Hint: Proboscis is an extended head appendage. It can be observed in vertebrates or invertebrates.
Complete Answer: - Proboscis is an elongated appendage present on the head of animals. In invertebrates, it is present as a tubular structure around the mouth while in vertebrates, it is an extension of the nose called snout. The meaning of this word is to come forward and feed. - In invertebrates it is present as a tubular sucking or feeding organ found in arthropods and molluscs. In Lepidoptera, the mouth mainly consists of the sucking kind, it is called the proboscis or ‘haustellum'. There are two tubes held together by hooks which are separable for cleaning. It is controlled by muscle action. - The tubes are inwardly concave forming a central tube up which is used for sucking. Due to the contraction and expansion of a sac in the head, suction is produced. An example of proboscis being used for feeding can be seen in Deilephila elpenor. In this species, the proboscis is extended forward to attain its food. There are some lepidopterans who lack mouth parts and therefore cannot feed. - Some have mouth parts of the chewing type. It can be used to ingest food including nectar, plant sap, tree sap, dung, etc. A long proboscis can be observed within different groups of flower-visiting insects. - In vertebrates, the trunk of elephant and elongated nose in tapir are called proboscis, is the extended snout of the male elephant seal. The proboscis monkey is named so due to the presence of its enormous nose. Sometimes an abnormal facial appendage accompanying ocular and nasal abnormalities in humans is also called a proboscis.
Note: Proboscis the extension present on the head of animals. It has different functions in different organisms. It can be used as a feeding organ, for respiration, etc, depending on the organism it is present in.