Definition: microscopic algae, typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist individually, or in chains or groups.
Definition: aquatic organisms that construct and inhabit simple unbranched vertical shafts with only one opening to the surface. These are primarily above-sediment filter-feeders, surface deposit-feeders, and subsurface deposit-feeders (head-down, conveyor-belt feeders)
Definition: Skeletal support provided by hydrostatic pressure from a fluid filled cavity (e.g. the coelum) surrounded by muscles. Hydrostatic pressure provides skeletal support in sea anemones, jellyfish, nematodes, annelids, echinoderms, and other groups.
Definition: 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.).