umbonal spine

Hollow, minute to large spinose projection of conchostracan carapace that may involve entire umbo; may be curved, looped, or represented as node or nipple. (Larval condition characteristic in Vertexiidae.) [Moore and McCormick, 1969].

Hollow, minute to large, curved, looped, or nodular spinose projection, sometimes involving entire umbo [McLaughlin, 1980].