Maritrema laricola sp. n. from the intestine of the glaucous-winged gull, Larus glaucescens, differs from other species in the genus in having an elongate body, small cirrus sac, and short, curved cirrus. The life cycle of the species was followed from sporocyst stage in Littorina scutulata and Littorina sitchana, to the metacercarial stage in Hemigrapsus oregonensis and H. nudus, and to the adult in natural and experimental hosts. In experimental infections of H. oregonensis, the cercariae penetrate and develop in the gills after which they migrate to the haemocoel of the crab and encyst. The metacercariae are fully developed in from 6 to 9 weeks, and similar in size and morphology to natural infections in crabs. Excystment of the metacercariae occurs in the following cultures at 40 °C: 3% pepsin plus 1% HCl, 0.85% saline, and seawater diluted 1:4. Metacercariae live for about 3 days in diluted seawater but do not produce eggs in any of the cultures. Only immature worms were recovered from mice and newly hatched chicks when they were fed the metacercariae, but mature worms were found in natural and experimental infections of the glaucous-winged gull. In a review of the genus Maritrema, the following transfers are made: Maritrema uca Sarkisian, 1957 to the genus Mecynophallus Cable, Connor, and Balling, 1960, and Maritreminoides raminellae Dery, 1958 to Pseudospelotrema Yamaguti, 1939.
