Hadromerid sponges are egg layers (oviparous). However, unlike chickens for example, fertilization is external, happening outside of the female. The female releases her egg cells and the male releases his sperm cells into the sea. Fertilization occurs as the eggs and sperm have chance encounters. This means that a large proportion of hadromerid eggs might never be fertilized. Male sponges tend to spew out huge amounts of sperm, presumably to increase the chance of meet-ups with eggs. Like all sponges, hadromerids are also able to reproduce asexually. Pieces of the adult sponge can bud off and grow into new sponges.

Sponges live in every ocean on Earth, and in some freshwater as well. They have colonized incredibly diverse habitats, from the deep, cold ocean bottom to warm, tropical seas and rough, rocky shorelines battered by waves. Some sponges are tiny dots, and others large enough for a person to get inside. They also come in a shocking variety of shapes, some quite symmetrical like cups or balls, but many asymmetrical like globs, bushes, or bread crusts. Some excavate limestone, such as mollusk shells, and live inside. Sponges may live alone or fuse with other sponges into large, underwater reefs. It turns out that this variety helps explain their ability to be successful on Earth in so many habitats. Sponges are transformers; they can change their shape by moving their cells around. Their cells can even convert to other cell types to adapt their bodies to whatever habitat or conditions they find themselves.