Larval tunicates (Urochordata) posses all four structures that classify chordates, but adult tunicates retain only pharyngeal slits. Larval tunicates swim for a few days after hatching, then attach to a marine surface and undergo metamorphosis into the sessile adult form. The life-history of urochordates passes through a dramatic change. Their chordate characters are more pronounced during larval period. While in adults they are more like invertebrates than chordates. Therefore, the characters are described in two heads — larval characters (Fig. ) and adult characters (Fig. ).
Mar 05, · Adult lancelets retain all five key characteristics of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. Urochordates, commonly known as tunicates, differ from other chordate subphyla (Cephalochordata and Vertebrata) in that the adult form has no notochord, nerve cord, or tail. In fact, an adult tunicate is an immobile, filter-feeding marine animal that in some ways looks more like .
Jun 26, · The notochord may or may not persist in the adult, and the pharyngeal slits are modified in various ways in the different groups. The Urochordates are the probable ancestors of vertebrates. Vertebrates have a dorsal nerve cord that is protected by a vertebral column, and the anterior portion of this nerve cord is protected by a cranium. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail (Figure 2). In some groups, some of these are present only during embryonic development. The chordates are named for the notochord, which is a flexible, rod-shaped structure that is found in the embryonic.