The embryo is provided with ten hooks, and appears to select Lamellibranchs (Mactra) for its intermediate host.
These organisms live in cockles, oysters and other lamellibranchs and they so affect the gonads of these molluscs as to castrate and sterilize their host.
In many embryo Lamellibranchs a centro-dorsal primitive shell-gland or follicle has been detected.
In many Lamellibranchs a gland is found on the hinder surface of the foot in the mid line, which secretes a substance which sets into the form of threads - the so-called " byssus " - by means of which the animal can fix itself.
In some Lamellibranchs (Pecten, Spondylus, Pholas, Mactra, Tellina, Pectunculus, Galeomma, &c.), although cephalic eyes are generally absent, special eyes are developed on the free margin of the mantle-skirt, apparently by the modification of tentacles commonly found there.