Chapter 34: Vertebrates

1. Chapter 34: Vertebrates By Amelia Abuzuhri and Katherine Duffy

2. Section 1: • Name is derived from the series of bones that make up vertebral column or backbone. • Vertebrates are members of Chordates, which is a group made up of vertebrates and some closely related invertebrates. • Chordates are bilaterian animals and belong to clade known as Deuterostomia. • Chordates are named for a skeletal structure, the notochord.

3. Section 1: Characters of Chordates • Notochord is longitudinal, flexible rod located between digestive tube and nerve cord. Present in all chordate embryos and some adult. • Composed of large fluid filled cells enclosed in fibrous tissue. Provides skeletal support throughout length of chordate. • Notochord provides firm but flexible support against which the muscles work during swimming. • In humans the notochord is made up of gelatinous disks between vertebrae.

4. Characters: Notochord cont.

5. Characters:Dorsal, Hollow Nerve Cord • Nerve Cord develops from plate of ectoderm, during the embryo stage, it rolls into tube located located dorsal to notochord. • Dorsal is a hollow nerve cord which is unique to chordates; other animal phyla have solid nerve cords and are located ventrally. • This nerve cord of the embryo later develops into the central nervous system--> brain and spinal cord.

6. Characters: Pharyngeal Slits or Clefts • During embryonic stage in chordates there are a series of pouches separated by grooves along the pharynx, Pharyngeal clefts. • These grooves later develop into Pharyngeal Slits which allow water to enter the mouth without passing through the digestive system. • In most vertebrates these slits are modified for gas exchange and are known as gill slits. • However in tetra pods, clefts don’t develop into slits but into other structural parts.

7. Lancelets • Bladelike shape and lack a backbone, but do have: notochord, dorsal, hollow nerve cord, pharyngeal slits, and post-anal tail. • Adults can reach up to 5cm, closely resemble idealized chordate, and are members of subphylum Cephalochordata. • Burrow in sand of seafloor and leave cilia exposed to obtain nutrients. Use contractions of muscles to swim.

8. Tunicates • SubphylumUrochordata; are more closely related to chordates than Lancelets. Chordates characteristics more apparent in larvae stage. • Finds substrate in water and attaches and looses all chordate characteristics.

9. Section 2 • Craniates chordates with a head. • Have 2 Hox gene clusters (lancelets/tunicates have 1) and have a neutral crest. • Neutral crest collection of cells near dorsal margins in embryo. Gives rise to various structures in body. • More active, higher metabolic rate, and more extensive muscular system. • Hagfishleast developed craniate. Have skull but lack jaw and vertebrae are snakelike. • Secrete a slime to drive away predators which sticks to gills of predator then suffocating it.

10. Craniates • Haikouella craniate discovered in 1999 in southern China. • Hagfish is in the class of Myxini.

11. Section 3: • Vertebrates branched off from other craniates, and transcribed new gene factors Dlx family resulted in more genetic complexity (extensive skull/backbone). • Lampreys (oldest living lineage of vertebrates) are a parasite in marine/freshwater environments with clamping mouths that tend to feed on fish blood. • Have relatively short life span, after they reproduce they die within a few days. • Lamprey cartilage is unlike most vertebrae in that it contains no collagen, it is a stiff protein matrix.

12. Conodonts/Orgins of Bone and Teeth • Conodonts were a slender, soft-bodied vertebrate with prominent eyes and teeth. • Teeth were barbed like books made of dental tissue that were mineralized. Gave way to discovering vertebrates without jaws, but with teeth. • Mineralization was only discovered after lampreys were, this gave way to divergence of unmineralized skeleton to mineralized.