Q.What are the difficulties that you would face in classification of animals, if common fundamental features are not taken into account?

Classification rests on deep, shared fundamental features rather than on outward appearance. If those common features were ignored, several problems would follow:

• With over a million described species, there would be no orderly way to group animals, so the sheer diversity would become unmanageable.
• We would be forced to study every single species separately, instead of examining a few representative types that stand for a whole group.
• A newly discovered animal could not be slotted into any definite, systematic position alongside its relatives.
• Grouping by superficial looks would place unrelated animals together and separate truly related ones, giving a false picture of relationships.
• Comparison and communication between biologists would break down, because there would be no agreed framework of characters to refer to.

Animals differ enormously in shape and internal structure, and more than a million species have already been described. On a scale of diversity like this, some orderly way of grouping animals is not a luxury but a necessity. The whole point of classification is that, despite all their outward differences, animals share certain deep, fundamental features — the level of organisation of their cells, the type of body symmetry, the number of germ layers, the nature of the coelom, the presence of segmentation, and the presence or absence of a notochord. These shared characters, not surface appearances, are what a sound classification is built on.

If these common fundamental features were set aside, real difficulties would appear:

• No way to organise the diversity. With so many species, there would be no logical basis for sorting them into groups, and the variety would simply overwhelm any attempt at study.
• Every species would need separate study. Classification lets us examine a few representative types that stand in for their relatives; without shared features to define groups, each of the million species would have to be studied on its own.
• New animals could not be placed. A newly discovered animal is slotted into a definite, systematic position by comparing its fundamental features with known groups. Remove those features and there is nothing to compare against, so the animal cannot be placed.
• False relationships. Grouping by superficial resemblance would put unrelated animals together and split apart animals that are genuinely alike, distorting our understanding of how animals are related.

Method: The common-name trap — a case-study approach

Instead of listing the abstract consequences of dropping fundamental characters, run one concrete case through the classification process and watch it break down.

Take five animals whose common names all happen to end in the word "fish": cuttlefish, jellyfish, silverfish, dogfish and starfish. On outward appearance alone — the shared word "fish" — a classifier ignoring fundamental characters would lump all five together into one group. But checking their actual fundamental characters shatters this immediately: cuttlefish is a mollusc (soft body, shell, radula), jellyfish is diploblastic and radially symmetric (Coelenterata), silverfish is a segmented, jointed-limbed arthropod, dogfish is a true fish with a two-chambered heart and cartilaginous endoskeleton, and starfish has a water-vascular system and a calcareous endoskeleton (Echinodermata) — five entirely different phyla.

This single case study reproduces, by direct failure, everything the abstract argument predicts:

• Diversity becomes unmanageable, because there is no principled way to separate five utterly different body plans once surface naming is the only guide.
• No representative study is possible, because "fish-named animals" is not a real biological group to generalise from.
• A newly found animal named, say, "flatfish," could not be reliably placed — is it a true fish, or another homonym?
• The grouping actively misleads: it implies a close relationship (all "fish") where none exists, while separating true relatives that happen to carry different common names.

Running this one concrete trial exposes exactly the breakdown the abstract reasoning warns about, confirming it experientially rather than by assertion alone.

Conclusion: Testing classification-without-fundamental-characters against a real example shows it collapses into confusion, false grouping and an inability to place new organisms — the same result reached by reasoning about the principle directly, arrived at instead through a concrete failure case.