Chordata

Chordata: Us & others too Chordata Phylum of coelomate animals having a notochord and gill clefts in the pharynx at some point in their life history, and a hollow nerve cord running dorsally, with the anterior end usually dilated to form a brain. The chordates include the vertebrates, the cephalochordates, and the urochordates Urochordata [Tunicata] subphylum of chordates containing the classes Ascidiacea, and the Thaliacea; Chordate features are found only in the larva and are generally lost in the adult. The adult secretes a tough cellulose sac (tunic) in which the animal is embedded Cephalochordata Subphylum of small cigar-shaped aquatic chordates commonly called lancets and including amphioxus. They have a persistent notochord in the adult and a large sac-like pharynx with gill slits for food collection and respiration Vertebrata Subphylum of Chordata, animals characterized by the possession of a brain enclosed in a skull, ears, kidneys and other organs, and a well-formed bony or cartilageous vertebral column or backbone enclosing the spinal cord. Notochord Slender rod of cells of mesodermal origin running along the back of the early chordate embryo and which directs formation of the neural tube. It persists in primitive chordates but in vertebrates is replaced by the spinal column Atrium Various chambers/cavities; chamber surrounding pharynx in tunicates & cephalochordates Endostyle Longitudinal groove in ventral wall of pharynx in urochordates and some primitive chordates, involved in mucus secretion Stigmata The “slits” which allow water to pass through to the gills Tunic The body wall or test of a tunicate Paedomorphosis Evolutionary change which results in retention of embryonic structures in adult animals Neoteny Growth rate of body form slowed so that adult form not attained before reprod. Maturity Progenesis Precocious maturation of gonads in larva that then stops growing, and never becomes an adult Chordata – invertebrates (1 & 2 class: no cranium) o Urochordata tunicates: marine, sessile, filter-feeders o Cephalochordata lancents: between worm & fish, not very active, filter-feeders o Vertebrata Craniates: (Cranium, a bony structure around brain) & vertebral column (protects the nerve cord) Hallmarks of Chordata (5) o Notochord flexible rod-like structure extending throughout the body [flexible, not compressible]  First part of endoskeleton to appear in embryo (remains for life in primities)  Replaced by Vertebrae in most chordates (vertebrates  Axis for muscle attachment (bends without shortening- permits undalatory body movement (swimming)) – FACILITATES EFFICIENT SWIMMING o Dorsal Nerve Cord always DORSAL to GI tract (initially tubular) [note others was ventral]  Anterior end enlarged  brain  Vertebrates nerve cord passes through protective neural arches of vertebrae  brain enclosed by cartilageous cranium (bony structure ‘skull’)