Introduction to ChordatesChordates are animals that have four structures present atsome stage of their development. postanal tailpharyngealpouches or“gill slits” nerve cord notochord cat embryo at 2 weeksAnimals in this group include tunicates, lancets, fish,amphibians, reptiles, birds, and mammals.
All vertebrate embryos look very similar too each otherbecause they are all chordates. Note that all of these chordates have: a notochord, postanal tail, nerve cord, and pharyngeal pouches.
NotochordAll chordates have an internal notochord that supports theanimal and extends along the upper part of the body (whatwe think of as the back. - The notochord is a firm but flexible structure made up of fluid- filled cells that are enclosed in a stiff covering. - The notochord extends into the postanal tail which is a muscular structure at the end of the developing chordate. - In most chordates (fish, amphibians, reptiles, birds and mammals) the notochord gets replaced by the back bones or vertebrae - Other chordates such as the tunicate and the lancet, the notochord is kept into adulthood.
Tunicates and Lancets Lancets a.k.a. amphioxus are primitive eel-like chordates that spend mostTunicates a.k.a. sea squirts are of their time buried in sand.sessile marine chordates. They contain typicalAs larvae they are free chordate features.swimming and contain Both tunicates and lancetsnotochord, nerve cord, andother chordate features. are invertebrates.
Nerve CordAbove the notochord is a tube-like structure called thenerve cord.- As most chordates develop, thenerve cord enlarges and becomesthe central nervous system.- The front end of the nerve cordenlarges and becomes the brain. nerve cord- The remainder of the nerve nerve cordcord becomes the spinal cord.
Pharyngeal PouchesPharyngeal pouches are sac-like projections found in theregion between the mouth and digestive tube.- Many chordates have several pairsof pharyngeal pouches.- Ancient invertebrate chordatessuch as tunicates and lancetsuse them for filter feeding.- In fish pharyngeal pouchesbecome gills Pharyngeal- In humans pharyngeal pouches pouchesare present only duringembryonic development.
VertebratesVertebrates make up the largest group of animals in thechordate phylum. They include jawless fish, jawedcartilaginous fish, bony fish, amphibians, reptiles,birds, and mammals.Vertebrates contain all chordate characteristics plus … - endoskeleton made up of bones and cartilage - backbones (vertebrae) that protects the spinal cord - skull that protects the brain Because vertebrates are animals, they also have all the characteristics of animals that we learned earlier.
Ectotherms and EndothermsVertebrates can be divided as ectotherms (cold-blooded)or as endotherms (warm-blooded). Ectotherms include Endotherms include fish, amphibians, and birds and mammals. reptiles. - Their internal body - Their core body temperature changes temperature is kept with the temperature of nearly constant its surroundings. through thermal homeostasis.
Origin of ChordatesChordates are believed to have descended fromechinoderm-like ancestors during the Precambrian period.