Abstract
A new species of rhizocephalan, Sacculina polygenea, is described and illustrated on basis of material from the Amakusa Islands, Kyushu, Japan. Although previously recorded as a locally common parasite of the littoral crab Hemigrapsus sanguineus (de Haan, 1835), it has remained undescribed. The species is compared with S. senta Boschma, 1933 and S. nigra Shiino, 1943, which parasitize the same crab. Up to 5 concentric cuticular rings surround the stalk and adjacent part of the body. Such rings have never before been observed in any species of the genus and are probably evidence that S. polygenea moults its outer cuticle up to 5 times.
