Question

Pigment hemocyanin is found in
A. Chordata
B. Annelida
C. Porifera
D. Mollusca

Answer 1

Hemocyanin is a non-heme copper-containing protein that is present as a respiratory pigment in certain invertebrate animals which helps them to transport oxygen throughout their body. It is a protein that carries oxygen and is found in mollusks.

Complete answer:
Hemocyanin is a protein that is found in invertebrate animals. Certain, invertebrate animals require hemocyanin as their respiratory pigment to facilitate the transportation of oxygen throughout their body. So, here the answer will be Mollusca.

Mollusca is the second-largest phylum of invertebrate animals. They are mostly marine and a few live in freshwater while some of them are of the terrestrial form (living on the ground). They contain gills known as ctenidia (it has a comb-like structure and its central part consists of many filaments or plate-like structures that protrude out of it. This hangs into the mantle cavity and due to this a large surface area is created for gaseous exchange) or lungs (in the terrestrial form) which helps them in respiration.

The hemocyanin which is present as a respiratory pigment in the phylum Mollusca does not contain a heme group and a cyanide ion (as the name suggests) rather it is a non-heme copper-containing protein which simply means blue blood.

Hemocyanin never exists as a monomer rather it always exists with several subunits. Each subunit contains a long protein chain that is present in a folded pattern. This folded protein chain of one subunit of the hemocyanin is buried within the metalloprotein which is adjacent to two copper centers. The copper atoms do not have any bond between them and they are bounded by three histidine residues.

Additional information:
Hemocyanin is also present in Arthropoda (it is the largest phylum of invertebrates). Although the gross molecular structure of hemocyanin is a little bit different, they both have the same dioxygen binding centers.

Note: Hemocyanin is the respiratory pigment of certain invertebrate animals which simply means blue blood and is usually found in invertebrates. It doesn't contain a heme group and is rich in copper. Hemocyanin is the central atom in the copper.