Question

The larval form of urochordates is called as
A. Tornaria
B. Tadpole
C. Veliger
D. Pluteus

Answer 1

Hint: The fertilized eggs of urochordates undergo holoblastic and unequal cleavage. The egg develops to form the blastula. The blastula shows upper micromeres and lower macromeres. When the invagination of the macromeres occurs, gastrulation takes place, and the structure of the gastrula is formed. This gastrula develops into a tailed larva.

Complete answer: Tunicate, also called urochordate are organisms belonging to the subphylum Tunicata or Urochordata of the phylum Chordata. Tunicates are small marine animals that are found diversely in many marine ecosystems around the world. Tunicates are distributed in ocean waters from the polar regions to the tropics. Free-swimming tunicates are found throughout the oceans as plankton, while sessile forms grow mainly on solid surfaces such as wharf piles, ship hulls, rocks, and the shells of various sea creatures. Adult members are commonly embedded in a tough secreted tunic containing cellulose. The less modified forms are benthic or bottom-dwelling organisms whereas more complex forms are pelagic or found in open waters. A characteristic tadpole larva develops in the life cycle, and most chordate features disappear at metamorphosis. The larval stage is very short, and the larva does not feed but focuses on finding a suitable place for the adult to live. The larva is free-swimming and exhibits all chordate characteristics. It has a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail and called a tadpole. The muscular tail of the tadpole larva accounts for two-thirds of the larval body. As mentioned it has a notochord and a nerve cord. After a period of few days, the larva will attach itself to a surface to being its metamorphosis. As the larva metamorphoses into an adult, the tail resorbs, providing food reserves for the developing animal. Free-swimming tunicates metamorphose without attachment.
Therefore, the correct option B.

Note: Urochordates as commonly referred to as tunicates. This organism is a member of the Urochordata subphylum of the Chordata phylum. Its name means partial chordate to indicate they rarely show chordate characteristics as an adult. Only the larva shows a notochord which disappears as they mature. The larva often looks like a tadpole with a head and a long tail and therefore are referred to as tadpoles.