Ambulacral Plates Research Articles

A paedomorphic dwarf species, Gauthieria pumilio sp. nov. (Echinoidea: Phymosomatidae), from the Campanian (Late Cretaceous) of Hannover, Germany

AbstractA new phymosomatoid species, Gauthieria pumilio sp. nov., from lower Campanian (Late Cretaceous) deposits in the vicinity of Hannover, Germany, is described. This species is very close in its overall appearance (i.e. tuberculation and ambulacral plating pattern) to a few other species: Gauthieria radiata and the juvenile stages of the Santonian Gauthieria spatulifera and the Maastrichtian Gauthieria princeps, with which Gauthieria pumilio sp. nov. is accordingly closely related. However, it deviates from its relatives by a significantly smaller test diameter. Accordingly it is deviating from the general increase in size during the evolutionary lineage leading from the Turonian G. radiata via G. spatulifera to the Maastrichtian G. princeps. This lineage exemplified Cope's Rule through increasing test size. However, G. pumilio sp. nov. challenges this pattern with its dwarfing phenomenon, exhibiting a test diameter < 18 mm. It shares the ambulacral plating pattern with G. radiata and the juvenile stages of G. spatulifera and G. princeps, providing further insights into the genus's evolutionary history.

Rhombifera Barrande, 1867, and the origin of the Blastoidea (Echinodermata, Blastozoa)

Rhombifera bohemica Barrande is redescribed from Barrande’s original material and new specimens from Spain and the Czech Republic. Rhombifera had a heteromorphic proximal stem, a theca with three basals, three infralaterals and five laterals, both greatly elongated, but a reduced oral area in which five, facet-bearing radials alternate with five interradial orals which form the oral frame. The CD oral plus two others share the hydropore and gonopore. Rhombifera is the only glyptocystitoid rhombiferan with a periproct surrounded by two plates, L4 and L5, and ambulacral facets on radial not oral plates. Rhombifera was derived from echinoencrinitid glyptocystitoids, both sharing reduced oral areas with five, not six, radial plates and pectinirhombs with short oval slits. The oral areas of Rhombifera and Lysocystites are similar. In Lysocystites five facet-bearing ‘ambulacral plates’ alternate with five interradial orals forming the oral frame. Extra orals in the CD interambulacrum share the hydropore and gonopore. Lysocystites, coronates and blastoids all possess three basals, five ‘radials’, five deltoids and five homologues of blastoid lancet plates. We suggest that basals, laterals, radials and orals of glyptocystitoids are homologous with basals, radials, lancet plates and deltoids of blastoids, respectively. Rhombifera is a link between glyptocystitoid rhombiferans and blastoids.

New insights on the systematics of echinoids belonging to the family Spatangidae Gray, 1825 using a combined approach based on morphology, morphometry, and genetics

Spatangoids are probably the least resolved group within echinoids, with known topological incongruencies between phylogenies derived from molecular (very scarce) and morphological data. The present work, based on the analysis of 270 specimens of Spatangidae (Echinoidea, Spatangoida) trawled in the Sardinian seas (Western Mediterranean), allowed us to verify the constancy of some characters that we consider to be diagnostic at the genus level —such as the path of the subanal fasciole and the relationship between labrum and adjacent ambulacral plates —and to distinguish two distinct forms within the studied material. Based on morphological characters, morphometrics, and molecular analyses (sequencing of two mitochondrial markers: cytochrome c oxidase subunit1 (COI) and 16S), most of the individuals were classified as morphotype A and attributed to the species Spatangus purpureus, the most common spatangoid in the Mediterranean Sea, while a few corresponded to a different morphotype (B), genetically close to the species Spatangus raschi. Preliminary morphological analyses seemed to indicate that morphotype B specimens from Sardinia are slightly different from S. raschi and from Spatangus subinermis individuals, the second species of the family known to occur in the Mediterranean Sea. On the basis of morpho-structural observations and molecular analyses, comparing Mediterranean living forms with species from other areas (Central Eastern Atlantic, North Sea and neighboring basins, South African Sea, Philippines and Indonesian Archipelago, New Zealand, and Hawaiian Islands), the clear distinction of S. purpureus from several other species classified as Spatangus was confirmed. Based on the morphological and genetic differences, we propose to maintain the genus Spatangus including in it only the type species S. purpureus among the living species and to establish the new genus Propespatagus nov. gen. to include several other species previously classified as Spatangus. The clear distinction among different genera was also detected in fossil forms of Spatangus, Propespatagus nov. gen., and Sardospatangus (†) from the European Oligo-Miocene sedimentary rocks of Germany; the Miocene of Ukraine, Italy, and North Africa; the Plio-Pleistocene of Italy; and the Mio-Pliocene of Florida (USA). The new data can help in addressing taxonomic ambiguities within echinoids, as well as in improving species identification, and hence biodiversity assessments in the Mediterranean region.

Redefinition of the genera Opissaster Pomel, 1883 and Gregoryaster Lambert, 1907 (Order Spatangoida, Suborder Paleopneustina, Family Schizasteridae), from the Oligo-Miocene of Malta, Algeria and Sardinia

The extinct spatangoid echinoids Opissaster and Gregoryaster are apparently closely related on the basis of their overall morphology. However, the diagnostic features of these echinoids are uncertain and their systematic position has long been debated.They are distinguished mainly by the position of the apical system, the path of the peripetalous fasciole in the anterior ambulacra and the ratio between the length of anterior and posterior paired petals. However, other diagnostic features, including the arrangement of the oral test plates, have not been considered so far.The present work focuses on a revision of both genera based on the examination of the type species and of additional new material from various localities of the Oligocene and the Miocene of Malta, and the Miocene of Sardinia and Algeria.In addition to the morphological features commonly used, different aspects of the plating of some species belonging to the genera Opissater and Gregoryaster have been compared, highlighting the structural differences existing between them as we explain below.Both genera have an ethmolytic apical disc with 4 genital pores, consistently. Gregoryaster differs from Opissaster in shape and length of the labrum, which is in contact with two ambulacral plates, instead of one, along with in the course of the peripetalous fasciole in anterior interambulacra (2 and 3), and in having a vertically-elongated periproct. The ratio between the length of anterior and posterior paired petals seems unreliable for distinction at genus level. Specimens from the Lower Miocene of Sardinia, previously attributed to Gregoryaster coranguinum, are herein reassigned to a new species, Gregoryaster cabiddui sp. nov.Both genera are placed within the Family Schizasteridae, although this placement remains dubious for Gregoryaster.

Heart urchins from the depths: Corparva lyrida gen. et sp. nov. (Palaeotropidae), and new records for the southwestern Atlantic Ocean

Introduction: Sea urchins in the order Spatangoida are the most diverse group of extant echinoids. Objective: Describe a new genus and species of Spatangoida from abyssal depths, and add new records for known species. Methods: Specimens were collected during several cruises at different areas of the southwestern Atlantic Ocean (SWAO), among 37-55° S latitude at depths ranging from 55 to 3 000 m. We present morphological and ultrastructure analyses. Results: Corparva lyrida gen. et sp. nov. (Palaeotropidae) is described from the Mar del Plata Canyon on the Argentine continental slope (2 950 m depth), the first record of this family from Argentina. Corparva gen. nov. differs in having an apical system semi-ethmolytic, and labrum reaching to rear part of second adjacent ambulacral plate. We also report the northernmost distribution and deepest record for Brisaster moseleyi (38° S latitude, 2 212 m depth), the northward extension of the distribution range of Tripylus excavatus (39° S latitude, 74 m depth), and the first record of Abatus philippii and Abatus agassizii at the Burdwood Bank/MPA Namuncurá. Conclusions: The present work brings novel and updated data about the diversity and distribution of spatangoids from the SWAO, including the description of C. lyrida gen. et sp. nov., and new records of species. This shows how much remains to be known about the diversity and distribution of heart urchins in the SWAO, especially from the deep-sea.

The first record of floor plates in pinnules and the earliest record of an anitaxis in rhodocrinitid diplobathrid camerate crinoids

AbstractRestudy of Proexenocrinus inyoensis Strimple and McGinnis, 1972, shows that this earliest-known rhodocrinitid diplobathrid camerate crinoid (late Floian, Early Ordovician) expresses the only known record of ambulacral floor plates within pinnules. These pinnule floor plates are remarkably conserved plesiomorphic expressions, with anatomy similar to floor plates of some of the earliest pentaradiate echinoderms, although on a smaller scale. Proexenocrinus floor plates provide direct skeletal evidence that the general resemblance of blastozoan (eocrinoid, diploporan, rhombiferan) brachioles and crinoid pinnules is the product of homoplasy. Proexenocrinus posterior cup morphology is interpreted to include an anitaxis, a distinctive posterior interray morphology.

The heart urchin Homolampas fragilis (A. Agassiz, 1869) (Echinoidea: Echinodermata) from the Brazilian Coast

The echinoid Homolampas fragilis (A. Agassiz,1869) (Echinodermata) is recorded for the first time in the Brazilian coast from the Continental shelf of the State of Ceara. The specimens were classified based on their distinct morphological characters, including the fragile test, primary tubercles non-crenulated and with deep areoles, absent peripetalous fasciole, without aboral tubercles on the interambulacrum 5, three to four genital pores, and posterior prolongation of the labrum, not reaching the second adjacent labral plate narrow and wedge-shaped, extending to second or third ambulacral plate; only just contacting sternal ambulacral plates. This species usually inhabits tropical waters from the Caribbean Sea, Gulf of Mexico, and Florida Strait. Its bathymetry is expanded from 360–3550 to 34–3550 m deep. In the present work, we provide morphological and geographical updates on Homolampas fragilis found in the Brazilian coast.

Origin and significance of Lovén's Law in echinoderms

AbstractLovén's Law described the position of larger basicoronal ambulacral plates in echinoids. The smaller basicoronal plates form first in ontogeny. We restate Lovén's Law to describe the position of first ambulacral plates using Carpenter's ambulacra and left (L) or right (R) as: AR, BL, CR, DL, ER, with EA the pair of ambulacra both identical and adjacent. First ambulacral plates of the Cambrian edrioasteroid,Walcottidiscus, code identically. The transition from a tri-radiate 1-1-1 pattern to the 2-1-2 ambulacral pattern ofWalcottidiscusand other pentaradiate Paleozoic echinoderms results in Lovén's Law. This provides an hypothesis for the origin of Lovén's Law and predicts its widespread occurrence among echinoderm classes.The ‘BD different’ pattern of primary brachioles in pentaradiate glyptocystitoid Rhombifera results from subterminal branching of the ambulacra. The ontogenetic sequence was triradiate, then lateral ambulacra bifurcated, and finally second brachioles developed. Positions of second brachioles of pentaradiate glyptocystitoids code as AR, BL, CR, DL, ER. Other examples of Lovén's Law occur in Diploporita, Ophiuroidea, Edrioasteroidea, Edrioblastoidea, Holothuroidea, Ophiocistioidea, andBothriocidaris. Our working hypothesis is that Lovén's Law arose with pentaradiality. An objective test requires a reliable independent landmark across all classes, which does not exist currently. Our hypothesis is only parsimonious if Lovén's Law arose just once in echinoderm evolution and is widespread within the phylum. So far, both conditions appear to be met, but edrioasteroid first ambulacral cover plates commonly exhibit an alternative Lovén-like pattern of AL, BL, CR, DL, ER, with AB the identical adjacent ambulacra.UUID:http://zoobank.org/4c40d338-8bfa-4515-9037-934f3bbab153

Skeletal integrity of a marine keystone predator (Asterias rubens) threatened by ocean acidification

The current increase in atmospheric CO2 concentration induces changes in the seawater carbonate system resulting in decreased pH and calcium carbonate saturation state, a phenomenon called ocean acidification (OA). OA has long been considered as a major threat to echinoderms because their extensive endoskeleton is made of high‑magnesium calcite, one of the most soluble forms of calcium carbonate. Numerous studies addressed this question in sea urchins, but very few questioned the impact of OA on the sea star skeleton, although members of this taxon do not compensate their extracellular pH, contrary to most sea urchins. In the present study, adults of the common sea star, Asterias rubens from Kiel Fjord, a site experiencing natural acidification events exceeding pCO2 levels of 2500 μatm, were chronically exposed to different levels of simulated ocean acidification (pHT-SW 8.0, 7.4, 7.2), encompassing present and future conditions, for the duration of 109 days. Corrosion and mechanical properties of skeletal elements were studied using scanning electron microscopy, three-point bending tests as well as nanoindentation. The spines were significantly corroded at pHT-SW 7.4 and below while the ambulacral plates were only affected at pHT-SW 7.2. Nanoindentation of newly formed spines and ambulacral plates did not reveal significant CO2-induced differences in skeleton hardness or elasticity across treatments. Results of three-point bending tests revealed significantly reduced characteristic strength and fracture force of ambulacral plates from the median arm segment at pHT-SW 7.4 and below. These plates are those supporting the tube feet involved in the opening of bivalves during feeding and in the animal attachment to the substrate. Under reduced seawater pH, this might result in fracture of sea star plates during predation on mussel. The present results predict a possible impact of ocean acidification on the skeletal integrity of a marine keystone predator.

Morphology and molecular phylogeny of two new species in genus Freyastera (Asteroidea: Brisingida: Freyellidae), with a revised key to close species and ecological remarks

Freyastera (Downey, 1986) is a derived group of deep-sea starfish in the order Brisingida with 6 arms and slender ambulacral plates, whose taxonomy and phylogeny have rarely been investigated. In this research, two new species of Freyastera are reported from the northwest Pacific Ocean, both characterized by fairly long and numerous lateral spines and the presence of furrow spines. Freyastera delicatan. sp. is further distinguished from other species by having 6–8 spinelets arranged in a transverse line on each abactinal arm plate. Freyastera basketan. sp. is similar to the Atlantic species Freyastera sexradiata (Perrier, 1885), but differs from the latter by the presence of pedicellariae on the abactinal surface and number of mouth spines and lateral spines. A revised key to Freyastera and potential Freyastera spp. from the genus Freyella (Perrier, 1885) is provided. Phylogenetic analysis was conducted using available molecular data for the order Brisingida. The intraspecific and interspecific divergence within Freyastera are recognized from a COI genetic distance matrix, in which some abnormal intraspecific distances are found between the known species, which might indicate the existence of cryptic species and an underestimated diversity in the genus. A phylogenetic tree of Brisingida is constructed based on a concatenated sequence dataset of COI, 16S and H3 gene fragments. The tree supports the affinity of Freyastera and Freyella, which together form a crown clade within the order. The global distribution and in situ observations of Freyastera are discussed to provide information on their ecological characteristics and diversity.

Notes on Mississippian echinoderms from Hurdlow, Derbyshire, central England

The fossil echinoderms of the Lower Carboniferous (Mississippian) of Derbyshire remain understudied, principally due to the nature of the preservation rather than any lack of biodiversity. Echinoids and crinoids are described in float blocks of limestone from near Hurdlow, Derbyshire, which have been etched naturally after many years of being washed by weakly acidic rain. Surface detail is variable, commonly poor, but rare specimens retain enough features for tentative identification. Two species of echinoids are identified from rare disarticulated plates, namely Melonechinus? sp. (ambulacral plates) and archaeocidarid sp. (interambulacral plate); more and superior material will be necessary to confirm this division. Crinoids include a cladid brachial ossicle sp. with a distinctive sculpture; a columnal of a monobathrid camerate platycrinitid sp.; Annulocolumnus (col.) sp. cf. A. annulus Donovan, a columnal morphotaxon with an unusually broad axial canal; and Cyclocyclicus (col.) spp. This is the tenth echinoid site to be recognized from the Mississippian of the White Peak. Examination of etched float blocks provides a further method of investigation of the echinoderm fauna of this and other limestone areas.

Cryptic speciation in pan-tropical sea urchins: a case study of an edge-of-range population of Tripneustes from the Kermadec Islands

Tripneustes is one of the most abundant and ecologically significant tropical echinoids. Highly valued for its gonads, wild populations of Tripneustes are commercially exploited and cultivated stocks are a prime target for the fisheries and aquaculture industry. Here we examine Tripneustes from the Kermadec Islands, a remote chain of volcanic islands in the southwest Pacific Ocean that mark the boundary of the genus’ range, by combining morphological and genetic analyses, using two mitochondrial (COI and the Control Region), and one nuclear (bindin) marker. We show that Kermadec Tripneustes is a new species of Tripneustes. We provide a full description of this species and present an updated phylogeny of the genus. This new species, Tripneustes kermadecensis n. sp., is characterized by having ambulacral primary tubercles occurring on every fourth plate ambitally, flattened test with large peristome, one to two occluded plates for every four ambulacral plates, and complete primary series of interambulacral tubercles from peristome to apex. It appears to have split early from the main Tripneustes stock, predating even the split of the Atlantic Tripneustes lineage. Its distinction from the common T. gratilla and potential vulnerability as an isolated endemic species calls for special attention in terms of conservation.

A diverse assemblage of Permian echinoids (Echinodermata, Echinoidea) and implications for character evolution in early crown group echinoids

AbstractThe Permian is regarded as one of the most crucial intervals during echinoid evolution because crown group echinoids are first widely known from the Permian. New faunas provide important information regarding the diversity of echinoids during this significant interval as well as the morphological characterization of the earliest crown group and latest stem group echinoids. A new fauna from the Capitanian Lamar Member of the Bell Canyon Formation in the Guadalupe Mountains of West Texas comprises at least three new taxa, includingEotiaris guadalupensisThompson n. sp. an indeterminate archaeocidarid, andPronechinus? sp. All specimens represented are silicified and known from disarticulated or semiarticulated interambulacral and ambulacral plates and spines. This assemblage is one of the most diverse echinoid assemblages known from the Permian and, as such, informs the paleoecological setting in which the earliest crown group echinoids lived. This new fauna indicates that crown group echinoids occupied the same environments as stem group echinoids of the Archaeocidaridae and Proterocidaridae. Furthermore, the echinoids described herein begin to elucidate the order of character transitions that likely took place between stem group and crown group echinoids. At least one of the morphological innovations once thought to be characteristic of early crown group echinoids, crenulate tubercles, was in fact widespread in a number of stem group taxa from the Permian as well. Crenulate tubercles are reported from two taxa, and putative cidaroid style U-shaped teeth are present in the fauna. The presence of crenulate tubercles in the archaeocidarid indicates that crenulate tubercles were present in stem group echinoids, and thus the evolution of this character likely preceded the evolution of many of the synapomorphies that define the echinoid crown group.

Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia

Sadler, T., Martin, S.K. & Gallagher, S.J., February 2017. Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia. Alcheringa 41, 464–473. ISSN 0311-5518Three new species of the extinct echinoid genus Monostychia Laube, 1869 are described from Western Australia. All are from the middle Miocene Colville Sandstone of the Eucla Basin and have historically been referred to this genus without description. These new taxa differ from previously described Monostychia species in several morphological features, such as size and shape but also in the number of post-basicoronal interambulacral plates developed in the oral paired interambulacrum, a feature considered taxonomically important at both genus and species level for clypeasteroids. The number of ambulacral plates in the paired and unpaired oral regions is also considered a potentially diagnostic taxonomic feature for this genus; it is concluded that the oral ambulacral plate count, particularly that of the unpaired ambulacrum III, is at least as useful a taxonomic feature as the oral interambulacral plate count.Tony Sadler [t.sadler@student.unimelb.edu.au] and Stephen J. Gallagher [sjgall@unimelb.edu.au], School of Earth Sciences, University of Melbourne, Victoria 2010, Australia; Sarah K. Martin [sarah.martin@dmp.wa.gov.au], Geological Survey of Western Australia, Department of Mines and Petroleum, Western Australia, 6004.

Revision and re-description of Micropeltis isseli Airaghi, 1901 (Echinodermata: Echinoidea)

Re-discovery of the holotype of “Micropeltis” isseli Airaghi, 1901, in the collection of the Museo di Paleontologia (University of Genova), allowed for a re-assessment of its morphological features and revision of its systematic placement. The discovery of ambulacral plate compounding that is compatible with that of phymosomatids, in combination with its pore arrangement and tuberculation pattern, indicates that this species should be transferred to the genus Phymotaxis. Comparison with museum collections from the type area allowed for clarification of the type-locality and stratum. The specimen most likely derives from the Tortonian Marne di S. Agata Fossili beds exposed at Bocca d’Asino, northeast of Stazzano, which is in line with Airaghi’s statement in the original description (in contrast to the original plate caption). This indicates that Phymotaxis isseli is the youngest representative of the echinoid order phymosomatida known to date, extending its range to the Late Miocene.

Heterochronic evolution in the Late Cretaceous echinoid Gauthieria (Echinoidea, Phymosomatidae)

Based on representatives of the Late Cretaceous genus Gauthieria (Gauthieria radiata – Gauthieria spatulifera – Gauthieria princeps), ontogenetic trajectories within the family Phymosomatidae are described for the first time. Due to shared similarities in their ontogenetic development, an intimate evolutionary relationship must be assumed. This interpretation is most supported by analyses of the development in the ambulacral plating pattern (alternation of simple plates and compound plates), which is not commonly found among the Phymosomatoidae. This pattern, however, is present among all three species during development. The developmental trajectories of 8 further characters were included in this study (arrangement of the adapical pore pairs, number of pore pairs, pore pair numbers in ambital ambulacral plates, number of interambulacral plates, peristomal opening, apical opening diameter, test height, radial ornament of the areoles). The evolution in this lineage is characterised by several different heterochronic processes, which suggest a dissociated heterochronic evolution, indicating a developmental modularity. Additionally, the systematic treatment of G. princeps is discussed on account of the presented results.

Revision of the echinoid genus Micropedina Cotteau, 1866 and description of a new species from the upper Cenomanian of Egypt

Currently, the genus Micropedina contains seven species and a single variety, with records from the lower Upper Cretaceous of Europe (Portugal, Spain), North Africa (Algeria, Tunisia and Egypt), West Africa (Nigeria), the Middle East, India and the Americas. In Egypt, a total of five species is known to date. Based on the oblique arrangement of pore pair triads in each compound ambulacral plate, three species cannot be assigned to the genus any longer; these are ‘M.’ sphaeroides, ‘M.’ rotularis and ‘M.’ bipatellis. Using ambulacral plate compounding, two species are valid, M. olisiponensis and M. cotteaui, in addition to a variety which is here elevated to species rank, M. gongilensis, and a new species erected herein, M. simplex. Three species are described from the upper Cenomanian Galala Formation of north Wadi Qena (Northeastern Desert, Egypt) namely M. olisiponensis, M. cotteaui and M. simplex sp. nov. The palaeobiogeography, functional morphology and palaeoecology of the genus are discussed.

A Tremadocian asterozoan from Tasmania and a late Llandovery edrioasteroid from Victoria

Jell, P.A., 2014. A Tremadocian asterozoan from Tasmania and a late Llandovery edrioasteroid from Victoria. Alcheringa 38, 528–540. ISSN 0311-5518.An asterozoan, Maydena roadsidensis gen. et sp. nov., is described from the mid-Tremadocian (La1b Zone) Florentine Valley Formation in southwestern Tasmania and is the oldest known asterozoan in the world. Although only a single, largely dissociated, specimen is available, enough is preserved to recognize distinctive ambulacral plates similar to those of Archegonaster Jaekel from the Llanvirn of the Czech Republic. Reciprocodiscus transambus n. gen., n. sp. is an isorophid edrioasteroid from the uppermost late Llandovery Springfield Formation exposed in the bed of Deep Creek, near Springfield, 65 km north northwest of Melbourne. It occurs with a low-diversity trilobite fauna indicating a deepwater, subphotic environment. This edrioasteroid has in each ambulacrum a single series of floor plates that are not visible on the oral surface, indicating its isorophid affinity and retains certain apparently primitive features that are not seen in post-Cambrian edrioasteroids, such as the very large plates of the marginal circlet, plated aboral surface and ambulacral tips extending onto the marginal circlet plates.Peter A. Jell [p.jell@uq.edu.au] School of Earth Sciences, The University of Queensland, St Lucia Queensland 4072, Australia.

Absurdaster, a new genus of basal atelostomate from the Early Cretaceous of Europe and its phylogenetic position

Field work in the Lower Cretaceous of the Dolomites (Italy) has resulted in the recovery of a new genus of ‘disasteroid’ echinoid, which successively was also discovered in slightly older strata in Northern Hungary. This new genus, Absurdaster, is characterized by its highly modified, disjunct apical disc in which all genital plate except genital plate 2 are reduced or fused. The gonopores (which may be multiple) have shifted and pierce interambulacral plates. Anteriorly ambulacrum III is distinctly sunken and forms a distinct frontal notch, while the posterior end is pointed and features a small sharply defined posterior face bearing the periproct.Two new species are established: Absurdaster puezensis sp. nov. from the Upper Hauterivian to Lower Barremian Puez Formation of Northern Italy is characterized by its rudimentary ambulacral pores in the paired ambulacra, high hexagonal ambulacral plates aborally and multiple gonopores in the most adapical plates of interambulacral columns 1b and 4a. Absurdaster hungaricus sp. nov. from the Lower Hauterivian Bersek Marl Formation of Northern Hungary, in contrast, shows circumflexed ambulacral pores, low ambulacral plates, a single gonopore each in the most adapical plates of interambulacral columns 1b and 4a and a flaring posterior end, with sharp margin and invaginated periproct. In addition to those two species Collyrites meriani Ooster, 1865 from the uppermost Berriasian to basal Barremian of Switzerland is attributed to the new genus. Despite the poor knowledge on this form it seems to be distinguished from the new species by its smaller ambulacral plates and higher interambulacral/ambulacral plate ratio.Phylogenetic analyses based on previous work by Barras (2007) and Saucède et al. (2007) indicate that the new genus is a highly derived stem-group member of the Atelostomata close to the split of holasteroids and spatangoids. A combined analysis based on a subset of the characters employed in these two studies for the first time results in a fully resolved tree for ‘disasteroids’.Absurdaster, shows two notable morphological peculiarities: 1) it is one of the first echinoids to develop fascioles and exhibits a yet unknown type of fasciole circling the periproct, termed circumanal fasciole here; 2) it is extraordinary among echinoderms as its extraxial skeleton is reduced to a single plate, the madreporite (genital plate 2), and because its genital pores pierce axial elements rather than extraxial ones.

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

Callocystites fresti sp. nov. is characterized by an elongate theca, protuberant periproct and raised ambulacral facets. Ambulacral branching in Callocystites is isotomous, but left‐ and right‐handed branches occur because the ambulacral groove branches in the same direction twice, interrupting the regularly alternating branching to brachioles. Branching in Strobilocystites does not interrupt the alternation of brachioles and lateral food grooves always pass adoral to the first brachiole of each branch. Sphaerocystites branched as in Strobilocystites. Other morphological features suggest Callocystites, Sphaerocystites and Strobilocystites are not closely related. Callocystites has open infra‐lateral and lateral circlets and five ambulacra; Sphaerocystites and Strobilocystites have closed/modified circlets and four ambulacra. In Callocystites and Sphaerocystites the B and D ambulacra differ from the others and they have one hydropore; in Strobilocystites all four ambulacra are the same and the hydropore is double. All three genera have large, globular thecae. Ambulacral branching was a response to increased food‐gathering requirements. The following are phylogenetically informative callocystitid characters: truly open vs closed/modified plate circlets; number of pectinirhombs; number of ambulacra; presence vs absence of the ‘B D different’ pattern of primary brachioles; single vs double hydropore.In echinoderms with five ambulacra in a 2–1–2 pattern ambulacral homologies are unambiguous: the single amb is A (III). In echinoderms without this pattern or with less than five ambulacra the hydropore or a single gonopore is best for orientation. Both always occur in the CD (V‐I) interambulacrum. The position of the periproct is unreliable. Different patterns and numbers of ambulacra in Palaeozoic echinoderms render a single developmental sequence improbable. Cystoids (blastozoans) had radial water vessels in their ambulacra and added new ambulacral plates terminally. Functional morphological considerations suggest tube feet were essential for food gathering. Copyright © 2014 John Wiley & Sons, Ltd.