Chordata: Urochordata and Cephalochordata Joycelin Luc Michelle Chen http://www.glaucus.org.uk/diazona0.JPG http://research.myfwc.com/images/gallery/20060309_140447_23656.jpg

Intro to Chordata Have a notochord Have a dorsal nerve cord => develops into central nervous system (brain and spinal cord) Most have pharyngeal clefts and pharyngeal slits Usually have a post-anal tail Explain notocord (longitudinal flexible rod located between the digestive tube and the nerve cord; offers support for animals) and dorsal nerve cord pharyngeal clefts: slits in the body that allows water entering the mouth to exit the body without passing through digestive tract Michelle Chen

Common Names Urochordata Tunicate sea squirts sea pork Cephalochordata Lancelets amphioxus (means “both ends pointed”) http://www.ucmp.berkeley.edu/chordata/urochordata.html (left pic) http://www.biologycorner.com/resources/Lancelet.JPG (right pic) Joycelin Luc

Urochordata http://www.mun.ca/biology/scarr/Ascidian_metamorphosis_2.gif Michelle Chen

Cephalochordata Michelle Chen http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb7pg1_files/amphioxsis.jpg

Body Cavity and Body symmetry Coelom present in both the Urochordata and Cephalochordata subphlya bilaterian (bilaterally symmetrical) Body consists of myoepithelial and Epithelial cells Myoepithelial = helps to expel secretions Epithelium= line cavities; primary body tissue Michelle Chen

Nervous System & Sensory Features Present consisting of brain and spinal cord in Urochordata, nervous system disintegrates when it reaches adult stage Cephalochordates have a simple dorsal nerve cord enclosed in a sheath of collagen fibres which runs the length of the body below the notochord. From this arise a series of smaller nerves which serve the rest of the body. There is no brain or cranium such as we will find in the Vertebrata Michelle Chen http://www.mun.ca/biology/scarr/142007_Urochordata.jpg

Circulatory System Urochordata Blood contains high concentration of vandium and lithium Open circulatory system Ventral heart Cephalochordata Closed blood system Main ventral and paired dorsal aorta No central heart, but consists of branches lacks hemoglobin and is colorless Has Atria cavity Joycelin Luc http://faculty.vassar.edu/mehaffey/academic/animalstructure/outlines/chordata.html

Digestive & Excretory System Urochordata Draws food through siphon into atrium from pharyngeal slits Food filtered by mucous net Moves to esophagus through cilia Exits excurrent siphon Cephalochordata Uses cilia pumping to move food particles from slit Trap food in pharynx Atrium = chamber Michelle Chen

Locomotion/ Musculature Urochordata Juvenile: tail muscles; gravity and light sensitive cells Adult: attach to a substrate sessile Urochordata Juvenile: tail muscles; gravity and light sensitive cells Adult: attach to a substrate sessile Cephalochordata Contraction of muscles arranged in a <<<< structure -> a side to side undulation to move forward Somites Somites = muscle segments developed from blocks of mesoderms; each side of notochord Michelle Chen

Skeletal Type Urochordata Cephalochordata Notochord (some have spicule when young) adult: attach to rock Cephalochordata Develops dorsal, hollow never cord Post-anal tail Joycelin Luc

Reproduction Urochordata Hermaphrodites Eggs kept inside until hatch Sperm released into H2O Cephalochordata Gonochoristic: sex separate Sperm and eggs released into water Fertilization is external Cephalochordata are gonochoristic, meaning the sexes are separate. Both sperm and eggs are released into the water and fertilisation is therefore external Joycelin Luc

Gas Exchange Uses cilia to regulate the gases Pharynx and pharyngeal slits regulate the gas exchange (across external body surface) Michelle Chen

Other unique features Urochordata = very few natural predators Invasive species Form colonies Joycelin Luc

Quiz 1. What are the four basic features that separate Chordata from other phyla? 2. Name one difference between Urochordata and Cephalochordata. 3. How do adult sea squirts move? What about adult lancelets? 4. How are the reproductive methods for Urochordata and Cephalochordata different? Joycelin Luc

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