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SUPPLEMENTARY INFORMATION
The Carpenter system for labelling echinoderm ambulacra
The Carpenter system is illustrated in Carpenter (1884, p. 89, figure 2). The figure shows the ventral face of a crinoid with the five ambulacra labelled in clockwise order from A to E, with ambulacrum A opposite the interambulacrum containing the periproct. The periproct is thus in the interambulacrum between C and D. There is no madreporite in the figure. Hyman (1955, p. 40) described the Carpenter system similarly, writing that ambulacrum A is opposite the periproct but that if the periproct is central, ambulacrum A is that which passes through the mouth and hydropore. When the latter rule is applied to regular echinoids (Hyman 1955, figure 193C), where the periproct is central, ambulacrum A is opposite the madreporite. When the same rule is applied to irregular echinoids (Hyman 1955, figure 193D) where the periproct is not central and not in the same interambulacrum as the madreporite, the ambulacrum opposite the periproct is not ambulacrum A but is ambulacrum D, and not as Carpenter defined it. When I apply the Carpenter labels, following Hyman (1955), to the regular echinoid H. purpurescens and then identify the blastopore, the ambulacrum opposite the blastopore is ambulacrum D. This is because, as I show, the disposition of the blastopore and madreporite in H. purpurescens is the same as the disposition of the periproct and madreporite in the irregular echinoids.
The foregoing explains why it is that if I add Carpenter labels to the ambulacra of the 2+1+2 pattern, as in an edrioasteroid, and those of the 1+3+1 pattern, as in an echinoid, they would be DE+A+BC and B+CDE+A respectively. If I use the Carpenter system based on the periproct, as defined by Carpenter, assuming the blastopore to equal the periproct, the 1+3+1 pattern becomes D+EAB+C and the order of the labels is the same for the ambulacra in the two patterns, only the spacing is different.
The figures 193C and 193D in Hyman (1955) are after Cuénot (1891) and he labelled the ambulacrum opposite the madreporite as ambulacrum A. Bather (1900, pp. 20-22) discussed planes of symmetry in echinoderms and identified an M plane, through the madreporite, and recommended that the ambulacrum lying in this plane be labelled A.
Carpenter, P.H. 1884 Report upon the Crinoidea collected during the voyage of H.M.S. Challenger during the years 1873–1876. The stalked crinoids. Challenger Reports, Zoology11, 1-442.
Cuénot, L. 1891 Études morphologiques sur Echinodermes. Archiv. Biol. 11, 313-680.