Trunk up to 0.5 mm long, dorso-ventrally depressed (Pelagopleura oppressa). Mouth wide. Spiracles small and circular, at both sides of the rectum, far behind the long endostyle. Stomach rounded. Intestine arising from the uppermost part of the oral wall of the stomach. Rectum pear-shaped and oblique. Gonads valve-shaped, below the stomach. Tail with scattered groups of amphichordal cells, musculature moderately broad.