Question

Retrogressive metamorphosis is found in
(a) Balanoglossus
(b) Branchiostoma
(c) Herdmania (Urochordata)
(d) All of the above

Answer 1

Hint: Metamorphosis is the change in the body structure from the larval stage to the adult stage. Retrogressive metamorphosis is considered as the development of a better-developed larva to the less-developed adult form.

Complete Answer:
Herdmania is also known as sea squirts which comes under Urochordata in which larva undergoes a retrogressive metamorphosis. In retrogressive metamorphosis, the well developed active larva with the presence of notochord gets metamorphosed into less developed non-chordate sedentary adults. In urochordates, the nerve cord in larvae gets replaced into dorsal ganglion in adults. The body is covered with a leathery tunic which is made up of cellulose substance. Doliolum and Salpa is also an example of Urochordata.

Additional information: Balanoglossus comes under phylum Hemichordata which is first considered under chordates but then placed under non-chordates due to high similarity with non-chordates. In this sexes are separate and development include free swimming tornaria larva and fertilization takes place externally. The body of Balanoglossus is soft, unsegmented, and divided into proboscis, collar, and trunk. The circulatory system consists of the dorsal heart and dorsal and ventral vessels which are interconnected by lateral vessels and sinuses. The nervous system is primitive consisting mainly of intraepidermal nerve plexus.
Branchiostoma is also known as Amphioxus and lancelet in which the notochord extends in the anterior end of the body and persists throughout life. The brain is not present and gill slit are more numerous which opens into artium. The tail is present from the larval stage to the adult stage.
So, the correct answer is Herdmania (Urochordata).

Note: Parker and Haswell in 1962 have placed hemichordata into phylum Chordata, then in 1974 Barnes placed hemichordata into separate phylum under Invertebrate and in 2005 Benton, M.J placed hemichordata as a phylum under invertebrate.