Extended pre-feeding period in planktotrophic larvae of the bathyal echinoidAspidodiadema Jacobyi

Larvae of the deep-sea echinoid Aspidodiadema jacobyi Agassiz develop from opaqueeggs 98 µn in diameter. As in lecithotrophic echinoderm larvae originating from largeeggs, mesenchyme cells fill the blastocoel during the blastula stage. Unlike other planktotrophicechinoderm larvae, the mouth does not open until 21 days after fertilization,approximately two weeks into the echinopluteus stage. Despite their small size, larvae ofA. jacobyi can survive for up to eight weeks, apparently on yolk reserves, before becomingobligately planktotrophic. This nutritional flexibility may be an adaptation to patchy foodresources in the deep sea.