The Responses of the Larvae of Mytilus edulis L. to Light and to Gravity

Abstract

Larvae of Mytllus edulis were raised in the laboratory after artificial fertilization. Responses of the larvae to light and gravity were tested at their various stages of development not only at normal temperature (12-15[degree]C), but also at several lower and higher temperatures. There was no response by trochophores either to light or gravity. Veliger larvae before secretion of the 1st shell were temporarily photonegative and then were photo-positive for a short time after the shell was formed. During the major portion of pelagic life, however, the veligers were indifferent to light, although they exhibited a strong negative geotaxis. After formation of a pair of eyespots the animals became photoposltive. Near the time for settlement both taxes became reversed so that they were geopositive and photonegative. These responses occurred at 5-16[degree]C. At higher temperatures there was no response to light direction. Eyed veligers at .18-20[degree]C showed a reversed (positive) geotaxis in contrast to the situation at colder temperatures.