Valves smooth or minutely striated, white and fairly translucent, with concentric growth lines and traces of radiating lines. Scutum triangular with occludent margin convex or nearly straight; ridge from apex to basi-ventral umbo weak; secondary area between this ridge and occludent margin variable in breadth. Right-hand scutum with an inner umbonal tooth, sometimes rudimentary. Exceptionally a tooth on left-hand scutum. Tergum triangular to quadrangular with occludent margin convex or angular. Carina generally smooth, seldom barbed, its base ending in a fork embedded in tissue beneath the scuta. Gap between scuta and carina not as wide as in Lepas hilli. Peduncle purplish brown especially below capitulum, variable in length, sometimes several times longer than capitulum.
Mouth parts: Labrum with fine teeth on inner margin. Palpus blunt, conical, with setae on inner side and on top. Mandible with five, occasionally six, teeth and blunt lower corner, pectinate with spines. Maxilla I of the typical Lepas shape, with setae round edge and at the sides.
Cirri segments of cirri protuberant. Shorter ramus of cirrus I 3/4 the length of the longer cirri with many segments; segments with six pairs of long spines on front margin. Caudal appendage rounded, broad and one-segmented. Filamentary appendages two, seldom one, on each side of body beneath cirrus I.
Hermaphrodite. Penis annulated and very setose.
Length of capitulum in a large specimen 50 mm; length of peduncle 40 to as much as 800 mm.
Pelagic. L. anatifera is attached to floating objects, algae etc. It is the most eurythermal species of Lepas. It does not live in water with low salinity.
Distribution in the North Sea:
South to Helgoland and the Straits of Dover.
Almost cosmopolitan, especially in tropical and subtropical seas.
From tropical-subtropical seas L. anatifera is carried to temperate and even arctic areas, but it does not reproduce in seas round Scandinavia. The cypris attaches itself to floating objects while in the Gulf Stream. The Faeroe-Shetland current occasionally transports L. anatifera to the W coast of Norway and the Jutland current carries it from the North Sea to the Skagerrak and the Kattegat. Finds have thus been made along the whole coast of Norway and W coast of Jutland. It is transported by ships to the Kattegat, Belt Sea and ¸resund. It has also been recorded from the North Sea, Shetland Islands, Faeroes, Iceland, and Spitzbergen.