Diversity Of Phylum Chordata - Essay Example

In fish they are modified to form gills and they may disappear as the animal grows especially in some of the vertebrates. The pharyngeal gill slit is present at some point in life of the animals. Nerve cord: It is hollow and dorsoventrally placed to the notochord and ends in the brain. Other features are muscular tail (post anal tail) and endostyle (a groove like structure in the ventral wall of the pharynx. However the general features exhibited by animals in this phylum are: The animals have a bilaterally symmetrical body Their bodies are segmented and therefore have segmented muscles Their coelom is well developed They have well developed circulatory system with a ventrally placed heart and are therefore more active than their counterpart invertebrates.

Their skeleton is either bony or cartilaginous Their digestive system is complete meaning that their gut runs through the body from mouth to the anus. The phylum chordate falls under the Kingdom Animalia and is further divided into the subphyla Urochordata, Cephalochordata and Vertebrata. However, animals in these subphyla may show different characteristics but the reason for them being grouped in the same phylum is because they exhibit similar characters referred to as unifying links such as urochordates’ larvae have both notochord and nerve cord which vanishes in adulthood.

Cephalochordates have a notochord and nerve cord which persist to adulthood but do not have cranium. In vertebrates, the notochord is replaced with vertebral column at adulthood stage and the nerve cord becomes the spinal cord. Subphylum Urochordata Urochordates also known as Tunicates and exemplified by Ascidia have the following characteristics: At adult stage, their body is covered with a suck like structure (Tunica) and has two siphons one through which water enters the body (incurrent siphon) and the other through which water leaves the body (excurrent siphon).

They are filter feeders and sessile. Although adults are sessile, their larvae are free swimming and exhibit almost all chordate characteristics. Subphylum Cephalochordata Exemplified by amphioxus and lancelets, cephalochordates have eel like bodies, they are marine, their bodies are segmented. Members of the phylum are soft bodied and therefore, cephalochordates are not fossilized. A notochord extends through their elongated body and mouth is armed with cirri which aids in obtaining food. They have numerous gill slits and are also dioecious.

They are filter feeders (extract food from water taken in though the mouth by help of cilia on their wheel organ. Subphylum vertebrata Vertebrates are the most advanced chordates and apart from having an internal skeleton, they exhibit the following characteristics: Their bodies are segmented They have a bilateral symmetrical body Their endoskeleton is either a bony or cartilaginous Pharyngeal gill slits are lost in adults but are present during embryonic stage Their heart is ventrally placed They posses post anal tail They have a closed circulatory system Vertebrata Classes Classes captured are: Agnatha, Chondrichthyes, Osteichthyes,Amphibia ,Reptila ,aves and Mammalia Class Agnatha Agnathans arise from a group of vertebrates known as Cylclostomes (fishes or group of vertebrates without jaws) which excludes Gnathostomes (group of vertebrat