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