A blastoporal organizer in a ctenophore

Animal culture A closed life cycle of M. leidyi based on cydippid reproduction has been established in the laboratory. The animals used to establish the culture were originally collected at the Kristineberg Marine Research Station. Twenty to 40 individuals were maintained in 3-l Kreisel tanks at 17–19 °C in 27.5 ppt artificial seawater (ASW) (Red Sea Salt, Red Sea Fish Pharm), under a 19–5 light–dark cycle and fed once daily with Brachionus plicatilis (Rotifera). Feeding was performed manually using a Pasteur pipette by adding 3 drops of a concentrated rotifer suspension (100,000–150,000 rotifers per ml) per 3-l tank. Water in the Kreisel tanks was completely changed manually once every 2 weeks. Rotifers were fed with a commercial concentrated microalgae solution (RGcomplete, Reef Nutrition) and cultured according to a previously described protocol 15 . For embryo collection, 10–20 cydippids (0.5–0.8 cm in size) were transferred into 200–250 ml beakers before the dark period of the light–dark cycle. Spawning occurred synchronously about 2–2.25 h after the start of the next light cycle. More than 90% of embryos (up to about 99%) developed synchronously. A small fraction of embryos lagged behind by one cleavage division at early stages; however, this difference was no longer detectable by the gastrula stage. After spawning, animals were returned to 3-l Kreisel tanks. Under these conditions, animals spawned daily. …