<i>Callocystites fresti</i> sp. nov., and the significance of ambulacral branching in the Callocystitidae (Echinodermata, Glyptocystitoida)

Рожнов

2016

Paleontol. J.

Species attributed to Scoliocystis Jaekel, 1899, including the type species S. pumila (Eichwald, 1860) and S. thersites Jaekel, 1899 from the Ordovician of the Leningrad Region, are reviewed. Scoliocystis sp. from the Upper Ordovician of Estonia, figured by Hecker (1964), is redescribed as Maennilocystis heckeri gen. et sp. nov. and it is attributed to the family Callocystitidae Bernard, 1895. The genus Scoliocystis is inter mediate between the families Cheirocrinidae and Echinoencrinitidae in having five periproct border plates (as in cheirocrinids), but lacking plate R5 and having a reduced oral area, as in echinoencrinitids, but is retained in the Echinoencrinitidae. The similarity of Scoliocystis to the unusual North American cheirocrinid genus Sprinkleocystis is convergent. The genus Gonocrinites Eichwald, 1840, with two species, is restored among echinoencrinitids, as having four periproct border plates, whereas Echinoencrinites sensu stricto has three. The families Echinoencrinitidae and Callocystitidae arose from cheirocrinids with closed plate circlets by the loss of plate R5 and substitution of radial:lateral for radial:radial pectinirhombs. In addition, echinoen crinitids are characterized by a reduced oral area, whereas in callocystitids, the recumbent ambulacra are extensive. Scoliocystis is a stem group genus to Echinoencrinitidae plus Callocystitidae. Several glyptocysti toid genera independently developed advanced pectinirhombs.

Section: Gonocrinites Angulosusmentioning

confidence: 99%

Section: Systematic Palaeontologymentioning

confidence: 99%

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Revision of Scoliocystis (Rhombifera: Echinoencrinitidae) and related cystoid genera

Рожнов

2016

Paleontol. J.

“…Thereafter all five ambulacra have brachioles that alternate regularly. This ‘B D different’ pattern of primary brachioles is plesiomorphic in callocystitids, being present in all glyptocystitoids with five ambulacra, as far as is known (Paul, ). The ambulacra of Tetracystis are typically long, reaching the basal plate circlet or the stem in adult individuals and unbranched.…”

Section: Introductionmentioning

confidence: 96%

“…Glyptocystitoids are characterized by: a distinctive stem divided into stiff distal and flexible proximal portions, the latter composed of alternating outer and inner columnals; a theca composed of 27 plates arranged in a specific manner (4 basals, symbol B plural BB, 5 infra‐laterals ILL, 5 laterals LL, 6 radials RR and 7 orals OO); the hydropore and gonopore are associated with plates O1 and O7 and lie in the CD interambulacrum. Whether one counts the plate arrangement as a single character or many is a moot point, but it gives numerous points of comparison between taxa, such as whether the plate circlets are open, modified or closed (Paul, ) and which plates surround the periproct (Fig. ).…”

Section: Introductionmentioning

confidence: 99%

A cystoid with two left facets: the significance of Tetracystis in the evolution and classification of the Callocystitidae (Echinodermata, Glyptocystitoida)

2014

Geological Journal

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Revision of some North American Silurian callocystitid cystoids shows that Tetracystis Schuchert has the first two brachioles to the left in ambulacra B and D (B D different pattern), whereas Troosticystis Paul and Lovenicystis Regéll have only the first brachiole to the left in all four ambulacra (B–E the same pattern). ‘Apiocystites’ elegans Hall is transferred to Tetracystis because it has the B D different pattern. Lovenicystis kopfi sp. nov. is characterized by four short ambulacra. Salirocystis gen. nov. has the B D different pattern and two hydropores. All callocystitids that lack ambulacrum A are assigned to a new subfamily, the Tetracystinae; those with five ambulacra are referred to informally as ‘lepadocystines’. The previously recognized subfamily Callocystitinae is reduced in rank to a tribe within the ‘lepadocystines’. Preliminary character analysis suggests that the loss of ambulacrum A was the most significant evolutionary event within the family Callocystitidae, but has been overlooked in taxonomy. Character analysis also shows that all ‘lepadocystines’ had the B D different pattern of primary brachioles, which is retained in four tetracystine genera, Lepocrinites Conrad, Sphaerocystites Hall, Tetracystis and Salirocystis. Since Salirocystis has the plesiomorphic B D different pattern plus the apomorphic double hydropore, one cannot define a monophyletic taxon characterized by the B–E the same pattern plus one characterized by a double hydropore. Both alternatives are equally parsimonious. Here a new monophyletic tribe Lipsanocystini is defined characterized by a double hydropore. The B–E the same pattern evolved independently twice. Among current characters the loss of ambulacrum A, development of the B–E the same pattern and development of two hydropores are the most significant evolutionary events. Number of periproct border plates, length and structure of ambulacra are less significant. Copyright © 2014 John Wiley & Sons, Ltd.

Testing for homologies in the axial skeleton of primitive echinoderms

2017

J. Paleontol.

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Abstract.-The extraxial axial theory is used to investigate homology of ambulacral and oral plating because it predicts terminal branching and terminal addition of plates in the axial skeleton, although exceptions to the former may occur in some Paleozoic echinoderms. The variety of morphological designs and anomalous individuals also provide tests of plate homology. Homology of ambulacra is generally accepted, with the hydropore and/or single gonopore in Carpenter's CD interray. In the 2-1-2 ambulacral pattern the unbranched ambulacrum is always in Carpenter's A ray. All ambulacral morphology requires just three instructions: 'grow,' 'branch,' and 'stop.' The range of variation in echinoderms with fewer than five ambulacra implies that both the 'branch' and 'stop' instructions acted independently in all five rays. Numbers of ambulacra may or may not correlate with numbers of orals. Two basic patterns of 'cystoid' oral plating occur; with a single radial (circum-oral, CO) plate from each ambulacrum plus a sixth in the CD interray, and with all six interradial peri-oral (PO) plates, with two in the CD interambulacrum. Five 'orals' may involve loss of PO3 or PO6. Erect ambulacral structures are lost first in taphonomy and so poorly known. All ambulacral skeletal elements bear the same topological relationship to ambulacral soft tissues. Where branched ambulacra occur, the trunk or flooring plates are often modified first brachiolars or pinnulars. Both brachioles and pinnules may arise from facets developed on one or two flooring plates. Terminal addition of plates, spacing of brachioles/pinnules, and lack of musculature to open cover plates all suggest that 'cystoids' had extensions of the water vascular system in their ambulacra.