Pleurocystitid echinoderms are known to have consistent plating in the theca or body. However, many specimens with aberrant plating are known among glyptocystitoids (Glyptocystella, Hadrocystis, Tyrridiocystis, and so on) as well as the new Ordovician species Pleurocystites? scylla, described here from the Benbolt Formation near Thorn Hill, Tennessee, USA. The presence of an extra plate in the holotype of P? scylla is most likely teratological. While teratology is often misconstrued as parasitism and pathology, it is easily recognized among glyptocystitoid rhombiferans because of the conservative nature of plate arrangements found in these taxa. Teratologic features in stemmed echinoderm thecae appear only to alter suture positioning and not significantly change the thecal shape or diminish the diagnosability of a specimen taxonomically.

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A new genus and species of carneyellid edrioasteroid, Spiracarneyella florencei n. gen. n. sp., is described from the Upper Ordovician (Kaitian) Point Pleasant Formation of northern Kentucky and southern Ohio. Spiracarneyella n. gen. is characterized by having all five ambulacra curving clockwise around the theca, having small node-bearing interambulacral plates in the distal interambulacra, and having the periproct placement slightly offset to the right side of the CD interambulacrum. The oral area of carneyellids evolved by paedomorphosis of the oral plates covering the mouth. The straight ambulacra of Cryptogoleus and the spiraling ambulacra of Spiracarneyella n. gen. evolved by paedomorphosis and peramorphosis, respectively.

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Five genera of anthaspidellid and streptosollenid demosponges are described from the Ordovician Lenoir Limestone near Lenoir City, Loudon County, Tennessee, USA including: Rhopalocoelia regularis Raymond and Okulitch, Rugocoelia loudonensis n. sp., Psarodictyum sp. (Anthaspidellidae), Allosacus pedunculatus n. sp., and Zitelella varians Raymond and Okulitch (Streptosolenidae). These findings confirm the major paleobiogeographic picture for Laurentian sponges (i.e., the differential distribution of sponge faunas along both North American margins), because none of these eastern margin species has been reported from western margin faunas. Only one genus typical of the Great Basin fauna, Rugocoelia Johns, 1994, is reported from Tennessee, but as a new species. Possible explanations are discussed for this differential distribution, mainly related to climatic constraints or sedimentary differences, preventing the free distribution of sponge species between Laurentian continental margins.

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The phylogenetic relationships of Paleozoic blastozoan echinoderms are poorly understood and many of the traditionally ascribed groups are likely polyphyletic. Diploporitans, those blastozoans with double pore (diplopore) respiratory structures, have never been placed within a rigorous phylogenetic framework, and their highly variable morphologies suggest that they do not represent a natural clade. A maximum parsimony phylogenetic analysis, spanning a wide range of diploporitan and related taxa, indicates that diplopore-bearing blastozoans are a polyphyletic grouping and, consequently, that diplopore respiratory structures have evolved more than once within the echinoderms. Constraint analyses indicate that a single diplopore-bearing clade bearing the traditionally defined Glyptosphaeritida, Sphaeronitida, Asteroblastida is less parsimonious than multiple diplopore-bearing clades inferred by the unconstrained analysis.

The external expression of hydrospires in blastoids has provided a basis for major and minor group classification in the clade for over a century. Unfortunately, the complete anatomy of the hydrospires has never been comprehensively studied. This study examined and described the internal hydrospires of six spiraculate species by digitally extracting hydrospire data from a legacy data set of serial acetate peels. Although only six models have been currently generated, hydrospire morphology is variable both within and between previously escribed spiraculate families. Hydrospires were found to possess novel characters that were incorporated into a phylogenetic analysis of the six digitally modeled species and several related species. The addition of internal morphology into the phylogenetic analysis provides further resolution between groupings of blastoids.

Hydrospires are internal structures in blastoids that primarily served a respiratory function. Historically, hydrospires have been modeled as passive-flow respiratory structures with a vertical orientation. This project constructed virtual 3D models of blastoids from legacy acetate peel collections at the Naturalis Museum in the Netherlands. Computational fluid dynamic (CFD) simulations of the blastoid models reconstructed in living position indicated that hydrospires likely were oriented horizontally when the blastoid was in feeding mode in current velocities>0.5 cm/s to 10 cm/s. In this range of current velocities, passive water flow through the hydrospires did not produce conditions optimized for efficient gas exchange. However, optimal water flow through the hydrospires could be achieved if the excurrent velocity of water exiting the hydrospire through the spiracle was approximately one-half the velocity of ambient environmental currents. Maintaining such a ratio in the dynamic current systems in which blastoids lived suggests that cilia-driven active water flow through the hydrospires is a better model for optimizing respiratory effectiveness.

Universal elemental homology (UEH) underpins recent understanding of peristomial and ambulacral elemental homology of pentaradiate echinoderms by providing a uniform set of terminology to construct phylogenetic characters. Variation in the expression of these elements provides evidence for phylogenetic relationships. Two nonhomologous sets of plates border the peristome and are associated with two nonhomologous sets of floor plates forming the ambulacral food groove. Some edrioasteroid-grade and eocrinoid-grade echinoderms have ambulacral systems formed from oral frame plates and adradial floor plates, whereas most blastozoans and crinoids bear oral plates and abradial floor plates. These plates are expressed in a variety of ways among echinoderms, but nearly all can be reconciled with the underlying model. Arguments against UEH are methodologically flawed and confuse many terms and interpretations.

The Holocystites Fauna is an enigmatic group of North American diploporitans that presents a rare window into unusual middle Silurian echinoderm communities. Multiple systematic revisions have subdivided holocystitids on the basis of presumed differences in oral area plating and respiratory structures. However, these differences were based on a fundamental misunderstanding of the homologous elements of the oral area and the taphonomic process; taphonomic disarticulation of the oral area formed the basis for the erection of Pentacystis and Osgoodicystis as separate genera, and Osgoodicystis is interpreted as the junior synonym of Pentacystis. Holocystitids show a conservative peristomial bordering plate pattern that is shared among all described genera. The peristome is bordered by seven interradially positioned oral plates as is typical for oral plate–bearing blastozoans. A second open circlet of facetal plates lies distal to the oral plates; five of these facetal plates bear facets for feeding appendages (lost on the A ambulacrum in some taxa), while two lateral facets (present in all taxa except Pustulocystis) do not. Holocystitid taxa show minor modifications to this basic peristomial bordering plate pattern. As thecal morphologies are highly variable within populations, taxonomic revision of holocystitids is based on modifications of the plating of the oral area.

Two new kirkocystid mitrate stylophorans (Echinodermata, Homalozoa) and a new possible solute (Echinodermata, Homalozoa) are described from the Early Ordovician of the western United States. The mitrates are among the earliest members of their clade to appear near the beginning of the Ordovician Radiation. Anatifopsis ninemilensis new species comes from the Ninemile Shale in central Nevada and the McKelligon Canyon Formation in west Texas. Anatifopsis fillmorensis new species comes from the middle Fillmore Formation in western Utah and a Ninemile Shale equivalent limestone bed in southern Nevada. The possible solute Drepanocystis dubius new genus new species from the lower Wah Wah Limestone in western Utah, shows unusual morphology with an elongate theca and a long arm shaped like a sickle.

Postibullinid edrioasteroids are a small clade of discoidal edrioasteroids that are locally common members of Devonian to Pennsylvanian, shallow marine, hard substrate faunas in North America and Europe. A small discoidal theca, narrow, highly elevated ambulacral cover plates, a highly elevated anal pyramid, and in many forms a posterior oral protuberance characterize this clade (Bell, 1976b; Sumrall et al., 2000). Here we describe the oldest known postibullinid, Pyrgopostibulla belli n. gen. and sp., a species that differs from other postibullinids by having a well-developed pedunculate zone and a complex, five-plate pattern of ambulacral cover plates. A dense population of these edrioasteroids preserved at a single stratigraphic horizon provides a census sample of individuals that were killed as a part of a final and abrupt burial pulse on this Lower Devonian hardground (Cornell et al., 2003). As such, this case study provides insight into the ontogeny and colonization strategies of isorophinid edrioasteroids.

A large, edrioasteroid-bearing hardground surface from the base of the Bellevue Member of the Grant Lake Formation near Maysville, Mason County, Kentucky is described. Four species are represented including Streptaster vorticellatus (Hall), Carneyella ulrichi Bassler and Shideler, Carneyella pilea (Hall), and Curvitriordo stecki n. sp. Specimens of S. vorticellatus and C. pilea add little to the known morphologies of these species. However, prior to this study C. ulrichi was known from the unique holotype, and Curvitriordo stecki n. sp. adds greatly to out understanding of Curvitriordo which was previously known from two species comprising three poorly preserved specimens. Curvitriordo stecki shows a bimodal size frequency distribution suggesting seasonal breeding whereas Carneyella ulrichi shows a left skewed size frequency suggesting low juvenile mortality. Streptaster vorticellatus shows a tight unimodal size frequency distribution suggestive of a single spat fall accumulation.

Maennilia estonica Rozhnov and Jefferies was first described as a stem-chordate but restudy shows it is an unusually large homoiostelean echinoderm. Its feeding structure, an erect ambulacrum, extending exothecally from the peristomial frame plates, bears a large internal tunnel that opens directly into the body cavity. This type of feeding appendage is now recognized to be unique to homoiosteles. It bears no evidence for water vascular system impressions adjacent to its food groove. The theca has poorly developed marginal plates and a narrow rim that, in contrast to some other homoiosteles, does not extend over either lower or upper thecal face. Maennilia appears to have inhabited the deeper portions of a near-shore environment in limey muds adjacent to a linear zone of bryozoan and microbial bioherms.

A new genus and species of edrioasteroid grade echinoderm, Kailidiscus chinensis, is described from the Kaili Biota of the basal lower Middle Cambrian Kaili Formation from Guizhou Province, China. This echinoderm has a strong resemblance to isorophid edrioasteroids, bearing a well-developed peripheral rim, long curved ambulacra, and slightly imbricate interambulacral plating at maturity. However, the presence of pore-bearing, double biserial floor plates, tiered cover plates, lack of radially positioned oral frame plates, and unincorporated hydropore/gonopore are unknown in isorophids. Many of these features bear strong resemblance to eocrinoids and helicoplacoids, attesting to the plesiomorphic nature of this taxon. Despite the obvious anatomical differences, specimens of this species preserve a complete ontogeny that resembles that of isorophids. Juveniles show a discoidal theca with straight ambulacra that transitions to an inflated theca with strongly curved ambulacra with maturity.

The glyptocystitoid rhombiferan Sprinkleocystis ektopios new genus and species is described from the Middle Ordovician (Caradoc) Benbolt Formation of Tennessee. This species is characterized by having four ambulacra bearing only terminal brachioles, the absence of lateral 5, and protuberant pectinirhombs and periproct. Many of its features are considered typical of the family Cheirocrinidae whereas others are more characteristic of the Glyptocystitidae. Its small size and simple ambulacral and pectinirhomb structures suggest a paedomorphic evolutionary origin, and its thecal morphology further suggests that the validity of a separate Cheirocrinidae and Glyptocystitidae may need reevaluation.

A new, flattened, eocrinoid-grade, blastozoan echinoderm Haimacystis rozhnovi new genus and species is described from the uppermost Lower Ordovician Wah Wah Limestone of western Utah. Although apparently most similar in morphology to the rhipidocystids, Haimacystis differs in its plane of thecal flattening, lack of one-piece marginals, and ambulacral system development. A comparison of overall morphology and plane of thecal flattening is presented for flattened blastozoans. Haimacystis was a streamlined suspension feeder attached to the sea floor by a holdfast at the end of a relatively short stem and bent over in the water column in moderate currents.