Question

True fish possess gills and fins. Which one of the following is not true fish.
(a) Carassius
(b) Hythalamincthyes
(c) Hippocampus
(d) Lepisma

Answer 1

Hint: The organism that belongs to the largest class of the largest phylum in the animal kingdom is commonly classed as silverfish in which exchange of gases takes place through the trachea and it is the only organism in that class without wings.

Complete answer:
First jawed vertebrates and are completely aquatic and gill breathing animals are fishes. Respiration in fishes is via gills and locomotion in fishes is assisted with paired(pectoral and pelvic fins) and unpaired fins(median and caudal fins). They are mostly ammonotelic and some of them are ureotelic. In ray-finned fish(Carassius), silver crap(hythalamincthyes), and seahorse(hippocampus) exchange of gases occurs throughout gills and they have fins for locomotion but in Lepisma exchange of gases is through the trachea and have three paired legs for locomotion.

Additional information:
- The largest group of animals on the earth are present in the class Insecta which is the largest class in the phylum Arthropoda, the largest phylum in the animal kingdom.
- Organisms in this class contain six legs and wings for locomotion and the exchange of gases takes place throughout the trachea. Cockroach, housefly, and silverfish(Lepisma) are some of the examples of this class
- Fishes are cold-blooded animals that are true vertebrates and are completely aquatic animals. They are divided into two extant classes i.e, Chondrichthyes and Osteichthyes.
- Some of the examples of true fishes are Carassius(ray-finned fish), hythalamincthyes(silver crap), hippocampus(sea horse).

So, the correct answer is ‘Lepisma’.

Note:
-In the class Insecta, almost all the organisms have wings except Lepisma.
-Jawed fishes originated from the extinct class of jawless fishes ostracoderms during the Silurian period.
-Sharks, rays, and ray-finned fishes account for the bulk of living fishes.