Byssal attachment of Amusium balloti (Bernardi, 1861) (Bivalvia: Pectinidae) spat

Abstract

It has been previously reported that the saucer scallop, Amusium balloti, either lacked the ability to produce byssal threads or could do so only briefly. This present study reports our main conclusion that in the early spat stages, A. balloti does indeed secrete byssus, albeit at a time different from most scallops. We found that A. balloti first attaches by a byssus only after metamorphosis (indicated by the presence of dissoconch shell), and we found no evidence of the byssal attachment before or during early metamorphosis. By the time spat reach a shell height of 1-2 mm they secrete two or three fine byssal filaments. Byssal attachment is maintained until the spat reaches 4-5 mm, around the stage where they develop the ability to swim. This pattern is unlike that found in most other scallops that initiate byssal production and attachment before metamorphosis. We also describe post-settlement behavior of A. balloti. The newly settled postlarvae (∼200 μm shell height) crawl along the substratum by using their foot. During attachment, spat change their positions daily, moving an average of 17 mm per day. In culture, a gentle water jet and hypersaline bath (40‰) effectively detached spat, with the majority rapidly reattaching.