The word "Family Branchiostomidae" refers to a family of marine chordates that includes a group of organisms commonly known as the lancelets. These animals are small, elongated creatures with leaf-like fins that live in the sand or mud of ocean floors. There are no synonyms for this particular scientific term, as it is a specific taxonomic classification for this particular group of organisms. However, some other common names used to refer to lancelets or members of this family may include "amphioxus," "cephalochordate," or "fish-like chordate". While these terms are closely related to the scientific classification, they are not exact synonyms for "Family Branchiostomidae".