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Abstract: The two main approaches in interpreting the significance of non-radial fossil echinoderms (carpoids) have consistently produced the same two distinct clusters of results for over a century of investigation. Studies based on conceptual models imbued with Haeckelian precepts consider bilaterally symmetric or asymmetric morphologies of carpoids plesiomorphic for the phylum. These approaches do not find a place for carpoids within an existing phylogenetic framework for the phylum because it is assumed that they primitively lack pentaradiality. Emphasis on differences between these taxa and pentaradial echinoderms forces them outside of and downward from more crownward clades. It is crucial to examine the data supporting these supposed differences. Is it worth considering non-pentaradial echinoderms as members of a well-known group of echinoderms, the blastozoans, which already includes many secondarily-derived, non-pentaradial members? Followers of an empirical model think so, presenting an integration of paleontology, embryology, body wall homology, and image analysis that derives echinoderms from a bilaterian, archimeric larva, not bilateral adults. Unprecedented modification of a single mesocoel (hydrocoel) initiated the pentaradial adult echinoderm, most parsimoniously with five primary lobes in stem forms of each major clade within the phylum. The unique water vascular system led to rearrangement of adult axes that literally have no parallel with those of any other invertebrate, representing an iconic synapomorphy for the Echinodermata. There are few, if any, developmental or stratigraphic data defending carpoids as 'bilateral precursors'. Their free appendage is now shown to be an ambulacrum, undermining any supposition of a 'head', 'tail', or 'gill slits'. Pentaradiality is plesiomorphic for the phylum, obviating the requirement for a triradial intermediate (helicoplacoids) between carpoids and pentaradial forms. Carpoids, a subset of blastozoans, exploited motility as a feeding mode, leading to extraordinary adaptations that belie their interpretation as ancestral echinoderms. 

ABSTRACT AimThe aim of the current study is to conduct a comprehensive phylogenetic analysis of the genusArbaciato elucidate the evolution and phylogenetic relationships among all extant species and reevaluate the presence of geographic structure within species that have wide, fragmented distributions. LocationSpecimens ofArbaciawere collected from 34 localities spanning the Atlantic and Pacific Oceans, and the Mediterranean Sea. MethodsWe obtained sequences from three mitochondrial markers (COI, 16S and the control region and adjacent tRNAs) and two nuclear markers (28S and 18S; the latter ultimately excluded from the final analyses). Phylogenetic trees were constructed using maximum likelihood and Bayesian inference approaches. A time‐calibrated phylogenetic tree was inferred using a relaxed Bayesian molecular clock and three fossil calibration points. ResultsOur analysis supports the monophyly of the genusArbacia, including the speciesArbacia nigra(previously assigned to the monotypic genusTetrapygus). The new phylogenetic topology suggests an alternative biogeographic scenario of initial divergence between Atlantic and Pacific subclades occurring approximately 9 million years ago. The dispersal and subsequent diversification of the Pacific subclade to the southeast Pacific coincides with the onset of glacial and interglacial cycles in Patagonia. In the Atlantic subclade, the split betweenA. punctulataandA. lixulaoccurred 3.01–6.30 (median 3.74 million years ago), possibly associated with the strengthening of the Gulf Stream current connecting the western and eastern Atlantic. Our study also reveals significant genetic and phylogeographic structures within both Atlantic species, indicating ongoing differentiation processes between populations. Main ConclusionOur study provides valuable insights into the evolutionary history and biogeography of the genusArbaciaand highlights the complex interplay between historical climate changes and oceanic currents in shaping the distribution and diversification of echinoids in the Atlantic and Pacific Oceans. 

Abstract: Echinoderms are so highly derived compared with other deuterostomes, including their sister group, hemichordates, that comparisons of body plans are sometimes accompanied by points of view enjoying varying levels of morphological, paleontological, and especially, embryological support. No echinoderm taxon has been the subject of more contentious debate than the carpoids, a disparate assemblage of non-pentaradial, flattened echinoderms that includes the Cincta, Ctenocystoidea, Soluta, and Stylophora. Because of their unusual morphologies, the phylogenetic position and significance of carpoids concerning the origins of the Echinodermata are still being evaluated. A detailed review of carpoid research over the past century and a half reveals that the debate largely results from methodological issues employing two basic, but very different models. Conceptual models, usually imbued with Haeckelian principles, consider the absence of a single character (pentaradial symmetry) as a recapitulation of the pre-metamorphic larval stage of echinoderms, forcing unusual taxa that also lack pentaradiality down the phylum's phylogenetic tree. Such scenarios assume that first echinoderms had a bilaterian-type anterior-posterior axis. Empirical models rely on comparison of non-pentaradial early forms with a wide array of data obtained from extant and fossil echinoderms. These data support a view in which larval morphologies of echinoderms are not represented in the fossil record of echinoderms, and that pentaradial symmetry was secondarily lost in carpoids, just as it was in many other coeval types of echinoderms. 

Abstract: Several levels of the Lorraine Group (Upper Ordovician) in upstate New York (USA) have yielded low-diversity, exceptionally preserved, pyritized invertebrate assemblages dominated by the trilobite Triarthrus eatoni. Sedimentological and taphonomic features suggest dysoxic bottom-water conditions, with limited transport and rapid burial by distal turbidites. Echinoderms are extremely rare in these strata. Here we report, for the first time, the occurrence of the anomalocystitid mitrate Enoploura popei in the Konservat-Lagerstätte of Beecher's Trilobite Bed. A pyritized specimen of this stylophoran was CT-scanned and three-dimensionally reconstructed. The mitrate is laterally compressed, but its 3D-rendering provided several insights into its internal anatomy and taphonomy. The recurved position of the single feeding appendage (aulacophore) is consistent with ligament-induced, post mortem contraction. This posture and the collapse of one lateral series of cover plates indicate that the individual was probably not buried alive. Nevertheless, a portion of the distal aulacophore shows clear evidence of exceptionally preserved soft parts (ambulacral system) in between two sets of slightly open cover plates and the underlying ossicles. One of the most intriguing features of this specimen is its close association with a sinuous, elongated, pyritized trace fossil, which enters the stylophoran through the mouth and disappears into the proximal aulacophore. In marked contrast with other skeletal parts of the specimen (theca and distal part of the aulacophore), the proximal rings of the aulacophore are heavily disrupted and disarticulated. Proximal rings are usually decay-resistant skeletal regions in stylophorans. Therefore, close association of this disrupted region with a trace fossil penetrating it suggests the action of an unknown infaunal scavenger. Location of this trace suggests targeting during early decay of the large muscular proximal aulacophore. 

Forty-three species, and five indeterminate taxa of Florida Neogene echinoids are discussed and their geographic and stratigraphic distributions provided. These include 16 species documented from the Pleistocene, 20 from the Pliocene, and 12 from the Miocene. Eight new species are described: Rhyncholampas meansi n. sp. from the Pleistocene; Fernandezaster whisleri n. sp., Genocidaris oyeni n. sp., and Lovenia kerneri n. sp. from the Pliocene; and Clypeaster petersonorum n. sp., Gagaria hunterae n. sp., Brissopsis hoffmani n. sp., and Abertella carlsoni n. sp. from the Miocene. Additionally, we herein recognize Abertella floridana, from the Sopchoppy Limestone, as a species distinct from Abertella aberti, and provide the first documentation of Echinolampas lycopersicus, Rhyncholampas sabistonensis, and Arbia aldrichi from the fossil record of Florida. We update the taxonomy for all referred species and their known distributions. This document is intended to be a compilation of the entire Neogene echinoid record from Florida, which is now understood to have the most speciose and diverse assemblage of Neogene echinoids in the eastern United States.