Key

(from Allan Hancock Pacific expeditions vol. 1 1943)

Family Lineidae

Key to Genera

1. Lateral edges of body folded back over dorsal surface to form longitudinal groove in dorsomedian line....Diplopleura
1. Dorsal surface without median longitudinal groove....2

2. Without longitudinal cephalic grooves; caudal cirrus present....Zygeupolia
2. With longitudinal cephalic grooves....3

3. Caudal cirrus absent; proboscis sheath usually much shorter than body....4
3. Caudal cirrus present; proboscis sheath usually nearly as long as body....5

4. Body remarkably thick and massive, usually nearly cylindrical when fully extended but broad and much flattened in intestinal region when partially contracted; ocelli absent; muscular layers of body wall with reddish tinge....Euborlasia
4. Body long and slender, filiform in some species, rounded or flattened in others, very contractile; ocelli present in most species....Lineus

5. Body rather soft, usually flattened ; lateral margins not thin; not adapted for swimming; mouth small and round; proboscis sheath often much shorter than body, but proboscis very slender and much longer than body ; ocelli usually present....Micrura
5. Body firm, long and ribbonlike; much flattened in intestinal region, with very thin lateral margins and well adapted for swimming; body less contractile than in other genera; dorsoventral and diagonal muscles well developed ; mouth large and elongated in some species ; ocelli very small or absent in most species....Cerebratulus