Which organism is evolutionarily primitive? A snail, a mouse, or a fish?
1 Answer
May be snail: but all these organisms are finely adapted to their respective habitat, including the snail.
Explanation:
Insects breathe air by the tracheal system. (https://socratic.org/questions/how-does-gas-exchange-take-place-in-insects).
Fishes possess paired gills for breathing in water.
(https://socratic.org/questions/what-characteristics-are-common-to-fish)
Mouse is a mammal and there are a pair of lungs for exchanging respiratory gases.
(https://socratic.org/questions/alveoli-in-the-lungs-greatly-increase-what?answerEditSuccess=1)
Compared to those three organisms, snails generally lack a particular respiratory organ. May be this could be regarded as evolutionarily primitive condition of its resiratory system.
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Snails always remain in moist/muddy areas and breathe air through moist skin. Air enters mantle cavity through respiratory pore/pneumostome where surrounding skin remains highly vascularised. Blood carries respiratory gases, and participates in gas exchange.
