Asymmetrical—without or lacking [symmetry].
Bilateral—pertaining to the two halves of a body as symmetrical and mirror images of each other.
Binomial nomenclature—[system] of scientific nomenclature requiring two names: generic and trivial.
Blastoid—stalked [echinoderm] with bud-like [calyx] usually consisting of 13 plates; member of class Blastoidea.
Brachiopod—bivalved marine invertebrate; member of [phylum] Brachiopoda.
Brackish—a mixture of salt and fresh waters.
Burrow—a hole in the ground, [rock], wood, etc., made by certain animals for shelter or while gathering food.
Calcareous—composed of, or containing, calcium carbonate; limy.
Calcite—calcium carbonate (CaCO₃) crystallizing in a different form than [aragonite]. In shells it is translucent and more stable than aragonite.
Cambrian—the first (oldest) [period] of the [Paleozoic] era.