Nonvertebrate Chordates, Fishes, and Amphibians

What Is a Chordate? Members of the phylum Chordata are called chordates. A chordate is an animal that has, for at least some stage of its life, a dorsal, hollow nerve cord; a notochord; pharyngeal pouches; and a tail that extends beyond the anus.

Characteristics of Chordates Muscle segments Mouth Pharyngeal pouches Anus Tail Hollow nerve cord Notochord

Characteristics of Chordates The notochord is a long supporting rod that runs through the body just below the nerve cord. Pharyngeal pouches are paired structures in the throat (pharynx) region. The tail can contain bone and muscle and is used for swimming by many aquatic species.

What Is a Chordate? Most Chordates Are Vertebrates About 96 percent of all chordate species are vertebrates.  Most vertebrates have a vertebral column, or backbone.  In vertebrates, the dorsal, hollow nerve cord is called the spinal cord.

What Is a Chordate? As a vertebrate embryo develops, the front end of the spinal cord grows into a brain.  The backbone is made of individual segments called vertebrae.  In addition to support, vertebrae enclose and protect the spinal cord.

Phylogeny of Chordates Sharks & their relatives Bony fishes Amphibians Reptiles Birds Mammals Invertebrate ancestor Jawless fishes Nonvertebrate chordates

Nonvertebrate Chordates The two groups of nonvertebrate chordates are tunicates and lancelets.  Similarities in anatomy and embryological development indicate that vertebrates and nonvertebrate chordates evolved from a common ancestor.  Both tunicates and lancelets are soft-bodied marine organisms.

Tunicates (Larva) Mouth Waste- eliminating organ Hollow nerve cord Tail Notochord Intestine Stomach Heart Larva The larval form of filter- feeding tunicates have all of the chordate characteristics. Pharynx with gill slits

Tunicates (Adult) Tunic Heart Pharynx with gill slits Siphon to mouth Siphon from anus Anus Intestine Reproductive organs Stomach Adult

Lancelets Lancelets are small, fishlike creatures that live on the ocean bottom. Mouth Pharynx with gill slits Reproductive organs Intestine Anus Tail Segmented muscles Notochord Hollow nerve cord

Lancelets An adult lancelet has a definite head region that contains a mouth. As water passes through the pharynx, a sticky mucus catches food particles.  The lancelet swallows the mucus into the digestive tract.

Lancelets Lancelets use the pharynx for gas exchange.  Lancelets are thin enough to exchange gases through their body surface. Lancelets have a closed circulatory system and do not have a true heart.