MacCoil.GIF MacCoil

Mollusc Shell Coiling Visualization

(Ver 1.07b Dec. 9, 1996, A.Richard Palmer; download)


MacCoil allows students to visualize the effects of changing different geometric coiling parameters on the shapes of mollusc shells. A 'point-and'click' interface allows parameters to be manipulated individually (see illustration below). Alternatively, pre-defined parameter combinations may be selected from the "Shells" menu to draw a variety of gastropod and bivalve shell forms.

The drawing algorithm also may help students better visualize how shells actually grow: 'new' shell is added progressively to previous apertures. MacCoil runs best on machines with a math coprocessor, but will still run on almost any version of Mac (including Plus and SE).

Unfortunately, MacCoil does not allow you to save new parameter combinations at present (a formal Macintosh interface for this ability involves more work than you might think). However, you may submit your favorite new parameter combitations (along with the taxon name and order/suborder membership) and I can easily add it to the list of items in the "shells" menu.

MacCoil screen.GIF

Explanation of parameters:

Shell Models

The geometric model used by MacCoil (from Illert, 1982*) is under-parameterized (e.g., it cannot generate planispiral shells). Nonetheless it can reproduce a wide variety of shell shapes and allows students to see how small changes in geometric parameters can have rather large effects on overall shell shape.

Those interested in learning more about the variety of geometric models that have been developed to describe mollusc shell coiling should see the article by Stone (1996)**. Stone provides a comprehensive overview, and a discussion of the differences among models, in a nice historical framework.

* Illert, C. 1982. The mathematics of gnomonic seashells. Mathematical Bioscience 63:21-56.
** Stone, J.R. 1996. The evolution of ideas: A phylogeny of shell models American Naturalist 148:904-929.


MacCoil is a Freeware program. It may be distributed free of charge for non-commercial, educational use only.

MacCoil may not be sold or bundled with other software/hardware without expressed written consent of the copyright holder:

A. Richard Palmer
Department of Biological Sciences
University of Alberta
Edmonton, AB T6G 2E9

Phone: (403) 492-3633
E-mail: ARP email


You may download a fully functional freeware version of MacCoil (ver. 1.07b; Dec. 9, 1996; download size is 34K). This file is in a Macintosh self-extracting archive coded in BinHex 4.0 format. Mac web-browsers should automatically convert the BinHex file to the self-extracting archive. Please read the notes regarding SOFTWARE DISTRIBUTION.

A.R. Palmer Home Page

Program and WWW page copyright 1997-2003 by A. Richard Palmer. All rights reserved.
(revised May 26, 2003)

have come this way in search of coiling relief since Jan. 1, 1997