Digging into boring bryozoans: systematics, diversity and phylogeny of Immergentiidae
Immergentia is an endolithic genus of ctenostome bryozoans and sole member of the Immergentiidae. Etchings of their typical spindled shaped and sometimes enantiomorphic borehole aperture in calcium carbonate substrates is accomplished by chemical dissolution. The tentacle crown of the bryozoan is essentially the only body part that extends beyond the shell surface when protruded. Previously, species were mainly described using external colony and zooidal characteristics or whole mounts, with partial histological sections conducted on a single species in 1947. Modern approaches, however, are hitherto missing. We examined, the soft body morphology of Immergentia from different locations with confocal laser scanning microscopy and the production of 3D reconstructions. In addition, zooidal characteristics such as tentacle number, size, tubulets and interzooidal distances were used to distinguish and describe species. The combination of conventional and modern methods revealed the presence of a cardiac constrictor and true stolons that can interpose between the cystid appendages, something not previously reported in immergentiids, thus necessitating an amendment of the family diagnosis. The polypide typically has eight to ten tentacles and the anus is positioned in the low or mid-lophophoral area. In addition, sequence data including the mitogenome and the nuclear ribosomal genes (18S and 28S) of four species from five locations are presented for the first time. A novel intertidal immergentiid from France is described with all species in this study having a genetic distance greater than the 3% threshold. This work supplements the rather sparse existing knowledge on Immergentiidae and proposes additional characteristics to complement existing descriptions in order to enhance future species identification.