Life Cycle: "Some species of Maritrema use snails as first intermediate hosts (e. g. Zeacumantus subcarinatus and Littorina scutulata), crabs as second intermediate host and gulls as the definitive host" (Ching, 1963; Martorelli, 2004).
Body flattened, leaf-like, more or less elongated oval, sometimes tongue-shaped. Anterior end usually somewhat more pointed that posterior end. Cuticle provided with minute scales over a considerable extent. Suckers small and nearly equal; the ventral sucker is situated about the middle of the body. The intestinal diverticula may be short and sac-like or more elongated and narrow, but in no case do they extend beyond the testes; the bifurcation takes pace nearer the ventral than oral sucker. The excretory system (in Maritrema gratiosum) consists of a small vesicle from which two narrow tubules run forward; in front of the intestinal bifurcation they begin to widen and bend in towards the middle line. Just in front of the pharynx they unite in the middle line, forming a wide commissure. From this a short wide branch runs forward on each side. Ovary situated immediately behind the ventral sucker, median or somewhat to the right; it has a characteristic trilobite outline, the base facing outwards and the apex median. Uterus very voluminous, occupying the greater part of the body behind ovary, but not extending in front of the latter, Ova numerous, oval, colourless on left side of body, yellow on right. Size 0.016-0.022 x 0.008-0.012 mm. Yolk-glands of limited extent, confined to a fringe along the edge of the posterior part of the body. At the level of the testes this fringe bends inwards, passing along the anterior border of testes to unite in the middle line, so that almost a complete circle is formed. Receptaeulum seminis absent. Laurer’s canal. Testes symmetrical about the middle line, a little behind the ovary; outline oval, long axis usually transverse, sometimes decidedly oblique. Vesicula seminalis large, oval, on the right side of and close to the ventral sucker, behind which it extends some distance. It is enclosed in a well-marked cirrus-pouch. This has a somewhat pear-shaped outline, narrowing in front of the vesicular seminalis. The narrow part contains short pars prostatica and passes round in front of the ventral sucker. The genital aperture is on the left of the latter, a little behind the level of its anterior border. The vagina passes up on the left side of the sucker.
Sources: Martorelli, S.R., Fredensborg, B.L., Mouritsen, K.N., and Poulin, R. 2004. Description and proposed life cycle of Maritrema novaezealandensis n. sp. (Microphallidae) parasitic in red-billed gulls, Larus novaehollandiae scopulinus, from Otago Harbor, South Island, New Zealand. Journal of Parasitology, Vol. 90, No.2, p. 272-277.
Ching, H.L. 1963. The description and life cycle of Matitrema Lacricola sp. N. (Trematoda: Microphallidae). Canadian Journal of Zoology, Vol. 41, No. 5, p. 881-888.