si·phun·cle 
(sīfŭng′kəl)
(sīfŭng′kəl)n.
A tubelike structure in the body of a shelled cephalopod, such as a nautilus, extending through each chamber of the shell.
[Latin sīphunculus, diminutive of sīphō, sīphōn-, siphon; see SIPHON.]
si·phuncu·lar (-kyə-lər), si·phuncu·late (-lĭt) adj.