Studies on some digenetic trematodes from Tasmanian fishes.

The worms are slender, elongate, and ....somewhat flattened dorsoventrally. The dimensions of fifteen "in toto" mounts are 1.55-2.36 mm. long. and 0.26-0.24 mm. broad, but living specimens are narrower and one and a.half times as long as fixed specimens. The body is broadest at its middle length and tapers towards the extremities (Fig.1). It is narrowest immediately behind the crown of the rhynchus. The latter is hemispherical and bears two papillae anteriorly (Piga). (These papillae do not represent contracted tentacles as is the case in some members of the Bucephalidaes as they are seen only when the animal is extended and are not noticeable in fixed specimens). The rhynchus is notable in that it is armed with a single circlet of spindle-shaped spines, which are eighteen in number and measure 0.44 mm. long and 0.012 mm. in diameter. The circlet is interrupted in the mid-ventral line (Figs. 1-2). The body is covered hy'a thick cuticle with minute spinules 0.012 mm. long closely arranged in transverse rows. The rhynchus is free from these spinules except within the ventral break in the circlet of spines. The mouth is situated on the ventral surface, at about the middle length of the body when contracted, but at the junction of the second and last thirds of the body when extended. The genital aperture is in the mid-ventral line a short distance in front of the posterior extremity.. The excretory pore is a median transverse slit at the posterior end of the body