the mother provides eggs with sufficient nutrition for their offspring to reach metamorphosis in the
absence of food. In other cases maternal provisioning is less generous and larvae need to acquire nutrition from their environment.
Feeding larvae consume unicellular algae from the phytoplankton
during their pelagic period.
Several types of thyroid hormones (THs) have been detected in
phytoplankton: at least 3 species of unicellular algae (Heyland
et al., 2006b), and one diatom species (Chaetoceras gracilis(Chino
et al., 1994)) contain thyroxine and to a lesser extent T3. Echinoid
larvae show a well documented phenotypically plastic response to
food: larvae will grow longer arms when exposed to a low-food
environment compared to control larvae (Boidron-Metairon,
1988; Hart and Strathmann, 1994). Intriguingly, exogenous thyroxine treatment has similar morphogenetic effects as algae, which