Question

Only vertebrates to lack epidermal scales are
A) Fishes
B) Reptiles
C) Bird
D) Mammals

Answer 1

Hint:The only vertebrates to lack epidermal scales are a class of organisms that are found in marine and freshwater habitats, with a streamlined body and double-chambered heart. These organisms are also cold-blooded which means that they cannot regulate their body temperature.

Complete answer:
The only vertebrates to lack epidermal scales are fishes as their scales are mesodermal in origin. Epidermal scales are the scales that arise from the outermost embryonic layer known as the epiderm. Instead, fishes of class Chondrichthyes have placoid scales and fishes of class Osteichthyes have ctenoid scales both of which are mesodermally originated.

Chondrichthyes is a class of fishes that have cartilaginous endoskeleton and their teeth are made up of modified placoid scales. Whereas Osteichthyes is a class of fishes that have bony endoskeleton and entire skin covered with ctenoid scales. Examples of Chondrichthyes include Scoliodon (Dogfish), Carcharodon (Great white shark), Trygon (Stingray). Examples of Osteichthyes include Hippocampus (Sea horse), Labeo (Rohu), Pterophyllum (Angelfish).

Additional information:
Reptiles: This class includes organisms whose mode of locomotion is creeping or crawling. They have dry bodies that are covered by epidermal scales or scutes and they are mostly terrestrial. Examples include Chameleon (Tree lizard), Chelone (Turtle), Naja(Cobra).

Birds: The characteristic feature of birds or Aves is the presence of feathers and pneumatic hollow bones. Scales are present on the hind limbs whereas the forelimbs are modified into wings. Examples include Corvus (Crow), Columbia (Pigeon), Psittacula (Parrot).

Mammals: The characteristic feature of Mammals is the presence of milk-producing mammary glands to nourish the young ones. Examples include Elephas (Elephant), Panthera tigris (Tiger), Macropus (Kangaroo).

Hence, the correct answer is option ‘B’ i.e, 'Fishes'.

Note:
-Notochord is present throughout the life cycle of the fishes of Chondrichthyes.
-Chondrichthyes do not have an air bladder and thus have to swim constantly in order to avoid sinking whereas an air bladder is present in Osteichthyes which helps in buoyancy.
-Birds and Mammals are the only vertebrates that are warm-blooded.