Question

Adult tunicates show
A. All chordate characters
B. No chordate characters
C. Some chordate characters
D. Only dorsal nerve cord

Answer 1

Hint: Tunicates belong to the subphylum Tunicata, under phylum Chordata. Tunicate was previously known as Urochordata. Tunicates are believed to have originated as early as the Cambrian period. They demonstrate certain developmental resemblance to the animals belonging to phylum Chordata.

Complete answer:
Chordates are vertebrate animals and possess certain characters at any of its developmental stages. The important chordate characters present are presence of notochord, pharyngeal gill slits, a dorsal nerve chord and a post-anal tail.
Tunicates are animals that are covered by a cellulose containing outer sheath or a ‘tunic’, hence the name. Animals that belong to this subphylum show developmental affinity to the Chordates.
The tadpole larva of the tunicates has the notochord, dorsal nerve cord and a tail. While the larva metamorphoses into an adult, the tail, nerve cord and notochord are lost. The gill slits are retained by the adults. Although the adult tunicates do not have a clear body cavity, they possess an ectoderm, mesoderm and endoderm. The organs of the body with the exception of heart, reproductive organs and the branchial sac, are enclosed in a sac like pericardium. The pericardium is surrounded by the jelly like mesoderm. They also have a well-developed circulatory system – the heart is located below the gut, the blood vessels are composed of simple connective tissue, and comprises blood corpuscles. The tunicate brain is a hollow cerebral ganglion and is called the neural tube.
In adults, the characters that are common to chordates are much less. The adults do not contain a notochord and a post anal tail. Adults do not contain the body segmentation found in chordates. However, all the characteristics of the larval tunicates are similar to that of the chordates. The larval characters bear close relationship with the chordates. Thus, the larva shows more common characters with the chordates while the adults bear some chordal characteristics.

Hence, the correct answer is option (C).

Note: Tunicates are found in marine environments. The adult forms possess a tunic-like covering of its body from which these animals derive their name Tunicates. The animals can be sessile or free floating. Tunicates show affinity towards chordates. However, the distinct chordate characters are lost during the process of metamorphosis and the adult forms retain only some chordate characters.