• The chordates occupy the highest position in the food chain.
• The name phylum was derived from the characteristic which all chordates share, the notochord – a long, elongated, and flexible cartilaginous structure that runs the entire length of the body. (Gr. noto = the back; chorde = string)
• A dorsal nerve cord located above the notochord, it runs the entire length of the body. The nerve cord is a bundle of nerve fibers that connects the brain to the different parts of the body.
• Presence of pharyngeal slits which are openings between the throat and the outside it’s also modified to filter food and gaseous exchange. The pharyngeal slits are supported by gill arches which also had been greatly modified.
• Presence of post-anal tail, an extension of notochord that extends beyond the anus.
• They are bilaterally symmetrical body plan.
• Important: It differentiates them from other animals is the presence of two appendages. These appendages are highly modified for locomotion.
Different Groups of Chordates:
• Invertebrate chordates
-are the chordates whose notochords remain during the entire life of the organisms.
• Vertebrate chordates
-are the chordates that have notochord and pharyngeal slits during early stages of development.
• Cephalochordota(cephalo = head)
- Is represented by the lancelet or amphioxus, a chordate with a fishlike appearance.
-Is an unusual chordate that lives attached to the seabed. The swimming larva of the organism contains the notochord, and all the rest of the distinguishing features of the chordates.
Vertebrate chordates(7 classes)
Three Classes of Fish:
• Class Agnatha(a = not, without; gnathos = jaw).
-This is represented by the lamprey, an eel shaped jawless fish that is considered as the vampire of the ocean.
• Class Chondrichthyes(chondro = cartilage, ichthyes = fish).
-The fish with cartilaginous endoskeleton.
• Class Osteichthyes(osten = bone; ichthyes = fish).
-Class of bony fishes.
• Amphibia(amphios = on both sides, double; bios = life).
-Named because the larval part of the life of the amphibians is spent in water and the adult is on land.
• Reptilia(repere = to creep).
-have bodies covered with dry, cornified scales. Their eggs are leathery.
• Aves(aves = birds).
-have bodies covered with feathers, scaly feet that are adapted to the kind of environment they live.
• Mammalia(mamma = breasts).
-the presence of breasts is a distinguishing feature of mammals. Their breasts are well developed to produce milk. Their bodies are covered with hair.
Subclasses of mammalia:
a.Monotremata(trema = hole).
- have bodies covered with thick fur.
-They’re breasts that lack nipples but secrete milk.
-unique because they are the only egg-laying(oviparous) mammals.
b.Marsupials(marsupium = bag or pouch.
-the marsupium contains nipples that secrete milk.
-The young is born immaturely and crawls in the pouch.
-where the young is nourished as it undergoes development until birth. The largest and the most diverse form of chordates.
Different Orders of Placental Mammals
|Order |Characteristics |Representatives | |Rodentia |Presence of sharp chisel like teeth. |Rats, mice, squirrels, etc. | |Insectivora |Presence of a long snout used for devouring |Moles,...