A fasciole is a thickened spiral band formed by the successive growth lines on the edges of a canal.
The term "anal fasciole" has been proposed by W.H. Dall in 1885 for the raised ring or band marking the track of the notch that forms a conspicuous feature in the sculpture of some gastropod shells. This is very prominent in turban snails (family Turbinidae). This notch is for the purpose of allowing the effete matters to escape from the anus without fouling the water going to the gills. The anal fasciole is often well-defined and can vary in size and prominence among different species.
The term "siphonal fasciole", named by Theodore Gill, bears a somewhat similar relation to the anterior end of the siphonal canal, but is generally less distinctly marked off from the rest of the surface.
The notch itself is a break or irregularity in the peristome, denoting the position of the siphon. The term "anal notch" may be used in description to distinguish it from the "siphonal notch". [1]
References edit
- ^ Dall, W. H. (1885). New or specially interesting shells of the Point Barrow Expedition. Proceedings of the United States National Museum. 7(460): 523-526.
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