Polypterus

Polypterus is a genus of freshwater fish in the bichir family (Polypteridae) of order Polypteriformes. The type species is the Nile bichir (P. bichir). Fishes in this genus live in various areas in Africa. Polypterus is the only known vertebrate to have lungs, but no trachea. The etymology of the genus name derives from a combination of the Greek prefix πολυ-, poly- (many) and the root word πτερον, pteron (wing or fin) – 'many fins'. In shallow water, Polypterus inhales primarily through its spiracle (blowhole). Exhalation is powered by muscles in the torso. During exhalation, the bony scales in the upper chest become indented. When the muscles are relaxed, the bony scales spring back into position, generating negative pressure within the torso, resulting in a rapid intake of air through the spiracle. The air is nearly sufficient to fill the lungs. This is followed by one cycle of buccal (mouth) pumping, which 'tops off' the lungs, with the surplus air from the buccal pumping process discharged through the pharynx. According to one hypothesis, Devonian tetrapods may have inhaled in this way. Polypterus was discovered, described, and named in 1802 by Étienne Geoffroy Saint-Hilaire. It is a genus of 10 green to yellow-brown species. Naturalists were unsure whether to regard it as a fish or an amphibian. If it were a fish, what type was it: bony, cartilaginous, or lungfish? Some regarded Polypterus as a living fossil, part of the missing link between fishes and amphibians, helping to show how fish fins had evolved to become paired limbs. In 1861, Thomas Huxley created the order Crossopterygii to house animals, fossil and living, that possessed lungs and fleshy pectoral fins with lobes. He placed Polypterus and Calamoichthys within this order, allocating them to a new tribe, Polypterini, which he created especially for them. The weight of Huxley’s authority allowed this allocation to last in textbooks and lectures long after it had been disproved. In the 1870s and 1880s, Francis Balfour and his students had shown that embryology could help to answer questions about the evolution of species. No one had studied the embryology of Polypterus. Someone who could do this might prove the “missing link” theory and be greatly honoured, but it could be a dangerous quest. The only breeding Polypterus specimens were in swampy parts of African rivers. Africa was a turbulent place and swamps were rich breeding grounds for mosquitoes carrying malaria. Two men, Nathan Harrington and John Samuel Budgett, attempted to answer this question by making repeated expeditions to Africa. Harrington failed on his first attempt in 1898 and died early on his second in 1899 before he could reach his destination. Budgett failed in 1898/9, 1900, and 1902. He finally succeeded in 1903, but died of blackwater fever shortly after his return to England. He left excellent samples and drawings, but his only writing was a diary. Consequently, his results on Polypterus were written up and published by his friend John Graham Kerr.