The Chordates – Phylum Chordata Three Sub-Phyla Urochordata – tunicates Cephalochordata – lancelets Craniata (Vertebrata) Marine, no Backbone, less Complex than vertebrates tunicate lancelet

Characteristics of ALL Chordates At some time in their development, chordates: Have nerve cord – dorsal and hollow Have notochord – flexible, rodlike supporting structure (turns into backbone) Have gill slits – paired in throat region (seen only in embryo for some chordates) Have a post-anal tail

Urochordata Tunicates (sea squirts) Free-swimming larva has all of the characteristics of chordates Sessile, filter feeders as adults. Most structures of chordates have developed into other structures or have degenerated.

Cephalochordata Amphioxus – lancelet Label: mouth tentacles gill slits intestine dorsal nerve cord notochord anus tail

Characteristics of Craniates (Vertebrates) Anterior part of nerve cord is brain 3 body sections – head, neck and trunk Tail during some stage of development Jointed, internal skeleton 2 pairs of appendages Heart has 2-4 chambers, closed circulatory system Gas exchange in lungs or gills Large body cavity called coelom Skin has 2 or more layers

8 Classes of Craniates (Vertebrates) Myxini - Hagfishes Cephalaspidomorphi - Lampreys Chondrichthyes - Cartilaginous Fishes Osteichthyes - Bony Fishes Amphibia Reptilia Aves - Birds Mammalia lamprey Hagfish

Cephalaspidomorphi Ammocoetes larva Label: Oral hood External gill openings Heart Intestine Anus Caudal fin Brain Notochord Spinal cord

Cephalaspidomorphi - Lampreys All species of lampreys spawn in freshwater streams Eggs hatch releasing small (1cm) Ammocoetes larvae Ammocoetes burrow in sand or mud in streams and emerge at night to filter feed. The larval period lasts from 3-7 years.

Parasitic lampreys are either marine or freshwater forms. Parasitic lamprey adults attach themselves with their sucker-like mouths to fish and rasp through flesh and suck body fluids. To prevent blood clotting, the lampreys inject an anticoagulant into the wound. When gorged, the lamprey releases itself, often leaving a fatal wound.

Parasitic freshwater adults live a year, spawn and then die Parasitic marine adults may live longer

Nonparasitic lampreys do not feed after they emerge as adults Their GI tract degenerates into a nonfunctional strand of tissue They die within a few months after they spawn.

Internal Anatomy of the Lamprey Mouth Teeth Tongue Pineal eye complex Naris Olfactory sac Brain Spinal cord Intestine Ovary/testis Heart gills