ИСТИНА

Sponges are common habitats of marine ecosystems and housed diverse commensals, but the relationships between associates and host sponges are unclear. Sponge barnacles are one of common sponge-associated fauna and some species have hollow openings between shell plates or so called “windows”. These windows are covered by the specialized membrane. We examined the windows of two species of sponge-inhabiting barnacles Acasta sandwichi and Acasta crucibasis (Thoracica: Acastinae). Under SEM (scanning electron microscope) observation, many sphincter-like opening structures (about 5 μm in diameter) were distributed on the membranes. This structures may be related to symbiotic adaptions and involved in chemical mediations between the barnacles and hosts. However, when these sponge barnacles were isolated from their hosts and cultured in the aquarium, they exhibit a gradual closure of the windows (recorded by daily photos). We used CT (computerized tomography) scan to confirm the calcification starts from the margin to the center of the windows. To further examine any microbial relationships through these windows, we made paraffin sections of a decalcified A. crucibasis specimen and performed H & E (hematoxylin and eosin) and Hoechst (cell nuclei) staining. The sections of a freshly fixed Sponge barnacle specimen showed a lot of small hematoxylin stained and Hoechst stained spots around the mantle cavity, especially in the tissue behind the window membranes. These small spots disappeared when the barnacles started to close the windows. We confirmed these small spots are bacterial cells by FISH (fluorescence in-situ hybridization) analysis using bacteria RNA probe. Further studies will address the nature of these bacteria and examine whether they are present in the sponge hosts as well.