MPSC 2024 Prelims Paper-I · Question 61 of 100

Correct — option (4), 'Torpedo, Pristis, Hippocampus, Anabas'. Every name in the question is a genus, so the work is to place each one in its class and then find the option in which all four names sit together. Torpedo is the electric ray, Pristis the sawfish — both are cartilaginous fishes, with a skeleton of cartilage, a ventral mouth, placoid scales and no air bladder. Hippocampus is the sea horse and Anabas the climbing perch, both bony fishes with a bony endoskeleton, an operculum covering the gills and an air bladder. The two remaining names are not fishes at all: Ichthyophis is a limbless caecilian and belongs to class Amphibia, and Calotes is the garden lizard and belongs to class Reptilia. Test the options against that: option (1) puts the amphibian Ichthyophis among three fishes, option (2) puts both the amphibian and the reptile among two fishes, and option (3) puts the reptile Calotes and the amphibian Ichthyophis among two fishes. Only option (4) is free of any non-fish — all four of Torpedo, Pristis, Hippocampus and Anabas are fishes, which is the grouping the question is after, fishes being taken here as a single class (Pisces) as the older classification does. Note the finer point that the question does not turn on: under the scheme followed by NCERT, fishes are split into two classes, Chondrichthyes for Torpedo and Pristis and Osteichthyes for Hippocampus and Anabas. Even on that finer split option (4) is the only defensible choice, because it is the only set containing nothing but fishes while the other three each mix a tetrapod class into the list.

• (1)Torpedo, Pristis, Hippocampus, Ichthyophis — Three of these four are fishes, but Ichthyophis breaks the set. It is a caecilian — a burrowing, limbless amphibian of the order Gymnophiona — and the name misleads exactly as intended, since 'Ichthyo-' means fish and the animal is snake-like in appearance. It is an amphibian on every diagnostic count: a moist glandular skin without scales of the fish type, and the amphibian pattern of respiration and development. This is the commonest wrong choice in this question, because a candidate who has correctly excluded the lizard Calotes may still take a name beginning with 'Ichthyo' for a fish.
• (2)Ichthyophis, Hippocampus, Calotes, Anabas — This option gathers three different classes into one list. Hippocampus, the sea horse, and Anabas, the climbing perch, are bony fishes; Ichthyophis is an amphibian; Calotes, the garden lizard, is a reptile with a dry scaly skin, internal fertilisation and shelled eggs. No two of those three classes can be merged under any scheme of classification, so the option fails at once. It is the sort of set that catches a candidate who is grouping by habitat or body form — small, elongated, tropical — rather than by the class characters that actually decide the question.
• (3)Calotes, Pristis, Ichthyophis, Hippocampus — Here the reptile Calotes and the amphibian Ichthyophis are both mixed with two fishes, Pristis the sawfish and Hippocampus the sea horse, so the option spans three classes and cannot be the answer. It is worth noticing that it also mixes a cartilaginous fish with a bony one, so it fails on the finer classification as well as on the coarse one. Any option containing Calotes can be dismissed before any thought is given to the fishes, because the garden lizard is the one unambiguously non-aquatic animal in the whole question.

This is a question about the classes of the vertebrates and about the genus names that a syllabus uses as their standard examples. The cartilaginous fishes, Chondrichthyes, have an entirely cartilaginous endoskeleton, a mouth placed on the underside of the head, gill slits without an operculum, tough placoid scales and no air bladder, so they must swim to stay afloat; Torpedo, the electric ray, which carries electric organs, and Pristis, the sawfish, with its toothed rostrum, are the standard examples. The bony fishes, Osteichthyes, have a bony skeleton, gills covered by an operculum, cycloid or ctenoid scales and an air bladder that controls buoyancy; Hippocampus, the sea horse, and Anabas, the climbing perch that can breathe air and move over land, are the examples usually printed. Amphibia, to which Ichthyophis belongs, are the first tetrapod class, tied to water for reproduction and with a moist skin used in respiration; the caecilians are the limbless order within it. Reptilia, to which Calotes belongs, are the first fully terrestrial class, with dry scaly skin, internal fertilisation and shelled amniotic eggs. The habit the question rewards is holding a small stock of genus names with their classes attached, rather than reasoning from the animal's shape.

MPSC's science section repeatedly tests taxonomy by printing bare genus names and asking which of them share a class, an order or a phylum. The format punishes a candidate who reasons from appearance, because the paper deliberately chooses animals whose look contradicts their class: Ichthyophis is a legless amphibian that resembles a worm or an eel, Hippocampus is a fish that does not look like one, and Anabas is a fish that climbs. The method that works is to settle each name independently against a remembered list, mark it with its class, and only then read the options; a single correctly placed name is often enough to strike out two or three of them. It is also worth reading these questions with the coarse-to-fine order of the taxonomic hierarchy in mind, since a question that asks for the same class is answered differently from one that asks for the same phylum, and all six animals here belong to the one phylum Chordata.

• Torpedo is the electric ray and Pristis the sawfish; both are cartilaginous fishes with a cartilaginous endoskeleton, a ventral mouth, placoid scales and no air bladder.
• Hippocampus, the sea horse, and Anabas, the climbing perch, are bony fishes, with a bony skeleton, an operculum over the gills and an air bladder.
• Ichthyophis is a caecilian, a limbless burrowing amphibian, despite a name whose first element means fish.
• Calotes, the garden lizard, is a reptile, with dry scaly skin, internal fertilisation and shelled eggs.
• All six genera named in this question belong to the phylum Chordata, so the question can only be settled at the level of class, not phylum.

• Reading Ichthyophis as a fish because of its name; it is an amphibian, and it is the trap on which this whole question turns
• Grouping animals by habitat or body shape rather than by class characters — the sea horse and the climbing perch both look wrong for their class
• Confusing the level asked for: all six genera share a phylum, so an option can only be judged at the level of class
• Forgetting that under the finer classification the fishes are two classes, Chondrichthyes and Osteichthyes, and not one

Taxonomy questions in MPSC papers usually appear as a list of genus names with the candidate asked to identify the odd one out, the pair that shares a class, or the matching of a genus to its group. The names are drawn from a fairly small and stable stock — Scoliodon, Pristis, Torpedo, Trygon, Exocoetus, Hippocampus, Labeo, Catla, Clarias, Anabas among the fishes, and Ichthyophis, Rana, Salamandra among the amphibians, Calotes, Naja, Chelone among the reptiles — so the reliable preparation is to memorise that stock with its classes rather than to study taxonomy in the abstract. Expect at least one name in every such question to be chosen because its appearance or its name points at the wrong class.

No directly related past PYQ was found.

• practice — not a real PYQ

  Ichthyophis, which is often mistaken for a fish because of its name, belongs to which class of vertebrates ?

  • (a)Chondrichthyes
  • (b)Osteichthyes
  • (c)Amphibia
  • (d)Reptilia

  Answer(c) Amphibia — Ichthyophis is a caecilian, a limbless burrowing amphibian of the order Gymnophiona. Its name begins with a Greek element meaning fish and its body is snake-like, but it has the moist glandular skin and the amphibian life history that place it firmly outside the fishes.

• practice — not a real PYQ

  Which one of the following features is present in Osteichthyes but absent in Chondrichthyes ?

  • (a)Placoid scales
  • (b)Air bladder
  • (c)Ventral mouth
  • (d)Cartilaginous endoskeleton

  Answer(b) Air bladder — bony fishes possess an air bladder that regulates buoyancy, which cartilaginous fishes lack, so the latter must keep swimming to avoid sinking. Placoid scales, a ventrally placed mouth and a cartilaginous endoskeleton are all characters of Chondrichthyes, not of Osteichthyes.