Larval development of the deep-water wood boring bivalve, Xylophaga atlantica richards (Mollusca, bivalvia, pholadidae)

Abstract

Adult Xylophaga atlantica obtained from lobster pots set at a depth of 100m released gametes in the laboratory when the water temperature was raised from 4 to 9 °C. Sperm were rarely observed but spawned eggs invariably developed, suggesting internal fertilization. Mean egg diameter was 45μm; eggs were round, yellow to light brown. Larvae reared at 9 and 14°C and 31 % salinity were free swimming in 30-40 hours and 20–24 hours respectively. Swimming larvae held in tall culture vessels congregated in a horizontal band where the temperature was 11–13 °C. Straight-hinge veligers developed in 4 days and averaged 62 μm in length. The umbo veligers ranged from 150 to 255 μmin length and had a very large characteristic velum. Pediveligers appeared 50days after fertilization and averaged 280 x 268 μm in length and height, respectively. They were smooth, inequivalved, and had a well developed hinge. The foot had a tuft of long cilia at the tip. The first signs of metamorphosis were observed on the 57th day and though the larvae continued to live for 6 months they did not grow, complete their metamorphosis or penetrate wood to which they were exposed.