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Lancelets
The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochordata. Lancelets closely resemble 530-million-year-old ''Pikaia'', fossils of which are known from the Burgess Shale. 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 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 fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chordates
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five 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. In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in their proteins: cyclophilin-like protein and mitochondrial inner membrane protease ATP23, which are exclusively shared by all vertebrates, tunicates and cephalochordates. These CSIs prov ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalochordata
A cephalochordate (from Greek language, Greek: κεφαλή ''kephalé'', "head" and χορδή ''khordé'', "chord") is an animal in the chordate subphylum, Cephalochordata. They are commonly called Lancelet, lancelets. Cephalochordates possess 5 synapomorphies, or primary characteristics, that all chordates have at some point during their larval or adulthood stages. These 5 synapomorphies include a notochord, dorsal hollow nerve cord, endostyle, Pharyngeal slit, pharyngeal slits, and a post-anal tail (see chordate for descriptions of each). 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 commun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branchiostoma
''Branchiostoma'' is one of the few living genera of lancelets ( order Amphioxiformes). It is the type genus of family Branchiostomatidae. These small vaguely eel- or snake-like animals are close relatives of vertebrates. The scientific name means "gill-mouth", referring to their anatomy – unlike vertebrates, they do not have a true head (with a skull capsule, eyes, nose, a well-developed brain etc.), but merely a mouth adjacent to the gill-slits, with the slightly enlarged anterior end of the dorsal nerve cord above and in front of them. It dislikes the light. Like all lancelets, they are filter feeders that hide in the sediment most of the time. The genus inhabits coastal waters throughout the world. Species * '' Branchiostoma africae'' Hubbs, 1927 * '' Branchiostoma arabiae'' Webb, 1957 * '' Branchiostoma bazarutense'' Gilchrist, 1923 * '' Branchiostoma belcheri'' Gray, 1847 (Belcher's lancelet) * ''Branchiostoma bennetti'' Boschung & Gunter, 1966 (Mud lancelet) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pikaia
''Pikaia gracilens'' is an extinct, 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 the "most famous early chordate fossil," or "famously known as the earliest" chordates. It is estimated to have lived during the latter period of the Cambrian explosion. Since it initial discovery, more than a hundred specimens have been recovered. The body structure resembles that of the lancelet and perhaps it swam much like an eel. A notochord and myomeres (segmented blocks of skeletal muscles) span the entire length of the body, and are considered as the defining signatures of chordate characters. Its primitive feature is indicated by the body covering, a cuticle, which is characteristic of invertebrates and some protochordates. The exact phylogenetic position is unclear. Proposed affinities include ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hagfish
Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, although hagfish do have rudimentary vertebrae. Along with lampreys, hagfish are jawless; the two form the sister group to jawed vertebrates, and living hagfish remain similar to hagfish from around 300 million years ago. The classification of hagfish had been controversial. The issue was whether the hagfish was a degenerate type of vertebrate-fish that through evolution had lost its vertebrae (the original scheme) and was most closely related to lampreys, or whether hagfish represent a stage that precedes the evolution of the vertebral column (the alternative scheme) as is the case with lancelets. Recent DNA evidence has supported the original scheme. The original scheme groups hagfish and lampreys together as cyclostomes (or historicall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branchiostomatidae
Branchiostomatidae is a family of lancelets The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochord ... belonging to the class Leptocardii, order unknown. Genera: * ''Asymmetron'' Andrews, 1893 * ''Branchiostoma'' Costa, 1834 * ''Epigonichthys'' Peters, 1876 * ''Epigonopterus'' Jordan & Gilbert, 1882 * †''Palaeobranchiostoma'' Oelofsen & Loock, 1981 References {{Taxonbar, from1=Q2747865, from2=Q61882392 Cephalochordata ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asymmetronidae
''Asymmetron'' is a genus of lancelets belonging to the family Branchiostomatidae. The species of this genus are found in world oceans. Species: *''Asymmetron inferum'' *''Asymmetron lucayanum ''Asymmetron'' is a genus of lancelets belonging to the family Branchiostomatidae Branchiostomatidae is a family of lancelets belonging to the class Leptocardii, order unknown. Genera: * ''Asymmetron'' Andrews, 1893 * '' Branchiostoma'' Costa, ...'' References {{Taxonbar, from=Q9635660 Cephalochordata ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Vertebrates comprise such groups as the following: * jawless fish, which include hagfish and lampreys * jawed vertebrates, which include: ** cartilaginous fish (sharks, rays, and ratfish) ** bony vertebrates, which include: *** ray-fins (the majority of living bony fish) *** lobe-fins, which include: **** coelacanths and lungfish **** tetrapods (limbed vertebrates) Extant vertebrates range in size from the frog species ''Paedophryne amauensis'', at as little as , to the blue whale, at up to . Vertebrates make up less than five percent of all described animal species; the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do no ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fertilisation
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally called fertilisation. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation. History In Antiquity, Aristotle conceived the formation of new individuals through fusion of male and female fluids, with form and function emerging gradually, in a mode called by him as epigenetic. In 1784, Spallanzani established the need of interaction between the female's ovum and male's sperm to form a zygote in frog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spawn (biology)
Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquatic mammals and marine reptile, reptiles, reproduce through the process of spawning. Spawn consists of the reproductive cells (gametes) of many aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing Ovum, ova (unfertilized eggs) into the water, often in large quantities, while males simultaneously or sequentially release spermatozoa (milt) to fertilize the eggs. Most fish reproduce by spawning, as do most other aquatic animals, including crustaceans such as crabs and shrimps, molluscs such as oysters and squid, echinoderms such as sea urchins and sea cucumbers, amphibians such as frogs and newts, aquatic insects such as mayflies and mos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linda Holland
Linda Zimmerman Holland is a research biologist at Scripps Institution of Oceanography known for her work examining the evolution of vertebrates. Education and career Holland has a B.A. (1962) and an M.A. (1964) from Stanford University. She worked as a research associate at the University of California, San Diego, Scripps Clinic, and Scripps Institution of Oceanography in the period from 1970 until 1998. She earned her Ph.D. from the University of California, San Diego in 2001. She started as a research biologist at Scripps in 1998, and is emeritus as of 2022. Linda Holland has described in detail some of the early obstacles she faced as a woman scientist starting out in academe in the 1960s and 1970s, Research Holland's early research examined anatomical structures in purple sea urchins, and a protein involved in clotting, Von Willebrand factor. She went on to examine reproduction in sea urchins, salps, and amphioxus, known as lancelet. Holland began collecting amphioxus in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peter Simon Pallas
Peter Simon Pallas Fellow of the Royal Society, FRS FRSE (22 September 1741 – 8 September 1811) was a Prussian zoologist and botanist who worked in Russia between 1767 and 1810. Life and work Peter Simon Pallas was born in Berlin, the son of Professor of Surgery Simon Pallas. He studied with private tutors and took an interest in natural history, later attending the University of Halle and the University of Göttingen. In 1760, he moved to the University of Leiden and passed his doctor's degree at the age of 19. Pallas travelled throughout the Netherlands and to London, improving his medical and surgical knowledge. He then settled at The Hague, and his new system of animal classification was praised by Georges Cuvier. Pallas wrote ''Miscellanea Zoologica'' (1766), which included descriptions of several vertebrates new to science which he had discovered in the Dutch museum collections. A planned voyage to southern Africa and the East Indies fell through when his father reca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
