New model for the formation and function of sagittocysts: Symsagittifera corsicae n. sp. (Acoela)

This study is focused on the formation and function of sagittocysts, which are secretions typical of members of the acoel family Sagittiferidae. The needle‐shaped sagittocysts are produced in specialized gland cells (sagittocytes) whose distal necks are often surrounded by muscle mantles. Contraction of the muscle mantle ejects the sagittocyst. We establish a model for the development of sagittocytes and muscle mantles out of the stem cell pool of the new acoel species Symsagittifera corsicae. We used various techniques, especially interference and phase‐contrast microscopy of living specimens as well as labeling of the body‐wall musculature, for species characterization. In addition to the morphological features, we provide the third complete sequence of the 18S rDNA gene in the family Sagittiferidae.