Question

An animal which has both exoskeletal and endoskeletal structure is a
A. Freshwater mussel
B. Tortoise
C. Frog
D. Jellyfish

Answer 1

Hint: Exoskeletal is the ridge external skeleton whereas endoskeleton is the internal skeleton made up of rigid material like bone. Some vertebrates contain shells or armored skin differentiation.

Complete answer:
A skeletal gives the structural support to the animals as well as humans. It helps in the movement, locomotion as well as protecting the inner organs. Skeletal may be exoskeleton (outward) and endoskeleton (inner). Some animals contain exoskeleton, some contain endoskeleton and some have both of them.
Exoskeleton is a rigid covering found on the surface of an animal. These rigid coatings shelter the muscles, tissue and other body organs. It gives protection to the animals from predators. The exoskeleton acts as a protective coating for the animal with the calcified shells within them. Exoskeleton is mostly found in the insects and soft body animals like snails, mussels. Endoskeleton is composed of bones and cartilage and is supported by the connective tissues. Bones are composed of bone cells called osteoblasts. Exoskeleton is mainly found in the vertebrates like reptiles, fishes and mammals. It is the living structure which protects the internal organs.
Freshwater mussel belongs to the family Mollusca which are invertebrates. It contains soft inner body and a rigid outermost shell. The soft tissue helps them in locomotion. Each Mollusca contains two shells which shelter them from the predators. These organism have exoskeletal structure. Frog belongs to amphibian family. It lives in both water and land. It is a functional endoskeleton as the body contains bones which are situated in the internal part. It also contains organs like lungs and heart. Endoskeleton helps these organisms in jumping and swimming. Jellyfish belongs to the family Cnidaria which are invertebrates with the hydrostatic skeleton. It does not contain bone or cartilage but it consists of a cavity named coelom which is occupied by gelatinous substance. Water exerts the hydrostatic pressure on their wall for the movement. So they are neither endoskeleton or exoskeleton.
Tortoise belongs to class Reptiles and are vertebrates so they contain endoskeleton as their body contains bones and cartilage. Tortoises have an adaptation called a shell which is modified into a rib cage, sternum. The shell is the outer layer which protects them from the predators. The shell acts as an exoskeleton for tortoises. So the tortoise contains both exoskeleton and endoskeleton.

Therefore the correct option is B.

Note: Leatherback shell is one of the longest shells found around 2.4 m long. The top part of the tortoise shell is called carapace and the underside is the plastron. The tortoise shells are made to avoid the build-up of lactic acid.