Bacteria of the genus Wolbachia are bacteria that live within the cells of their hosts. They infect a wide range of arthropods (insects, arachnids, and crustaceans) and some nematodes (parasitic roundworms). Scientists estimate that Wolbachia exist in between seventeen percent and seventy-six percent of arthropods and nematodes. The frequency of the bacteria makes them one of the most widespread parasites. In general, they are divided into five groups, from A to E, depending of the species of their host. They cause diverse reproductive and developmental changes on their numerous invertebrate hosts. Several mechanisms, like the feminization of the embryo's sexual characters, are involved in those processes. To reproduce, Wolbachia often exploit their hosts' reproductive processes. Additionally, they are symbiotic in that they are necessary for the normal development of organisms in some species

Oviraptor philoceratops was a small bird-like dinosaur that lived about seventy-five million years ago, during the late Cretaceous period. In 1923, George Olsen of the American Museum of Natural History (AMNH) in New York City, New York, discovered the first Oviraptor fossilized skeleton on top of a dinosaur egg nest in the Gobi Desert, Mongolia. Because of the close proximity of dinosaur and nest, when Henry Fairfield Osborn president of the AMNH published on the discovery, he assumed that the Oviraptor had died attempting to steal the eggs. However, since the initial discovery, more Oviraptor adults, eggs, and a well-preserved embryo fossil have confirmed that Oviraptors were parents who sat on their nests, a behavior called brooding common among birds. The fossils of Oviraptor philoceratops, from eggs and embryos to adults, provide evidence about dinosaur growth, development, and reproductive behaviors.

The Southern Gastric-Brooding Frog (Rheobatrachus silus) was an aquatic frog that lived in south-east Australia. In 2002, the International Union for Conservation of Nature Red List declared the frog extinct, although no wild specimens had been reported since 1981. As the common name alludes to, the R. silus was a gastric-brooder, meaning that the female's eggs developed inside of her stomach. Weeks after ingestion, juvenile frogs escape through the mother's mouth. Because no other observed species performs this reproductive behavior, in the early twenty-first century R. silus became a target of the de-extinction movement that aims to resurrect extinct species. Researchers studied this frog's reproductive behavior and how the eggs and embryos escape digestion. Some scientists claimed that resurrecting this frog could result in future medical applications related to digestion and to reprogramming organ function, as during pregnancy, R. silus's stomach physiologically functioned as a uterus.

Dictyostelium discoideum is a cellular slime mold that serves as an important model organism in a variety of fields. Cellular slime molds have an unusual life cycle. They exist as separate amoebae, but after consuming all the bacteria in their area they proceed to stream together to form a multicellular organism. These features make it a valuable tool for studying developmental processes and also for investigating the evolution of multicellularity. Long thought to be a type of fungus, it has recently been shown that slime molds in fact bear no relation to fungi. Rather they form the monophyletic Mycetozoa, which consists of three distinct groups: plasmodial slime molds; cellular slime molds; and the Protostelia, all of which are structurally similar and consist of a fruiting body supported by a stalk. The cellular slime molds are characterized by a life cycle that includes periods of both multicellularity and unicellularity.