Laboratory Notes for BIO 1016 & 3001

Coding morphological characters for phylogenetic analysis

© Donald McClelland, 6 February 2013

Anchor-arm creatures and sucker arm-creatures are not real. They are the creation of A. D. Johnson (2005) as model organisms for morphological character coding in phylogenetic analysis. In the real world some characters are clear, and coding them is straightforward. Other characters, however, are difficult to properly code. Sometimes several attempts must be made to distinguish homologies and accurately code the morphological characters.

anchor arm Figure 1. The major anatomical features of anchor-arm creatures
(used with permission, A. D. Johnson).

Become familiar with the anatomy of anchor-arm creatures in figure 1. This will help you to properly identify characters and character states for a phylogenetic analysis. Since these are not real animals, they do not have an evolutionary history, but let’s pretend they do. Figure 2 shows seven anchor-arm creatures and one out-group sucker-arm creature. Identify the characters and character states for both kinds of organisms.

anchor arm characteristics Figure 2. One sucker-arm creature and seven anchor-arm creatures
(used with permission, A. D. Johnson).

Construct a matrix of the eight different taxa and the characters you identify and code. Use Winclada (Nixon, 2002) and TNT (Goloboff et al., 2008) to construct and analyze your matrix.


  • Goloboff, P., J. Farris, and K. Nixon. 2008. TNT: A free program for phylogenetic analysis. Cladistics 24: 774-786.
  • Johnson, A. D. 2005. “Morphological and molecular methods for creating phylogenetic trees.” Pp. 121-154, in Tested Studies for Laboratory Teaching, Volume 26 (M. A .O'Donnell, Editor). Proceedings of the 26th Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 452 pages.
  • Nixon, K. C. 2002. WinClada ver. 1.00.08. Pubished by the author, Ithaca, NY.

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Last updated 12 feb 2013 dmcc/jhw