CLASSIFICATIONKingdom: Animalia UROCHORDATA Phylum: Chordata Subphylum: Urochordata (Tunicates) Class: Ascidiacea (Sea Squirts) Anatomy of the Sea Squirt Larvacea (Larvaceans) Thaliacea (Thaliaceans)
GENERAL CHARACTERISTICS- Protochordates • Morphological features: notochord, dorsal hollow central nervous system, pharynx with paired pouches; muscular, post-anal tail - Group of marine chordates in which the notochord is confined to the locomotor tail of the larval stage
GENERAL CHARACTERISTICS- Also known as Tunicates- Enclosed in a delicate, nonliving, and sometimes beautifully colored transparent tunic- Filter-feeders.
CLASS ASCIDIACEA → largest class of urochordates → free-swimming larval stage → sessile as adults, either solitary or colonial
LARVAL STAGE - Body consists of trunk containing the immature viscera and a muscular notochord-supported tail. - The nervous system consists of a dorsal hollow nerve cord, several ganglia and nerves - Respiratory water enters the atrium chamber which is then ejected through the atriopore. - At metamorphosis, the notochord is resorbed and becomes a source of nutrients and rearrangement of the viscera takes place.
ADULT- Incoming water current becomestrapped in the mucus, then the ciliaand esophageal papillae sweep themucus and entrap food particles intothe stomach.- Respiratory water passes over thegills and into the atrium, a fluid-filledcollecting chamber surrounding thepharynx. Gas exchange occurs aswater circulates with the help of theatrial muscles.- One blood vessel from the heartruns anteriorly under the endostyle,and another runs posteriorly to thedigestive organs and gonads.- Gametes may be shed through theexcurrent siphon for externalfertilization or eggs are retained forfertilization and early development.