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The rhizocephalan Sacculina shiinoi sp. nov. parasitizes three species of Upogebia in Japan. It is described morphologically and compared with another Upogebia parasite, Sacculina upogebiae Shiino, 1943 from Japan and Korea. These two species are the only sacculinids that parasitize mud shrimps. DNA analyses clearly show the two species to be separate and not closely related. The cuticle differs in being provided with close-set, branched, and spiny excrescences in S. shiinoi, while it lacks excrescences, but forms small scales in S. upogebiae. In S. upogebiae, the bulbous sperm-producing part and the narrow receptacle duct are separated by a compartmentalized mid portion, which is missing in S. shiinoi. A ridge, having a thickened, fluffy cuticle with a U-shaped course, passes across the visceral mass between the two receptacle openings in S. shiinoi. Such a structure has never been described in other rhizocephalans, and its function is uncertain. [ABSTRACT FROM AUTHOR]

The intertidal Bivalvia Barrimysia siphonosomae(Montacutidae) and Pseudopythina ochetostomae(Kelliidae) live commensally with Siphonosoma cumanense(Sipuncula) and Ochetostoma erythrogrammon(Echiura), respectively. Both bivalves are hermaphrodites although males and females may occur. Paired, pouch-shaped seminal receptacles are located in the suprabranchial chamber near the genital opening of both species. The interior of the receptacles of sexually mature individuals contains numerous non-epithelial cells separated by narrow spaces that serve as a depot for sperm cells. Specimens of both species produce two sperm morphotypes. Euspermatozoa are oblong with elongate conical acrosomes, and a middlepiece consisting of about eight long mitochondria spirally arranged to form a sheath surrounding the basis of the flagellum. The paraspermatozoa are vermiform, about 4 µm broad and longer (up to 240 µm) in B. siphonosomaethan in P. ochetostomae(ca 150 µm). The anterior, bullet-shaped, 4.5- or 3.0-µm-long acrosome is located above an elongate, 4- to 6-µm-long subcylindrical nucleus. Adjacent to the nucleus occurs a bundle of approximately 25 (B. siphonosomae) or ca 10 (P. ochetostomae) flagella. The cytoplasm of the sperm body contains spherical lipid droplets, glycogen deposits and numerous membrane-bound spindle- to rod-shaped electron-dense granules. It is presumed that both sperm types aggregate to form spermatozeugmata. The presence of a combination of almost identical and highly specialised euspermatozoa and paraspermatozoa in species of the two genera qualifies these structures as strong synapomorphies. Pseudopythina, as presently defined, is considered paraphyletic.