Gibberula is a genus of minute sea snail, a marine gastropod mollusk or micromollusk in the family Cystiscidae, previously placed in the family Marginellidae, the margin shells or marginellids.[1]
(Note: Gastropod taxonomy has been in flux for many years. This is especially true currently, because of new research in molecular phylogeny. Because of all this ongoing change, different reliable sources can yield very different classifications, especially within certain poorly understood groups.)
Other genus-group names are available for small shells resembling Gibberula. These include Granula Jousseaume, 1875 and Kogomea Habe, 1951. They are distinguished from Gibberula only on the basis of smaller size and other rather tenuous conchological differentiations.
The shell of this genus is 1.5 to 10 mm in length, ovoid, stout, with a small, low spire. The outer lip is thickened but without an external varix. It is usually denticulated inside. The columella has several plaits on a thickened rim, decreasing in size towards the posterior end. The siphonal canal is distinctly notched.
The head is deeply divided in two. There are two short cephalic tentacles and two small anterior lobes. The eyes are a short distance behinde the tentacles. The mouth is provided with an extensible proboscis. The foot is only slightly longer than the shell when extended. In some species, the sole lies flat on the substrate when the animal is crawling. Others have the edge of the propodium raised, developed as parapodia which fit the head/tentacles in the manner of many tectibranchs.
The mantle does not extend over the shell during normal activity. A tongue shaped, translucent lobe may be seen on the left side in some instances. The internal mantle is usually visible through the shell. It may be brightly coloured in the smaller species with a featureless, translucent shell, and its pattern is then continued into the spire over the visceral mass. The siphon is short and inconspicuous, often bordered by a small pad.