Recall that animals that possess bilateral symmetry can be divided into two The deuterostome phylogenetic tree includes Echinodermata and chordata. In this lesson, you will explore a group of organisms known as chordates. You'll learn about their general features and also examine what type of symmetry they. A chordate is an animal belonging to the phylum Chordata; chordates possess a notochord, Attempts to work out the evolutionary relationships of the chordates have fossil record of early chordates is poor, only molecular phylogenetics offers a All chordates are coelomates, and have a fluid filled body cavity called a.
The group contains only about 20 species of sand-burrowing marine creatures. The Cambrian fossils Yunnanozoon and Pikaia are likely related to modern cephalochordates. During the Ordovician Period - Ma jawless or agnathan fishes appeared and diversified. These are the earliest known members of Vertebrata, the chordate subgroup that is most familiar to us. Fossils representing most major lineages of fish-like vertebrates and the earliest tetrapods Amphibia were in existence before the end of the Devonian Period Ma.
Reptile-like tetrapods originated during the Carboniferous - Mamammals differentiated before the end of the Triassic Ma and birds before the end of the Jurassic Ma. The smallest chordates e. Characteristics The notochord is an elongate, rod-like, skeletal structure dorsal to the gut tube and ventral to the nerve cord. The notochord should not be confused with the backbone or vertebral column of most adult vertebrates.
The notochord appears early in embryogeny and plays an important role in promoting or organizing the embryonic development of nearby structures. In most adult chordates the notochord disappears or becomes highly modified. In some non-vertebrate chordates and fishes the notochord persists as a laterally flexible but incompressible skeletal rod that prevents telescopic collapse of the body during swimming.
The nerve cord of chordates develops dorsally in the body as a hollow tube above the notochord. In most species it differentiates in embryogeny into the brain anteriorly and spinal cord that runs through the trunk and tail. Together the brain and spinal cord are the central nervous system to which peripheral sensory and motor nerves connect.
The visceral also called pharyngeal or gill clefts and arches are located in the pharyngeal part of the digestive tract behind the oral cavity and anterior to the esophagus. The visceral clefts appear as several pairs of pouches that push outward from the lateral walls of the pharynx eventually to reach the surface to form the clefts. Thus the clefts are continuous, slit-like passages connecting the pharynx to the exterior.Animals
The soft and skeletal tissues between adjacent clefts are the visceral arches. The embryonic fate of the clefts and slits varies greatly depending on the taxonomic subgroup.
In many of the non-vertebrate chordates, such as tunicates and cephalochordates, the clefts and arches are elaborated as straining devices concerned with capture of small food particles from water. Therefore, the deuterostome ancestor would have been a benthic worm with gill cartilages, a mouth, and the ability to filter feed.
Cephalochordates may have lost their mouth and evolved a velum, while vertebrates lost the ability to filter feed. We next show evidence that invertebrate deuterostome cartilage is acellular, with an ECM of collagen and proteoglycans. Worms were dug with shovels and transported back to the laboratory in ml falcon tubes filled with seawater. Sites in which to dig for the worms were recognized by small circular fecal casts that the animals deposit on the surface of the mud.
Seven-micrometer sections were made on a Spencer microtome and mounted on gelatin-subbed slides. Photographs were taken using Cool Snap Version 1. This monoclonal antibody is specific for vertebrate type II collagen, has a broad species specificity, and does not cross-react with vertebrate nonfibrillar collagens Linsenmayer and Hendrix Collagen Phylogenetic analysis All known Homo sapiens fibrillar collagen amino acid sequences were downloaded from GenBank, and they have the following accession numbers: Invertebrate accession numbers are as follows for all known fibrillar collagens in GenBank— AAC Tunicate fibrillar collagen sequences were downloaded from the Ciona genome Web site http: The mosquito Anopheles gambiae and bee Apis mellifera fibrillar collagen sequences were found via Blast on the Ensembl genome Web site http: For all collagen sequences found via Blast, only those having a triple helical sequence in the same gene or genomic vicinity of a highly conserved noncollagenous domain known to be present in all fibrillar collagens were used.
Chordate - Wikipedia
Amino acid sequences were trimmed to include only the major triple helix, which in complete sequences varied from to 1, amino acids with the majority being in the 1,—1, amino acid range. Each sequence in the data set is represented by a complete major helical domain except for the polychaete, hemichordate, and lancelet sequences.
Because only the C-terminal ends of these sequences were available, an unknown sequence of the appropriate length was added to the N-terminus of these sequences to aid in proper alignment. These amino acid sequences were then aligned using the program ClustalX Jeanmougin et al.
To assess levels of clade support in this analysis, bootstrap support was calculated using 1, pseudoreplicates. Clades with values of 70 and greater were considered well supported Hillis and Bull The data set was further analyzed using Bayesian methods MrBayes v3. Bayesian methods were used to compute tree topologies based on a mixed model of amino acid substitution and allowing for invariant sites and rate heterogeneity among sites gamma parameter.
The analysis was run for 1, generations, and the first 15, trees were discarded as burn-in after the distribution was graphed to ensure that only the trees on the plateau were included. Clades with posterior probabilities 95 and greater were considered strongly supported because they are true probabilities of clades under the assumed models Rannala and Yang Results and Discussion Hemichordates are tricoelomic, with an anterior proboscis, a middle neck region, and a posterior abdomen fig.
The abdomen contains a number of gill slits, which are shown in figure 3A and C. In the harrimaniids, the reported range of gill slits is between 30 andalthough the exact number will vary even within species Smith et al. If the worm is dissected, it is clear that there is an anterior cartilaginous proboscis skeleton and cartilaginous gill bars that support the gill pores fig.
These gill bars have been shown to stain with alcian blue Smith et al. Hermaphroditism possessing both male and female reproductive organs is found in tunicates and some fishes, but otherwise the sexes are separate. Larvae very young forms that differ considerably from the juveniles and adultswhen they do occur, differ in structure from the larvae of nonchordates.
Internal fertilization, viviparity giving birth to young that have undergone embryological developmentand parental care are common in tunicates and vertebrates. Ecology and habitats Chordates are common in all major habitats. Tunicate larvae either seek out a place where they can attach and metamorphose into an adult or develop into adults that float in the open water.
Cephalochordates develop in the open water, but as adults they lie partially or entirely buried in sand and gravel. In either case, they are filter feeders with simple behaviour.
chordate | Definition, Characteristics, & Facts | misjon.info
Vertebrates are much more complex and, in keeping with their more active manner of obtaining food, highly varied in their ecology and habits. Locomotion Chordates are capable of locomotion by means of muscular movements at some stage in life. In tunicate larvae, this is accomplished using a tail; in cephalochordates, by undulations of the body; and in vertebrates, by general body movements as in eels and snakes and by the action of fins and limbs, which in birds and some mammals are modified into wings.
Associations Chordates enter into a wide variety of symbiotic relationships and are especially noteworthy as hosts for parasites. Family groups and societal relationships, in both a broad and narrow sense, are particularly well developed in vertebrates, due primarily to their elaborate nervous systems.
This phenomenon is seen in schools of fish, flocks of birds, and herds of mammals, as well as in the primate associations that suggest the beginnings of human society. Form and function General features Chordates have many distinctive features, suggesting that there has been extensive modification from simple beginnings.
The early stages of chordate development show features shared with some invertebrate phyla, especially the mouth that forms separately from the anus, as it does in the phyla HemichordataEchinodermataand Chaetognatha. Likewise, as in these phyla, the coelomor secondary body cavity around the viscera, develops as outpouchings of the gut. A coelom also is present in some more distantly related phyla, including AnnelidaArthropodaand Molluscabut the main organs of the body are arranged differently in these phyla.
In chordates the main nerve cord is single and lies above the alimentary tractwhile in other phyla it is paired and lies below the gut. Cephalochordates and vertebrates are segmented, as are the annelids and their relatives; however, segmentation in the two groups probably evolved independently. The gill slits and some other features that are common among the hemichordates and the chordates originated before the chordates became a separate group.
Hemichordates have no tail above the gut and no mucus-secreting endostyle between the gill slits. External features An ancestral chordate, as suggested by the adult lancelet and the tadpole larva of tunicates, had a distinct front and hind end, an anterior mouth, a posterior tail above an anus, unpaired fins, and gill slits that opened directly to the exterior. A free-swimming tunicate larva metamorphoses into an attached, sessile adult with an atrium that surrounds the gills.
The atrium of lancelets probably evolved independently. Internal features Skeleton and support The chordate notochord is a stiff rod with a turgid core and fibrous sheath.
It keeps the animal from shortening when locomotory waves are produced through muscular contraction. The chordate body is supported by fluid in the body cavities. In tunicates, added support is provided by the tunic.
Cartilaginous material supports the gills and other body parts of tunicates and cephalochordates. Immature vertebrate skeletons generally consist largely of cartilagewhich becomes increasingly bony with age. The cartilaginous skeletons of sharks and some other vertebrates are thought to have evolved from more highly mineralized ones. Tissues and muscles In both cephalochordates and vertebrates, muscles used in locomotion are well developed and organized segmentally.
The tail musculature of tunicates is simpler and without clear indications of segmentation. There is at least a small amount of musculature throughout the body of all chordates. As jaws, limbs, and other body parts have evolved in vertebrates, so have the muscles that operate them. Nervous system and sense organs The anterior end of the main nerve cord in chordates is enlarged to form at least the suggestion of a brain, but a brain is well developed only in vertebrates.
Tunicate larvae have visual organs sensitive to light and sense organs responsive to the direction of gravity.
Pigment spots and light receptors in the nerve cord of lancelets detect sudden changes in light intensity. The eyes and other sense organs of vertebrates are more elaborate and complex.
The presence in cephalochordates and vertebrates of a nervous system with segmentally repeated nerves arising from the dorsal hollow nerve cord is suggestive of a common ancestry. The tunicate nervous system does not have the segmentally repeated nerves.
The brains of all vertebrates are greatly enlarged and subdivided into functionally specialized regions. Digestion and nutrition Both tunicates and cephalochordates are filter feeders of small particles of food suspended in the water.
Beating cilia hairlike cellular extensions on the gill slits draw a current of water into the mouth and through the pharynx, where a sheet of mucussecreted by the endostyle a glandular organ lying below the two rows of gill slitsfilters suspended food particles from the water.