ИСТИНА

Sponges are important component in the coral reef ecosystem and host a large number of symbiotic organisms within the sponge tissue. Spongeinhabiting barnacles are classified in the subfamilies Acastinae and Bryozobiinae, also two genera Membranobalanus and Conopea in the subfamily Archaeobalaninae. They are obligatory symbionts of poriferans, alcyonaceans and antipatharians. The key objective of the present study is to examine how do the sponge barnacle larvae settle on the sponge tissue and start their symbiotic life. Similar to the other free-living barnacle species, sponge barnacles also composed of naupliar and cyprids stages in the larval cycle. The cyprids stage is specialized to settle and a process to metamorphose to juvenile and adult stages. Barnacle cyprids use its paired antennules to explore and walk on substratum searching for settlement site. We used SEM to investigate the extreme morphological diversity in the attachment disc of sponge barnacle, which include shoe-shaped, hook-shaped and spearshaped attachment discs. We are the first to use microscopy video recording how the sponge barnacles Euacasta dofleini and Membranobalanus brachialis explore and settle in their sponge host (Petrosia sp. and Spheciospongia sp. ). They display two diverging settlement process patterns (epibiotic and embedding) and the settlement and metamorphosis process are comprised six distinct phases.