Tetra a tall dorsal fin characterized by a short connection to the fish’s body. Additionally, tetras possess a long anal fin stretching from a position just posterior of the dorsal fin and ending on the ventral caudal peduncle, and a small, fleshy adipose fin located dorsally between the dorsal and caudal fins. This adipose fin represents the fourth unpaired fin on the fish (the four unpaired fins are the caudal fin, dorsal fin, anal fin, and adipose fin), lending to the name tetra, which is Greek for four. While this adipose fin is generally considered the distinguishing feature, some tetras (such
Avicularium shape as the autozooids. Interzooidal avicularia are wedged between autozooids but do not replace an autozooid. Adventitious avicularia are placed somewhere on the external (frontal) wall of an autozooid and are usually much smaller. The 'birds-head' avicularium (e.g. "Bugula") is elevated above the colony by a stalk (peduncle). A zooid where the operculum is modified into a very long, hair-like structure is called a vibraculum. The cylcostome family Eleidae, which convergently evolved an opercular structure during the Early Cretaceous to Paleocene, also possess avicularia-like zooids. Avicularium The avicularium (pl. avicularia) in cheilostome bryozoans is a modified, non-feeding zooid. The operculum,