Question

Which animals have similar larva to bipinnaria of echinoderms?
A. Branchiostoma
B. Doliolum
C. Saccoglossus
D. Pila

Answer 1

Echinoderms or phylum Echinodermata consists of organisms having radial symmetry and hedgehog-like body appearance. This phylum includes marine animals like starfish, sea urchins, etc. The first stage of larva development in starfish is called the bipinnaria. It is bilaterally symmetrical externally but asymmetric internally.

Complete answer: The Echinodermata phylum is a large group of marine animals, mainly consisting of starfishes. The starfishes develop from an initial larval stage. This larva is called bipinnaria. It is a free-living zooplankton type larva. It seems to have bilateral symmetry from physical appearance or outer appearance. But it has an asymmetric internal body. The larva consists of two bands namely pre-oral and post-oral bands. The bands are ciliated which means covered with hair-like structures. Similar larval stages are seen in Auricularia larva of sea cucumbers.
Let us understand the characteristic features of the larva of each given species to relate them to the bipinnaria of echinoderms.
-Branchiostoma is an eel-like or snake-like marine organism that is related to vertebrates but has no true skull or head. It is also considered similar to echinoderms due to indirect development including the larval stage that resembles closely to the bipinnaria larva as it is ciliated.
-Doliolum has a barrel-shaped transparent body. The larva stage consists of four to five bands of cilia with an apical tuft. The larva of Doliolum does not resemble the bipinnaria of echinoderms.
-Saccoglossus belongs to the genus of acorn worms. They are found in coastal mud and sand habitats. The larval stage is named as miniature acorn worm stage. It is very different as compared to echinoderms.
-Pila is the largest freshwater mollusk. These include apple snails. They are commonly found in freshwater ponds, pools, etc. They are amphibians and have completely different embryology than echinoderms.
So, the right answer is option A, i.e., The Branchiostoma has a similar larva to bipinnaria of echinoderms.

Note: The embryological development of the Branchiostoma is of significant importance as the larva stage resembles both vertebrates and echinoderms equally. It has very simple embryological development and thus easy to be studied. The work of Conklin in 1932 on the embryological development of Branchiostoma is the most accepted one.