Govt Exams
The evolutionary sequence of animal phyla based on fossil records and molecular evidence shows Sponges (Cambrian), followed by Cnidarians, Flatworms, Arthropods, and later Chordates.
Fish gills operate on a countercurrent exchange principle where blood flows opposite to water flow, maximizing oxygen extraction efficiency to about 80-90%.
In triploblastic animals: Ectoderm forms nervous system and epidermis, Mesoderm forms muscles and connective tissue, and Endoderm forms the digestive tract and associated glands.
Radial and indeterminate cleavage are characteristics of deuterostomes, which include Echinodermata and Chordata. This contrasts with the spiral cleavage of protostomes.
Amphibian skin is moist, permeable, rich in mucous glands, and participates in respiration. Unlike reptiles, it is NOT heavily keratinized, which would reduce water absorption.
Parthenogenesis allows rapid population growth in isolated or newly colonized environments where finding mates might be difficult, without requiring genetic diversity maintenance.
Birds retain scales on their legs/feet, a feature inherited from theropod dinosaur ancestors. This homologous structure provides evidence of their evolutionary relationship.
Echinoderms are enterocoelomates where the coelom develops from the wall of the archenteron (primitive gut). This is a characteristic of deuterostomes.
Echinoderms have distinct oral (mouth) and aboral (opposite of mouth) surfaces. This is related to their radial symmetry pattern.
Agnathans (lampreys, hagfish) lack paired fins and jaws, while gnathostomes possess these structures along with true jaws derived from gill arches.