Egg (biology) - Eggs of Different Animal Groups

Eggs of Different Animal Groups

Several major groups of animals typically have readily distinguishable eggs.

Overview of eggs from various animals
Class Types of eggs Development
Jawless fish Mesolecithal eggs, especially large in hagfish Larval stage in lampreys, direct development in hagfish.
Cartilaginous fish Macrolecithal eggs with egg capsule Direct development, vivipary in some species
Bony fish Macrolecital eggs, small to medium size, large eggs in the coelacanth Larval stage, ovovivipary in some species.
Amphibians Medium sized mesolecithal eggs in all species. Tadpole stage, direct development in some species.
Reptiles Large macrolecithal eggs, develop independent of water. Direct development, some ovoviviparious
Birds Large to very large macrolecithal eggs in all species, develop independent of water. The young more or less fully developed, no distinct larval stage.
Mammals Macrolecithal eggs in monotremes and marsupials, extreme microlecithal eggs in placental mammals. Young little developed with indistinct larval stage in monotremes and marsupials, direct development in placentals.

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