Paul—Testing for homologies in echinoderms
589
Figure 7. Ambulacra and oral plating in aristocystitid diploporites. (1) Aristocystites Barrande, 1887. (2) Calix sedgwicki Rouault, 1851. (3) Glaphocystis Chauvel, 1966. (4) Lepidocalix Termier and Termier, 1950. (5) Sinocystis Reed, 1917. In aristocystitids the mouth (M) lies within a broad food groove, which extends left and right. (2) The food grooves are covered with a double biseries of cover plates. (1)In Aristocystites, a single large facet lies at each end of the food groove. (2)In Calix, both food grooves divide to give four large facets from which up to four brachioles arise. In (3) Glaphocystis,(4) Lepidocalix,and (5) Sinocystis, the four facets apparently gave rise to a single appendage. An = anus; B–E = ambulacra; CO1–CO5 = circum-oral plates; F = ambulacral facets; G = gonopore; H = hydropore; PO1–PO6 = peri-oral plates. (1) Redrawn from Parsley (1990, p. 286, fig. 2). (2) Redrawn from Chauvel (1977, p. 315, fig. a). (3) Redrawn from Chauvel (1966, pl. 4, fig. 1E). (4) Redrawn fromMakhlouf et al. (in press, fig. 6, A2). (5) Redrawn from Bather (1918, p. 535, fig. 9). Dashed plate sutures inferred.
test of Patterson (1982, 1988), which states that two supposedly homologous structures cannot be present in the same organism. I would also suggest a further test of whether the new inter- pretation improves our understanding of early echinoderm relationships. Here I would argue that it does because I can suggest new interpretations of the oral plating of the diploporite families Aristocystitidae (Fig. 7) and Parasphaeronitidae (Fig. 11), both of which have at least eight plates associated with their oral areas. As far as Kammer et al.’s (2013) types of peristomial bor-
Figure 8. Ambulacra and oral plating in the ‘eocrinoid’ Rhopalocystis. A–E = ambulacra; F = ambulacral facet (only shown in amb D). M = mouth; PO1–PO6 = peri-oral plates. Redrawn after Ubaghs (1963, fig. 7, p. 33). Note the peri-orals lack brachiole facets.
peri-orals, forming the mouth frame, and circum-orals (previously called facetal plates, Paul, 1971) (Fig. 5.5, 5.6). If one accepts this idea, then any suggested homology between circum-orals and peri-orals can be rejected on the conjunction
der systems are concerned, among ‘cystoids,’ the unique holo- cystitid diploporite Brightonicystis Paul, 1971 (Fig. 5.4) and those hemicosmitoid rhombiferans in which the oral surface is not hidden by a tegmen (Fig. 9.1, 9.2, 9.4) have oral frames in which pairs of ambulacral plates are involved. They constitute a type of oral plating at least analogous to Kammer et al.’s type A1. I would emphasize the distinction between incorporating pairs of ambulacral plates and only incorporating the first ambulacral plate into the oral frame rather more than Kammer et al. (2013) did. I agree with Kammer et al.’s (2013) types A2 and A3,
although I would point out that Paul and Donovan (2011, p. 448, fig. 14) illustrated two examples of the same rhombiferan spe-
cies, Glansicystis glans Paul (in Paul and Donovan, 2011), which fall into both groups (see Fig. 12.1, 12.2). I suspect the difference arises because the oral area retains more or less sediment, but it could also be due to changes during growth. Kammer et al.’s (2013) type A4 differs primarily from A3 by their interpretation of the oral cover plates; that is, a palate is
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