Britannica
Sources used in this answer
How do bryozoans extend their lophophores after withdrawing them?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
moss animal
Eurystomella bilabiata, a moss animal from the Order Cheilostomata.
Bryozoans extend their lophophores by increasing the hydrostatic pressure of their body fluid, which forces the tentacle sheath and tentacles to emerge through the orifice.1
The specific mechanism for this eversion varies by group:
- Phylactolaemates: These organisms possess a muscular and contractile body wall that generates the necessary pressure.1
- Gymnolaemates: While their body walls are nonmuscular, they are flexible. In many species, this allows the wall to be pulled inward by associated parietal muscles, or in others, a specialized internal sac called an ascus is inflated with seawater to compress the body fluid and push the lophophore out.1
- Stenolaemates: Because their walls are rigid calcareous tubes that cannot be inflected, they utilize muscles to force body fluid from one part of the zooid to another to facilitate movement.1
When not feeding, these animals withdraw their lophophores into the coelom by inrolling the tentacle sheath, a process driven by paired retractor muscles.12