Experiments with larvae of Ophelia bicornis Savigny have shown that they metamorphose most readily in sand from their natural habitat and with hesitancy or not at all in sands from other sources. Their natural sand consists largely of smooth rounded grains of quartz, very uniform in size; sands of smaller and more angular grains are unfavourable to settlement and metamorphosis. It appears that size and shape of the sand grains, or perhaps, more likely, the sizes and shapes of the interstices among the grains, perceived probably by the tactile sense, is the main stimulus to metamorphosis. Chemical substances dissolving out of the sands do not seem to be responsible for this.

There is a period of time, amounting under favourable conditions to several weeks, during which an Ophelia larva is able to settle and metamorphose as soon as it comes into contact with a substratum suitable for adult life.

The ability of the larvae to distinguish bottom deposits suitable for adult life from those which are unsuitable must be of great advantage to the species in maintaining normal distribution and in conserving larvae.