Campanulinidae

Campanulinidae is a taxonomic family of sessile, marine cnidarians belonging to the class Hydrozoa. These small, colonial animals are often found attached to submerged surfaces such as rocks, shells, and seaweed. The individual units within a campanulinid colony, known as zooids, are typically enclosed in a protective cup-shaped structure called a hydrotheca. This hydrotheca is often campanulate, meaning bell-shaped, which gives the family its name.

Within the Campanulinidae, the zooids are specialized for different functions. Some zooids, called polyps or hydranths, are responsible for feeding. They possess tentacles that capture small planktonic organisms. Other specialized zooids, known as gonothecae, are involved in reproduction, producing medusae or planulae, the larval stage, depending on the species' life cycle. The colonies themselves can vary in form, from encrusting sheets to branching structures.

The distribution of Campanulinidae is largely cosmopolitan, found in temperate and tropical waters worldwide. Their ecological role typically involves filtering small particles from the water column and serving as a food source for larger invertebrates and fish. While some species may be very common in certain areas, they are generally not of significant commercial or medical importance. Their study falls within the broader field of marine biology and invertebrate zoology.