Development, Temperature Tolerance, and Settlement Preference of Embryos and Larvae of the Articulate Brachiopod Laqueus californianus.

Populations of the articulate brachiopod Laqueus californianus occur in dense single-species aggregations near the continental shelf/slope break (100-200 m) in Monterey Bay, California. The development of embryos and larvae of L. californianus has been examined by scanning electron microscopy. Fertilizable eggs are 130-140 {mu}m in diameter, and sperm are unmodified. Cleavage is holoblastic and radial. At 10{deg}C an up-swimming blastula develops by 18-h, and gastrulation occurs within 24-38 h. The embryo elongates on a new larval axis and the blastopore closes by 72 h. A trilobed articulate brachiopod larva forms by day 3-4, and a metamorphically competent larva with attachment disk is attained in 7 days. Competent larvae swim downwards. Effects of temperature on larval survival and development rate have also been examined. Larvae die within 1 day at 25{deg}C. At 20{deg}C, development appears normal but results in spontaneous abnormal settlement of larvae 5-6 days old. At 15{deg}, 10{deg}, and 5{deg}C, most larvae achieve competence in 5, 7, and 9 days, respectively. Many larvae survive for 71 days at 10{deg} and 15{deg}C. Patterns of larval settlement vary among substrates, but larvae show strong preference for shells of living conspecific adults. Settlement and metamorphosis can occur within 24 h upon exposure of larvae to substrate.