Embryonic and larval development of the invasive biofouler Mytilopsis sallei (Récluz, 1849) (Bivalvia: Dreissenidae).
The marine dreissenid bivalve Mytilopsis sallei is a fouling organism that has invaded habitats outside its original range. Understanding its early development will be useful for early detection in the environment, for species identification in ballast water and for development of control strategies targeted at early life stages, which will help us better manage this important invader. The processes of embryogenesis, shell formation and larval development of M. sallei are described here for the first time by using light and scanning electron microscopy. Released oocytes are 64 µm in diameter. Fertilized eggs were incubated at 27±1°C. The trochophore, with an apical tuft and a prototroch, developed by 6.0±2.3 h postfertilization (hpf). At 16.5±4.2 hpf, D-shaped veligers with shell length (SL, mean±SD) of 87.3±8.2 µm appeared, each possessing a velum and a calcified shell. At 2-3 d postfertilization (dpf), the D-shaped veligers developed into umbonate larvae (SL=111.9±10.7 µm), the last obligate free-swimming veliger stage. Pediveligers (SL=232.8±37.1 µm) observed at 6-8 dpf could either swim using their velum or crawl with their foot. Pediveligers settled by secreting byssal threads and metamorphosed to plantigrades (SL=298.7±45.2 µm) 8-10 dpf. It is noteworthy that the larvae of this invasive bivalve are capable of settlement within 10 d. This is the first detailed study of early shell formation of a species of the family Dreissenidae. Shell field invagination appeared during gastrulation, secreting shell material by expanding over both sides in a saddle-shape during the trochophore stage.