Why were bryozoans once mistaken for plants?

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Eurystomella bilabiata, a moss animal from the Order Cheilostomata. — moss animal *Eurystomella bilabiata*, a moss animal from the Order Cheilostomata.

Bryozoans were historically mistaken for plants primarily due to their physical appearance and growth patterns, which often resemble moss, seaweed, or other vegetation.1

These invertebrate organisms form complex colonies composed of numerous tiny, interconnected units called zooids. Because these colonies can take on tufted, branching, or leaflike forms, early observers frequently categorized them as plants rather than animals. Some species even possess a horny texture or calcified skeletons that mimic the structure of certain corals or plant-like growths.12

It was not until the mid-18th century that these organisms were correctly identified as animals, leading to the common name "moss animal," which reflects their deceptive, plant-like outward appearance.1