Non-Amniote Among Vertebrates: Fish Lack Amniotic Egg

Amniotes are tetrapods characterized by amniotic eggs or equivalent structures with amnion, chorion, and allantois membranes for terrestrial reproduction. The correct answer is 4. Fish.

Correct Answer

Fish (class Actinopterygii/Chondrichthyes) are anamniotes laying aquatic eggs without protective extra-embryonic membranes, requiring external water for development and gas exchange. Amniotes evolved ~350 million years ago for land independence via shelled eggs or placentas.

Option Explanations

1. Birds (Amniote – Incorrect Choice)

Birds lay hard-shelled amniotic eggs with all key membranes (amnion for cushioning, chorion for gas exchange, allantois for waste).

2. Mammals (Amniote – Incorrect Choice)

Mammals develop homologous amniotic membranes internally via placenta (monotremes lay eggs); all share amniote traits like waterproof skin.

3. Reptiles (Amniote – Incorrect Choice)

Reptiles (including turtles, snakes, lizards) pioneered amniotic eggs with leathery shells, enabling full terrestrial reproduction.

4. Fish (Non-Amniote – Correct)

Fish eggs lack amnion/chorion/allantois, depending on gelatinous coatings and aquatic environments; they represent pre-amniote vertebrate lineage.