Living Agnathans Lamprey Dissections

Agnathans The vertebrate story begins with the Agnathans Agnathans lack jaws, a biting apparatus derived from pharyngeal bars. Today, hagfishes and lamprey carry the history of the jawless fish. These two groups, together, form the Cyclostomes and are used to represent primitive vertebrates. However, they are modified and adapted to specialized lifestyles, and therefore depart in several ways from primitive agnathans.

Myxinoidea The hagfishes- deep sea, mud burrowing, eel-like scavengers. The use tooth-like processes on a muscular tongue to rasp the flesh from prey. Slime glands beneath the skin release mucus through surface pores. Hagfishes have a unique ability t tie themselves into a know and use the slime to slip through his know.

Hagfishes have no trace of vertebrae on or around the notochord. Their osmotic concentration is unique. Their internal osmotic concentration is roughly that of seawater, so there is no net flow of water into or out of their tissues. Due to this it is believed that hagfishes are the only extant fishes to have a saltwater ancestor.

Petromyzontida Lampreys are a mostly parasitic, freshwater agnathan. Lampreys use the “teeth” around their mouth to grasp onto prey, and a rasping tongue to pierce the flesh of their host. Larval lamprey are referred to as ammocetes, and undergo metamorphosis into the adult form. As larvae they possess all five chordate features and life as suspension feeding individuals. Lamprey lack bones and surface scales. Adults possess: medial fins, but no paired fins Vertebrae, represented as individual blocks of cartilage that sit atop the notochord.

Lab Objectives Today you will dissect a lamprey. You will be looking for evidence of the 5 chordate features along with derived vertebrate features. Prior to dissection you will also identify certain external features.

Dissection Externally: Internally Transverse and Sagittal Sections) Dorsal Fins (Anterior and posterior) External Gillss Eye Oral Funnel Internally Transverse and Sagittal Sections) Notochord Pharyngeal Gills Ovary/Testis Heart (ventricle) Myomeres Liver Kidney