This is a very slender little fish, particularly so behind the vent, males being about 35 times as long as they are deep and females about 30 times. The head occupies one-eighth to one-ninth [page 313] of the total length (in the trumpetfish it is nearly one-third); the snout is tubelike, blunt ended, with the small toothless mouth at its tip. The gill openings are very small. The body is hexagonal in cross section in front of the vent but is four-sided behind the dorsal fin and it is clothed in an armor of bony plates connected in rings, of which there are 18 to 20 in front of the vent and 36 to 42 behind the latter. The abdomen of the male is wider just back of the vent than elsewhere, with two lateral flaps that meet along the midline to form the so-called "marsupial" or brood pouch. The female lacks these. The dorsal fin (35 to 41 rays and 5 or 6 times as long as it is high) covers 4 or 5 of the bony rings in front of the vent and as many behind it. The caudal fin is rounded, its middle rays the longest. The anal is very small, close behind the vent; the pectorals are of moderate size; there are no ventral fins.