Fig. 1

Schematic of Nanomia bijuga. Anterior [58] is toward the top of the illustrations. a Colony stage of the life cycle. For clarity reasons, protective bracts were not pictured and gonodendra of only one sex are shown per palpon in older parts of the colony. Approximate length of the illustrated colony was 15 cm. The side of zooid attachment within the siphosome is defined as the ventral side of the stem [58]. b Siphosomal growth zone and anterior part of the siphosome. Sites of gonodendra formation (goc) are located at the bases of young palpons (shown here only for the most posterior palpon in each cormidium). Gonodendra mature in older cormidia further to the posterior (a). c Nectosomal growth zone with the gas filled floating organ, the pneumatophore, at the top. d Life cycle of Nanomia bijuga. 1. Egg and sperm. 2. 1.5-day-old planula. 3. 2-day-old planula with larval tentacle bud. 4. 2.5-day-old planula with forming pneumatophore and developing larval tentacle. The mouth opening of the protozooid is at the bottom. 5. 1-week-old siphonula with pneumatophore and two larval tentacles bearing larval tentilla. 6. 20-day-old siphonula with larval bract, and zooids developing on the ventral side of the protozooid. 7. Young colony with first functional nectophore and zooids present along the elongating body of the protozooid. The elongating body of the protozooid corresponds to the future stem of the polygastric stage. 8. Mature colony—polygastric stage with multiple gastrozooids. Original figure was adapted from [34]. b bract, fg female gonodendron, g gastrozooid, goc gonodendral i-cell cluster, h horn, mgo male gonophore, ne young nectophores, NGZ nectosomal growth zone, nst nectosomal stem, p palpon, pa palpacle, pn pneumatophore, SGZ siphosomal growth zone, sst siphosomal stem, t tentacle, te tentillum. a–c Modified from [59]. d Modified from [60].