ABSTRACT
Psammechinus miliaris is found in the NE Atlantic from Scandinavia to Morocco and is very abundant in intertidal habitats but can be found up to 100 m depth. This work investigates whether its depth distribution is limited by physiological restrictions of its dispersal stages in relation to pressure and temperature and compares these results with previous similar works performed with closely related shallow-water and deep-sea Echinus species. Embryos and larvae have been subjected to different combinations of temperature and pressure. According to the results, embryos can survive and develop at depths up to 500 m and the larvae have a great tolerance to temperature and pressure conditions of abyssal environments (2000 m). This shows that P. miliaris dispersal stages are able to survive pressure conditions of both shallow and deep waters, a trait probably present in the group’s common shallow-water ancestor. Previous works show that this is also the case of another shallowwater species (E. esculentus) and that the deep-sea species E. affinis requires high pressure for normal development and survival of its embryos and larvae. Therefore, unlike P. miliaris, E. affinis shows a strong adaptation to the environment in which it lives, having lost the capability to normally develop in shallow water. Further research will include Echinus species and genetic analysis in an attempt to elucidate the process of deep sea invasion and speciation in this group of echinoids.
