External Tube: A built-structure inhabited by an organism and essential to its survival, but not part of its body, composed of hardened (either rigid or flexible) secretions, with or without the addition of embedded particles, with those particles either selectively collected from the environment or passively becoming glued during formation (pers. comm. Read, G.).
- [[ExternalTube|External Tube]]
- [[NonSolidCement|Non-solid; cement]]
- [[NonSolidParticlesComp|Non-solid; particles]]