Four species of Sagitta found in Brazilian waters are redescribed in this paper. Sagitta friderici - Numerous sensory hairs and areas are regularly distributed over the epidermis. Clearly defined collarette. Formula of the buccal armature:. Caudal to total length ratio: 25.8-29.1. Seminal vesicles almost reach posterior fins and are in contact with caudal fin; with anterior spherical swelling. Elongated ovary with eggs arranged in several rows. Sagitta hispida - Head very wide in relation to body and large collarette. Formula of buccal armature: . Caudal to total length ratio: 25.0-28.5. Seminal vesicles touch posterior fins and are separated from caudal fin. Long ovary with several rows of eggs. Sagitta minima - Has a typical body shape, small head, body widened posteriorly, tail segment thin. Collarette absent. Formula of buccal armature:. As the specimens grow, the caudal to total length ratio gradually shifts from 22.7-16.6. Seminal vesicles are separated from posterior fins and touch caudal fin. Ovary short with few eggs. Sagitta tenuis - A small species, similar to Sagitta friderici but smaller. Similarly to S. friderici it has sensory hairs and areas on the body surface. Collarette small. Formula of buccal armature:. Caudal to total length ratio: 25.0-31.8. Seminal vesicles almost touch posterior fins and touch caudal fin: anterior portion of vesicles swollen. Ovary short with few large eggs, this being its principal differential character from S. friderici. The variation indicated in the formulae of the buccal armature and of caudal to total length ratio refer to specimens of different sizes.