Fig. 2 in Reply to Bauer et al 2022

Fig. 2. Oral plating in holocystitids (A, C), sphaeronitids (B), and parasphaeronitids (D) to show similarities and differences. In holocystitids the mouth (M) is surrounded by six interradial plates (periorals, 1–6), two in the CD interambulacrum which share the hydropore (H) and one each in the other interambulacra. A seventh perioral (PO7) occurs in the CD interambulacrum and borders the anus (An). In Pustulocystis pentax Paul, 1971 (A) the perioral circlet is surrounded by five radial (circumoral) plates each of which bears a single ambulacral facet. In Eucystis angelini Regnéll, 1945 (B) six plates border the mouth, five of which are radial, bear ambulacral facets and are interpreted as circumorals, the sixth lies in the CD interradius and is interpreted as plate PO7. A small additional plate (CO7) shares the gonopore (G) with CO1. In Trematocystis globosus (Miller, 1878) (C) the perioral circlet is identical to that of Pustulocystis pentax, but is surrounded by seven circumorals (CO1–CO5, X1, X2) plus PO7. Trematocystis globosus also lacks the facet for ambulacrum A. In Pachycystis norvegica Bockelie, 1984 (D), as in Eucystis, the mouth frame of six periorals is absent, but the eight other plates are identical to those in the circumoral circlet of Trematocystis, including PO7. Pachycystis norvegica also lacks the facet in ambulacrum A. Two points are important. In holocystitids two plate circlets surround the mouth which, whatever they are called, cannot be homologous because they occur in the same individual. Secondly, if one accepts the plate homologies suggested here, the solitary interradial oral of sphaeronitids and parasphaeronitids must be PO7, not CO6 as it was originally labelled (Paul 1973: fig. 10B). A–E, ambulacra A–E; Pep, periproct (anal) border; Pes, peristome (mouth) border. Not to scale.