Chapter 34 Vertebrates

1. Chapter 34 Vertebrates Barbara Musolf Clayton State University A&S Building G 110-G 678-466-4851

2. Objectives Know the chordate characteristics Notocord Dorsal hollow nerve cord Pharyngeal basket Post-anal tail

3. Fig. 34.2)

4. Origin of backbones A slender 2 cm slender marine organism gave rise to vertebrates 500 million years ago Vertebrates were restricted to the ocean for 200 million years 360 million years ago they moved to land Vertebrates gave rise to the largest and heaviest organisms (plant-eating dinosaurs) to walk on land and the largest that exists in the ocean (Blue whale). Vertebrates produced an organism with language, complex tool-making skills and symbolic thinking.

5. Chordata (Fig. 34.4) Bilaterian deterostomes Derived characteristics Presence of a notocord Dorsal hollow nerve cord Pharyngeal gill slits Muscular post-anal tail A notocord is a longitudinal, flexible tube between the digestive tube and nerve cord that provides support. It disappears or is reduced in organisms with a jointed endoskeleton. In humans it is present during early development but then is reduced to the gelatinous discs within the fibrocartilage discs that cushion the vertebrae Dorsal hollow nerve cord develops from ectoderm that rolls into a tube that dorsal to the notocord. This becomes the organism�s central nervous system. The hollow area makes up the vertebral canal and ventricles of the brain. The pharynx is just posterior to the mouth and the gill slits are a series of pouches that form along the side of the pharynx. Gill slits allow water to enter the mouth region and exit the body without entering into the digestive tract. They are used by suspension feedrs and for gas exchange. In terrestrial vertebrates they develop into parts of the ear and other structures of head and neck. Most organisms have a digestive tract that extends the entire length of the organism. Chordates have skeletal structures and muscles that extend beyond the anus that help in locomotion, particularly in aquatic animals. A notocord is a longitudinal, flexible tube between the digestive tube and nerve cord that provides support. It disappears or is reduced in organisms with a jointed endoskeleton. In humans it is present during early development but then is reduced to the gelatinous discs within the fibrocartilage discs that cushion the vertebrae Dorsal hollow nerve cord develops from ectoderm that rolls into a tube that dorsal to the notocord. This becomes the organism�s central nervous system. The hollow area makes up the vertebral canal and ventricles of the brain. The pharynx is just posterior to the mouth and the gill slits are a series of pouches that form along the side of the pharynx. Gill slits allow water to enter the mouth region and exit the body without entering into the digestive tract. They are used by suspension feedrs and for gas exchange. In terrestrial vertebrates they develop into parts of the ear and other structures of head and neck. Most organisms have a digestive tract that extends the entire length of the organism. Chordates have skeletal structures and muscles that extend beyond the anus that help in locomotion, particularly in aquatic animals.

6. Cephalochordata Lancelet adults have all 4 chordate characteristics Segmentation appears as somites Feed by swimming up into the water column and then trap plankton in their pharynx as they sink. The swimming resembles swimming of fish. They produce side to side undulations that propel the organism forward. The serial musculature which shows in the chevron organization of muscle fibers is evidence of segmentation. The blocks of muscle (mesoderm) are called somites and they are found along the notocord of all chordates. Lancelets are rare however in places such as Tamp Bay FL they are quite dense.The swimming resembles swimming of fish. They produce side to side undulations that propel the organism forward. The serial musculature which shows in the chevron organization of muscle fibers is evidence of segmentation. The blocks of muscle (mesoderm) are called somites and they are found along the notocord of all chordates. Lancelets are rare however in places such as Tamp Bay FL they are quite dense.

7. Urochordata Tunicates descend from the earliest branch of the chordate tree. Characteristics of chordates are evident in the larva Adult tunicates are sessile and lack chordate structures such as notocord and tail Protect themselves by shoot a jet of water from its excurrent siphon.

8. Urochordate�tunicate (Fig. 34.4)

9. Early chordate evolution (Fig. 34.6) The Hox genes in lancelet that organize the anterior-posterior development of the nervous system are similar to vertebrates