Govt. Exams
The production of milk through mammary glands is the defining characteristic of mammals (Class Mammalia). While other features may be shared, lactation is unique to mammals.
Flatworms (Platyhelminthes) use flame cells (protonephridia) for osmoregulation and excretion. Nephridia are found in annelids, Malpighian tubules in insects.
Insects and other arthropods have an open circulatory system where hemolymph bathes the organs directly. Vertebrates have closed circulatory systems.
Cnidarians (hydra, jellyfish, corals) have tentacles, radial symmetry, and nematocysts, but do NOT have a segmented body. Segmentation is characteristic of Annelida and Arthropoda.
Mammals are uniquely characterized by mammary glands for milk production and hair/fur for insulation, not all have placenta (monotremes lack it).
Most sponges are marine organisms. They lack true tissues, organs, and nervous systems but can reproduce both sexually and asexually.
Fish possess a two-chambered heart with one atrium and one ventricle, unlike amphibians and reptiles which have three chambers.
Amphibian skin is thin, moist, and richly supplied with blood vessels, enabling efficient cutaneous respiration.
The radula is a ribbon-like feeding structure with teeth found in gastropods (snails) and many other molluscs, used for scraping food.
Analogy refers to similar structures with different origins performing similar functions (e.g., bat wing and bird wing).
