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: Diameter of the egg life stage of this organism. An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, it is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing embryo can survive on its own.
Definition: Hard framework, internal or external, which supports and protects softer parts of plant, animal or unicellular organism, and to which muscles usually attach in animals, includes skeletons (derived from Lawrence, 2005).
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.