Editing Radula (section)

==Radula formulae==
[[File:Ghost Slug teeth.jpg|thumb|Radula and individual tooth of the predatory [[ghost slug]], ''[[Selenochlamys ysbryda]]'']]
The number, shape, and specialized arrangement of molluscan teeth in each transverse row is consistent on a radula, and the different patterns can be used as a diagnostic characteristic to identify the species in many cases.

Each row of radular teeth consists of
* One '''central''' or median tooth (or rachidian tooth, rachis tooth)
* On each side: one or more '''lateral''' teeth
* And then beyond that: one or more '''marginal''' teeth.

This arrangement is expressed in a radular tooth formula, with the following abbreviations :
* '''R''' : designates the central tooth or the rachis tooth (in case of lack of central tooth : the zero sign '''0''')
* the lateral teeth on each side are expressed by a specific number or '''D''', in case the outer lateral tooth is dominant.
* the marginal teeth are designated by a specific number or, in case they are in a very large numbers, the infinity symbol ∞
[[Image:Radula docoglosse.JPG|thumb|right|225px|Microscopic detail of a docoglossan radula showing the denticles or teeth]]
This can be expressed in a typical formula such as:

3 + D + 2 + R + 2 + D + 3

This formula means: Across the radula there are 3 marginal teeth, 1 dominant lateral tooth, 2 lateral teeth, and one central tooth.

Another formula for describing radulae omits the use of letters and simply gives a sequence of numbers in the order marginal-lateral-rachidian-lateral-marginal, thus:

1-1-1-1-1

This particular formula, which is common to the [[scaphopod]]s, means one marginal tooth, one lateral tooth, one rachidian tooth, one lateral tooth, and one marginal tooth across the ribbon.<ref>{{cite book|title=Microscopic anatomy of invertebrates|volume=6B: Mollusca II|last1=Shimek|first1=Ronald|last2=Steiner|first2=Gerhard|chapter=Chapter 6|publisher=Wiley-Liss, Inc.|date=1997|page=748}}</ref>