endoderm is overlapped by a thin layer; which aids into making the B. floridae asymmetrical from left to right. The lancelet Branchiostoma floridae maintains a high level of Fox transcription factor gene diversity, with 32 distinct Fox genes in its genome, and 21,229 clusters of cDNA clones, making it very useful to the research community.
Branchiostoma lanceolatum, the European lancelet or Mediterranean amphioxus, is a lancelet in the subphylum Cephalochordata. It is a marine invertebrate with a notochord but no backbone and is used as a model organism to study the evolutionary development of vertebrates.
Hepatic caecum or hepatic cecum is a name used in describing various physiological structures in some crustaceans, insects and lancelets. "Hepatic" refers to the liver, and the hepatic caecum may perform some functions that are analogous to the functions of the liver in vertebrates.
In biology, solenocytes are elongated, flagellated cells commonly found in lower invertebrates, such as flatworms, as well as in chordates and several other animal species. In terms of function, solenocytes play a significant role in the excretory systems of their host organism(s). For example, the lancelets, also referred to as amphioxus, utilize solenocytic protonephridia to perform excretion. In addition to excretion, these cells contribute to ion regulation and osmoregulation. With this in mind, solenocytes form subtypes of protonephridium and are often compared to another specialized excretory cell type, i.e., flame cells. Solenocytes have flagella, while flame cells are generally ciliated.
Transib is a superfamily of interspersed repeats DNA transposons. It was named after the Trans-Siberian Express. It is similar to EnSpm/CACTA.
Cytochrome P450, family 11, also known as CYP11, is a chordate cytochrome P450 monooxygenase family. This family contains many enzymes involved in steroidogenesis, such as Cholesterol side-chain cleavage enzyme (CYP11A1), Steroid 11β-hydroxylase (CYP11B1) and Aldosterone synthase (CYP11B2). CYP11 can be divided into A to E five subfamilies, and CYP11A are the ohonologues to CYP11C, which duplicated during 2R event, and the tetrapod's CYP11B evolved from CYP11C of its fish ancestors, CYP11D and F found in amphioxus. These are not the typical CYP subfamilies, which share at least 40% amino acid identity, members between CYP11A and B subfamily are only 37.5-38.8% identical, and the CYP11D and E genes seen in modern lancelet is 39% identical to catfish CYP11A1.
Amphioxus or lancelets (Branchiostoma) are members of the Chordata phylum of which all members have a notochord at some point while they are alive. B. belcheri have a notochord, dorsal nerve cord, pharynx, buccal cavity, cirri, tail, dorsal fin, nerve cord, segmented muscle, and ocelli. They are distinguishable by a slightly round dorsal fin, eighty slender preanal fin-chambers, narrow caudal fin, and obtuse angles between fins. They obtain food by filter feeding. They were first reported in 1897 near the Amakusa Islands, specifically off Goshonoura Island, south of Amakusa-Kamishima Island. These islands are located on the west coast of Kyushu, the island furthest south of the four main isles of Japan. In addition to the location of the siting, information regarding reproductive period and morphology was also obtained. B. belcheri are gonochoric, reproducing via external fertilization. B. belcheri are an endangered species, threatened by the influx of pollutants of land-based origin into the sea such as cleaning agents, chemical waste, garbage, mining waste, pesticides, petroleum products, and sewage.
