col·u·mel·la 
(kŏl′yə-mĕlə, kŏl′ə-)
(kŏl′yə-mĕlə, kŏl′ə-)n. pl. col·u·mel·lae (-mĕlē)
Any small columnlike structure in various plants and animals, often forming the central axis of development for the organism or an anatomical structure.
[Latin, diminutive of columna, column; see COLUMN.]
col′u·mellar (-mĕlər) adj.
col′u·mellate′ (-mĕlāt′) adj.