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 den se single-species aggregations near the continental shelf/slope break (100- 200 m) in Monterey Bay, California. The development of embryos and larvae o f L, californianus has been examined by scanning electron microscopy. Ferti lizable eggs are 130-140 mu m in diameter, and sperm are unmodified. Cleava ge is holoblastic and radial. At 10 degrees C an up-swimming blastula devel ops by 18-h, and gastrulation occurs within 24-38 h. The embryo elongates o n a new larval axis and the blastopore closes by 72 h. A trilobed articulat e 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 be en examined. Larvae die within 1 day at 25 degrees C. At 20 degrees C, deve lopment appears normal but results in spontaneous abnormal settlement of la rvae 5-6 days old. At 15 degrees, 10 degrees, and 5 degrees C, most larvae achieve competence in 5, 7, and 9 days, respectively. Many larvae survive f or 71 days at 10 degrees and 15 degrees C. Patterns of larval settlement vary among substrates, but larvae show strong preference for shells of living conspecific adults. Settlement and metamor phosis can occur within 24 h upon exposure of larvae to substrate.