Fig. 1

Morphology of the cerata. a) Dorsal view of Orienthella trilineata (USNM 1408860). Inset: detail of the cerata, and b) generalized cnidosac schematic highlighting the main morphological features of the cnidosac. Abbreviations: c, ceras; cn, cnidosac; cp, cnidophage, dg, digestive gland; e, entrance (or ciliated channel in some cases); ex, exit (or pore in some cases); k, kleptocnides; m, musculature; pz, proliferation zone