760
Journal of Paleontology 91(4):755–766
Table 2. Specimens utilized in this study. SUI = University of Iowa; YPM = Yale Peabody Museum; CMCIP = Cincinnati Museum Center; AMNH = American Museum of Natural History; FMNH = Field Museum; UC = University of Chicago (note: all University of Chicago specimens are now reposited at The Field Museum); MUMG = Miami University Museum of Geology. Age and locality information are provided.
Taxon
Holocystites Hall, 1861 H. scutellus
H. cylindricus H. winchelli H. spangleri
Gomphocystites Hall, 1864 G. indianensis
Eucystis Angelin, 1878 Eucystis sp.
Osgoodicystis Frest and Strimple, 2011 in Frest et al., 2011 O. bisetti
Pustulocystis Paul, 1971 P. pentax
Pentacystis Paul, 1971 P. gibsoni P. simplex
Trematocystis Miller, 1878 T. mangiporatus
Paulicystis Paul, 1971 P. sparsus
Triamara Tillman, 1967 Triamara ventricosa
Holocystites sp. Holocystites sp.
Specimen Number
SUI 48183 YPM 19175
CMCIP 26438 SUI 48197 YPM 34764 YPM 526736
UC 5997
SUI 48164 SUI 48198 SUI 46316
AMNH 020271A MUMG-T 266 SUI 48166
FMNH 19708 CMCIP 53630
Emended diagnosis.—Large diploporitans with peristomial border plating pattern comprising two distinct circlets of plates, oral plate series and facetal series; O1–O6 surround peristome; O1 and O6 preclude O7 from the peristomial border; O7 is in contactwith the periproct. Facetal plate series distal to oral plate series. Five facetal plates lie radially and bear large facets for feeding appendages (some facets missing in taxa bearing fewer than five ambulacra). Two lateral facetal plates positioned between B and C, and the D and E ambulacra lack facets; these lateral facetal plates are lacking in Pustulocystis. Facetal plate series open, being interrupted by O7. Floor plates not incorpo- rated into oral surface, either absent or restricted to unknown erect ambulacra. Stem absent. Holdfast present at distal end of theca.
Remarks.—The plating of the oral area with the orals bordered by facetals is unique to Holocystitidae and is the primary distinguishing feature of the clade. The large facets on the facetal series connect to food grooves extending from the peri- stome without underlying floor plates. The nature of the appendages that arise from these facets remains unknown. Two scenarios are thought to be possible. First, erect ambulacra in the form of biserial ambulacral floor plates likely bearing biserial brachioles arise from the facets. Their biserial nature is sup- ported by the facet having scars for two perradially positioned plates. Further, the scars on Paulicystis where the appendages are not preserved but recumbent show them to be biserial. The second option is that these facets are for extremely stout terminal brachioles. If these are brachioles, they would be among the most robust brachioles known, being an order of magnitude larger in diameter than those typically found in blastozoans. Only material preserving these appendages will elucidate the nature of these appendages and add more data to the diagnosis. Previously proposed subfamilies within Holocystitidae include Holocystitinae Miller, 1889 (comprising Holocystites
Age
Middle Silurian Middle Silurian Middle Silurian Middle Silurian Middle Silurian Middle Silurian
Middle Silurian Middle Silurian Middle Silurian Middle Silurian
Middle Silurian Middle Silurian Middle Silurian Middle Silurian Middle Silurian
Preservation Type
Original calcite Original calcite Internal mold Original calcite Original calcite Original calcite
Original calcite Original calcite Original calcite Original calcite
Original calcite Original calcite Original calcite Original calcite Original calcite
Type
– – – – – –
Holotype Holotype Holotype Holotype
Holotype Holotype Holotype – –
and Brightonicystis), Trematocystinae Frest and Strimple, 2011 in Frest et al., 2011 (comprising Trematocystis, Pustulocystis, and Paulicystis), and Pentacystinae Frest and Strimple, 2011 in Frest et al., 2011 (comprising Pentacystis and Osgoodicystis). These subfamilies were identified by the previous phylogenetic analysis and differentiated from one another largely on the basis of numbers of facetal and oral plates. Frest et al. (2011) interpret Holocystitinae as being a paraphyletic grade with respect to Trematocystinae and Pentacystinae (Fig. 5). Furthermore, the Pentacystinae were partially designated on taphonomic features (Sheffield and Sumrall, 2015a). These subfamilies are not discussed here further pending phylogenetic analysis of the taxa in question. Triamara was separated from Holocystitidae and placed
within Aristocystitidae Neumayr, 1889, on the basis of Triamara having simple diplopores and not humatipores (Tillman, 1967). As blastozoan respiratory structures have been shown to appear more than once in evolutionary history (Sumrall and Gahn, 2006), it is not clear that using respiratory structures is valid for defining higher-level taxonomy. Triamara and Holocystitidae share some similar features concerning the peristomial border plating system, but there are also some strong deviations (see the following discussion of Triamara for further details); unfortunately, the oral areas of the studied specimens of Triamara were insufficiently preserved to be interpreted in detail. Pending better material, we retain Aristocystitidae for species of Triamara.
Genus Holocystites Hall, 1861 Figures 6.1, 6.2, 7.1, 7.6, 7.7, 7.8
Type species.—Caryocystites cylindricum Hall, 1861
Emended diagnosis.—Five ambulacra present, extending from peristome to facet scars that straddle distal edges of oral plate series and facetal plates, typically positioned on more than one
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