Early stalked stages in ontogeny of the living isocrinid sea lily Metacrinus rotundus

The early stalked stages of an isocrinid sea lily, Metacrinus rotundus, were examined up to the early pentacrinoid stage. Larvae induced to settle on bivalve shells and cultured in the laboratory developed into late cystideans. Three‐dimensional (3D) images reconstructed from very early to middle cystideans indicated that 15 radial podia composed of five triplets form synchronously from the crescent‐shaped hydrocoel. The orientation of the hydrocoel indicated that the settled postlarvae lean posteriorly. In very early cystideans, the orals, radials, basals and infrabasals, with five plates each in the crown, about five columnals in the stalk, and five terminal stem plates in the attachment disc, had already formed. In mid‐cystideans, an anal plate appeared in the crown. Late cystideans cultured in the field developed into pentacrinoids about 5 months after settlement. These pentacrinoids shared many crown structures with adult sea lilies. On the other hand, many features of the stalk differed from those in adult isocrinids, while sharing many characteristics with the stalk of feather star pentacrinoids, including disc‐like proximal columnals, high and slender median columnals, synarthrial articulations developmentally derived from the symplexial articulations, limited formation of cirri only in the proximal columnal(s), and an attachment disc. On the basis of these findings, phylogenetic relationships among extant crinoid orders are discussed.     

Homology of posterior interray plates in crinoids: a review and new perspectives from phylogenetics,the fossil record and development

Despite their importance for understanding phylogeny, character evolution and classification, well-constrained homology relationships for posterior plating in crinoids have only recently been attempted. Here, we re-evaluate posterior plate homologies in all major crinoid lineages using development, fossil ontogenies and phylogenetic evidence. Based on these lines of evidence, we change terminology for some posterior plates to correct misnomers and make recommendations for updated terminology of others to better reflect homology. Among pentacrinoids (disparids, hybocrinids, eucladids, flexibles and articulates) the relative position of posterior interray plates, not their topology, reflects homology. From proximal to distal, pentacrinoid posterior plates are the radianal, anal X and right sac plate, regardless of the total number of plates in the adult calyx. Camerate posterior plating contrasts with pentacrinoids, but insufficient data are available to resolve homology relationships between these two clades. More examples of early post-larval ontogeny are needed in camerates and other Palaeozoic crinoids.     

Presumed postlarval pentacrinoids from the Lower Devonian Hunsrück Slate,Germany

Several tiny crinoids with crowns as small as 1 mm, or less, in width are newly recognized from the Hunsrück Slate of southwestern Germany. The presence of erect arms above an amorphous calyx in some specimens can be inferred. Based on comparison with the size and gross morphology of developmental stages in living crinoids, these tiny Hunsrück crinoids are judged to be at an early postlarval stage that is analogous to the pentacrinoid stage just after development from the stalked, but armless, smaller cystidean larval stage found in both living comatulids and isocrinids. Some of these tiny crinoids have a stalk up to 4 mm long attached to a now pyritized former substrate. Their clustered occurrence suggests gregarious settlement of larvae. Taxonomic identification of these presumed pentacrinoids is not possible, even to the sub‐class level, although they are preserved with larger juveniles of the cladids Propoteriocrinus and Lasiocrinus. These larger juveniles exhibit 3‐D pyritized calcite plates, whereas the probable pentacrinoids appear to be preserved as flattened, micro‐crystalline pyritized dermal tissues that enclosed lightly calcified, porous ossicles. The pentacrinoids were likely buried within weeks or months of hatching, based on developmental stages in similar‐sized living crinoids. These tiny crinoids, presumably pentacrinoids, are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely the pentacrinoid stage from one or more of the crinoid taxa (30 genera) present in the Hunsrück Slate. Assuming these are not microcrinoids, they are the first report of pentacrinoids from the fossil record and document that a Palaeozoic sister group to modern crinoids had similar developmental stages.     

Discovery of two rare species of stalked crinoids from Okinawa Trough, southwestern Japan, and their systematic and biogeographic implications

A recent submersible dive on the southern slope of Aguni Knoll, central Okinawa Trough has led to a discovery of two rare species of stalked crinoids, Proisocrinus ruberrimus and Naumachocrinus hawaiiensis, both of uncertain taxonomic affinity. The specimens of Proisocrinus ruberrimus, here termed "Moulin rouge" as a pseudonym due to its conspicuous red color, were collected from depths of approximately 1,800 m and are characterized by a long, slender stalk. The proximal columnals are pentalobate in cross section, with isocrinid-like articular facets; several bear rudimentary cirri. The following columnals lose the cirri and rapidly become almost circular; their facets bear radiating crenulations similar to those of Millericrinida. The characters observed in the proximal stalk indicate that the 'Moulin Rouge' (P. ruberrimus) belongs to the order Isocrinida rather than to the order Millericrinida. Naumachocrinus hawaiiensis was collected at a depth of 1,440 m. The long, cylindrical crown and number of arms indicate that Naumachocrinus should be classified in the Bathycrinidae.     

Pelmatozoan arms from the Middle Cambrian of Australia: bridging the gap between brachioles and brachials?

The early Middle Cambrian Monastery Creek Phosphorite (Beetle Creek Formation, Queensland, Australia) contains an assemblage of disarticulated echinoderm ossicles that are exquisitely preserved. Amongst this material we recognize pelmatozoan brachials, radials, basals and holomeric columnals. Although we cannot reconstruct the complete animal with precision, these elements represent the oldest known pelmatozoan with crinoid-like appendages. Key elements include isotomously to heterotomously branched uniserial appendage plates with a tripartite adoral food groove, a longitudinal central canal interpreted as housing entoneural nerve, and differentiated articulation facets. There are also epispire-bearing radials bearing one to four arm insertion-facets, each one pierced by a central neural canal. These canals run internal towards the oral area beneath the external food groove. Co-occuring material includes single truncated cone-shaped basals and holomeric columnals, both with a similar articulation pattern, and irregular, epispire-bearing thecal plates. This mosaic of crinozoan (uniserial isotomous to heterotomous arms with neural canal), blastozoan (epispire-bearing thecal plates, appendage leading to oral thecal food groove without direct connection with body cavity) and apomorphic characters (circumoral instead of basal entoneural plexus) is unexpected and demonstrates that crinoid-like pelmatozoans with uniserial, branched arms appeared significantly earlier than the Tremadocian, when the first articulated crinoid skeletons are found. It also raises questions about the polyphyletic appearance of feeding appendages among pelmatozoan echinoderms.     

New discoveries of Cambrian pelmatozoan echinoderm ossicles from North China

A variety of echinoderm ossicles have been discovered in the middle to upper Cambrian rocks of the North China Craton. Material was collected from two localities: Shuangqiao (SQ) section (Paibian) in Hebei Province and Linyi (LY) (Guzhangian?–Paibian?) in Shandong Province. Six types of ossicles can be recognized, including rounded thecal plates, and columnals with a narrow lumen and ridged articulating facets. The combination of characters suggests an unknown stalked echinoderm, probably an eocrinoid, with relatively advanced columnal morphology.     

The Fine Structure of the Stalk of the Pentacrinoid Larva of a Feather Star,Comanthus japonica (Echinodermata: Crinoidea)

The stalk of the pentacrinoid larva of a feather star (Comanthus japonica) is described for the first time by transmission electron microscopy. One end of the stalk bears the calyx and the other end is cemented to the substrate by attachment cement consisting of a meshwork of 5 nm filaments. The stalk is supported by a scries of skeletal ossicles pierced by a central canal: short intercolumnal ligaments connect adjacent skeletal ossicles and central through-going ligaments run the length of the central canal. At the end of the stalk nearest the calyx, the chambered organ and the closely associated axial organ are histologically similar to those of adult crinoids. Presumed neurosecretory neurons are associated with the intercolumnal ligaments, and the following kinds of nerves run down the central canal: (1) a large stalk nerve in each of the five interradii; (2) smaller coelomic nerves in each of the five radii in association with the epithelium of tubular aboral extensions of the chambered organ; (3) a very small nerve associated with the aboral extension of the axial organ in the stalk axis. This axial organ extension is surrounded by a haemal channel. Because of the small size of the stalk, none of the nerves or the haemal channel were described in previous light microscopic studies. The discussion gives special attention to the controversial motility of the pentacrinoid stalk.     

Mechanical properties of the stalk and cirri of the sea lily Cenocrinus asterius

• 1.1. The mechanical properties of the stalk and cirri of Cenocrinus asterius L. were analysed using freshly autotomized stalk segments.
• 2.2. When tested in bending, the proximal portions of the stalk had a lower flexural stiffness than the medial/distal portions. The difference between the proximal and medial/distal regions was less than an order of magnitude.
• 3.3. The rate of plastic deformation (creep) of stalk segments and cirri subjected to a constant load was used to calculate the coefficient of viscosity. Measurements taken while the samples were bathed in sea-water, distilled water, or potassium enriched sea-water produced no obvious differences in the viscous properties of the samples.

     

Columnal ontogeny in articulate crinoids and its implications for their phylogeny

Simms, Michael J. 1969 01 15: Columnal ontogeny in articulate crinoids and its implications for their phylogeny. Lethaia , Vol. 22, pp. 61–68. Oslo. ISSN 0024–1164.
Detailed doamentation of columnal ontogeny in several Lower Jurassic isocrinids reveals a number of features which are of phylogenetic significance. Columnal proportions are determined by two largely independent growth vectors. Columnal diameter is primarily a function of cup size at the time of formation, though it may subsequently undergo considerable increase through lateral accretion. Columnal height is largely independent of cup size except for a gradual increase with the growth of the whole animal. Columnal diameter increases at a much greater rate than columnal height and so columnals are relatively lower in large individuals. Heterochronous variation in vertical growth rate or the extent of lateral accretion in columnals may significantly alter their shape. The smallest isocrinid columnals found (0.35 mm diameter) have synarthrial articula. The transformation to a typical pentaradiate symplexy, via a triradiate stage, occurs at a diameter of about 0.75 mm. Synarthrial articula are unknown in millericrinid columnals, which instead have symplectial articula at small diameters (0.45 mm). The presence of synarthrial articula in the stems of juvenile isocrinids, and their absence in millericrinids. supports previous hypotheses concerning derivation of bourgueticrinids from an isocrinid, rather than a millericrinid, ancestor.     

Growth patterns and evolutionary trends of Devonian crinoid columns

The general morphology of the crinoid column is briefly reviewed; growth patterns deduced from the study of stem fragments and dissociated columnals are analysed in the two commonest groups occurring in the Devonian strata of France: the Cyclici and the Pentameri. Problems concerning the introduction of new columnals beneath the calyx and the differentiation of cycles in the proximal part of heteromorphic stems are set. Evolutionary trends affecting various morphological elements include size increase, ornamentation development, cirri insertion and distribution, epifacet regression and formation of composite and secondary holdfasts. At present, these trends appear to be limited to small systematic units but proxistelisation, defined as the downward extension of proxistele characters to the other stem regions, seems to be wide-spread in the Pentameri. The difficulty in determining the evolutionary process (neoteny, progenesis…) due to the lack of information on early ontogenetic stages is emphasized.     

Functional morphology of synostosial articulations in the crinoid column

The rarest articulation found in the crinoid column is the synostosis, in which adjacent articular facets are essentially planar. 'Synostoses' in the columns of post-Palaeozoic isocrinids are more correctly termed cryptosymplexies. comprising symplectial articulations which have become infilled by secondary calcite. Cryptosymplexial joints are totally inflexible and are the preferred sites of stem autotomy. Synostoses sensu stricto appear to have been limited to early Palaeozoic taxa, but this form of articulation was soon succeeded by the symplexy. Synostoses were probably commonest in meric columns which evolved from hohlwurzels and in which the main flexibility was along meric sutures, rather than between columnals. With the evolution of the holomeric columnal. a more flexible articulation between columnals was a functional necessity in order that the stem did not develop into a stiffened rod. The solution was the evolution of the symplexy. *** Crinoids, columnals. synostosis, functional morphology evolution.     

Larval development of the featherstar Aporometra wilsoni (Echinodermata: Crinoidea)

Abstract. Larval development of a small ovoviviparous comatulid crinoid, Aporometra wilsoni , was investigated using a population from South Australia. The genital pinnules of reproductive females each contain an ovary, within which are oocytes of various stages. Generally, one or more developing larvae lie outside the ovary, but within each pinnule. Larvae pass through "uniformly ciliated" and doliolaria stages before they exit the pinnule via the genital pore. The doliolariae lack the usual ciliary bands and are unable to swim. Doliolariae dissected from pinnules were followed through metamorphosis to the cystidean stage until the pentacrinoid larval stage. While previous reports on Aporometra have noted pentacrinoids attached to the female, virtually no pentacrinoids were found attached to any of the hundreds of adult females observed during this study. Females sampled from the mid-reproductive season (September and October) were found to bear >2500 developing eggs and larvae at a time. It appears that emerging doliolariae fall from the female and attach to other substrates to complete development. Aporometra is classified in Notocrinida with the Antarctic crinoid Notocrinus. This classification is based in part on their supposedly homologous larval brooding. However, the reproductive mechanism in A. wilsoni is quite different from Notocrinus , calling into question their current status as sister taxa.     

Crinoid stalk flexibility: theoretical predictions and fossil stalk postures

Flexibilities in Lower Mississippian crinoid stalks were inferred from preserved postures and shown not to conform with predictions of a cantilever beam model. Flexibilities were not correlated with hard-part characters such as stalk diameter, stalk length, or columnal height. The lack of correspondence between the predictions of the cantilever model and observed flexibilities implies that the most likely control of stalk flexibility is the ligament, more specifically, its non-constant, mutable properties. Although a few Lower Mississippian crinoids, such as Gilbertsocrinus, Platycrinites , and Camptocrinus , have enhanced flexibility achieved by radical modifications of columnal facet morphology, this study has failed to identify any general morphological characters that consistently predict flexibility. It appears that skeletal morphology is a poor guide to stalk flexibility; mutable collagenous tissue is the key. Crinoidea, taphonomy, constructional morphology, Lower Carboniferous, connective tissues.     

Functional morphology of synarthrial articulations in the crinoid stem

Synarthrial fulcral ridges are found in crinoid columnals from the mid-Ordovician to the present and in all four subclasses. Similar articulations did not become common in the cirri until the Mesozoic. Synarthrial stem articulations fall into two broad groups. Type I articulations have a fulcral ridge in the centre of the articular facet. In elliptical ossicles this ridge corresponds to either the long (IA) or short (IB) axis of the facet. Although both are functionally similar, Type IA ossicles are more common. Type II articulations have an excentric fulcral ridge, parallel to either the long (IIA) or short (IIB) axis of the articular facet. Type IIA articulations are found in crinoid stems capable of coiling. Type II articulations are particularly common in the cirri of articulates and are well adapted for attachment to hard and soft substrates. Columnals with Type I articulations often have divergent fulcra, giving the stem flexibility in all directions, but this feature is not seen in cirri or in coiled stems, where it would impair normal functions. Only the cirri of isocrinids and comatulids are muscular, so the movement of columns with fulcra must be passive.     

Hrabalicrinus zitti gen. et sp. nov., and other Upper Jurassic crinoids (Echinodermata,Crinoidea) from the Brno area (Czech Republic)

Jurassic (Oxfordian) crinoids from the Brno area (Czech Republic) are described in details for the first time. A rich crinoid assemblage consisting of cups, isolated cup elements, brachial plates, columnals, pluricolumnals, and cirrals is assigned to isocrinids Isocrinus amblyscalaris (Thurmann), Balanocrinus subteres (Münster), B. pentagonalis (Goldfuss), Isocrinida indet., comatulid Hrabalicrinus zitti gen. et sp. nov., cyrtocrinids Lonchocrinus sp., Cyrtocrinus cf. nutans (Goldfuss), Pilocrinus moussoni (Desor), Tetracrinus moniliformis Münster, Cyrtocrinida indet., and millericrinids (Millericrinida indet.). Crinoids already mentioned from the Jurassic strata of the Czech Republic are subsequently revised. Apart from the isolated remains of Isocrinida, Millericrinida, and Thiolliericrinida, the presence of any other taxon reported from this area should be treated with extreme caution. A rare example of non-regenerative columnal healing (the so-called callus) in I. amblyscalaris is also described. Based on sedimentology and microfacies, the Jurassic limestones were deposited in various palaeoenvironments of upper carbonate platform and shelf lagoon (0 to > 50 m palaeodepth).     

The behavior and the morphology of sea lilies with shortened stalks: implications on the evolution of feather stars

Extant crinoids can be divided into two groups, stalked sea lilies and stalkless feather stars. Feather stars are considered to have evolved from stalked ancestors by losing most of the stalk, but other differences are present between the two groups. The unsegmented centrodorsal, long and curved cirri near the crown, small calyx, and the ability to swim are all feather star features not found in the sea lilies. To figure out which of the above features evolved directly correlating with loss of the stalk in feather stars, we cut off the stalk from the sea lily Metacrinus rotundus and kept them alive in an aquarium. The specimens with shortened stalks were able to stand and crawl with their arms without the support of their stalks, but swimming was not observed for any of the animals. Morphologically, neither fusion of the remaining segments nor the reduction of the size of the calyx were observed, but the cirri became long and curved near the crown. Therefore, the extant sea lilies possess a potential to adapt to incidents of stalk loss. Specimens autotomizing most of their stalks were observed, suggesting that the potential is actually employed in nature. This mechanism linking the reduction of the stalk and the changes in the morphology of cirri may have played an important role in the evolution of the feather stars, if the stalked ancestors of feather stars also possessed this potential. Experimental zoological approaches as this study may provide new insights to the questions of evolution.     

A new type of stalk articulation in the sea lily genus Vityazicrinus (Echinodermata,Crinoidea) and its ontogeny

A new stalk articulation named pseudo-synarthry is here described from the mesistele of Vityazicrinus petrachenkoi, a rare deep-sea crinoid from the Central Pacific Ocean. Pseudo-synarthries have an articulation facet displaying a general structure closely resembling the morphology of the true synarthry, i.e., with a strong bilateral symmetry and deep ligament depressions. Pseudo-synarthries differ from synarthries in lacking a hinge-like fulcral ridge and developing two additional depressions bordered by prominent crescent ridges at opposite sides of the bilateral symmetry axis. Pseudo-synarthries develop in the mesistele below a proxistele articulated by symplexies of 6–8 crenular units. Distally, subsidiary radial ridges appear on the outer edge of ligamentary depressions and tend to multiply, transforming pseudo-synarthries into multiradiate syzygies, as previously observed in the genus Guillecrinus. A chaotic polymeric pattern locally appears in the proxistele and mesistele, which tends to develop into a holomeric pattern during growth, devoid of any visible trace of ossicle fusion. Both early columnal ontogeny in comatulid larvae and the transition from a polymeric to a holomeric pattern in the guillecrinid stalk lead to the rejection of the hypothesis that the monomeric columnal results from the fusion of pre-existing ossicles. Among Guillecrinidae, pseudo-synarthries constitute derived characters that are unique to the Vityazicrinus mesistele. The development of radial subsidiary ridges in the distal stalk corresponds to a synapomorphy shared by Vityazicrinus and Guillecrinus, the two only genera currently attributed to this family. Pseudo-synarthries in Vityazicrinus appear as advanced stalk articulations adapted to the deep-sea environment, which are unknown from the fossil record.     

Direct development of the brittle star Amphiodia occidentalis (Ophiuroidea, Amphiuridae) from the northeastern Pacific Ocean

Abstract. The highly modified development of the brittle star Amphiodia occidentalis is described from post-fertilization to the juvenile stage. Fertilized eggs are negatively buoyant, ∼190 μm in diameter, surrounded by a thick hyaline layer and a tough fertilization envelope. After gastrulation, embryos flatten into a bilaterally symmetrical disk with a U-shaped ridge surrounding an indented stomodeum on the oral surface. Internally, a ring of ∼22 calcitic ossicles grows at the edge of the disk. Vestigial ophiopluteal structures such as a ciliated band, paired larval spicules, or larval arms are not expressed during development. Although the fertilization envelope disintegrates on day 3, developmental stages remain immotile for five more days until they move with podia. At hatching, five hydrocoelic lobes are evident on the left side of the post-gastrula, and these migrate clockwise around the stomodeum, establishing pentamerous radial symmetry. Central and radial plates originate on the right side and migrate to a dorsocentral location as pentamerous symmetry is established. Development of the juvenile oral skeletal frame follows closely that described by Hendler (1978) for Amphioplus abditus except that A. occidentalis did not form buccal scales. The juvenile mouth opened by day 12. Fifty-five days after fertilization, juveniles had not added their first arm segments, although the first lateral arm plates had appeared. Developmental stages identical to those described here have been found in plankton tows taken in Oregon usually after storms that bring high waves. The unusual development of this species probably occurs in both benthic and pelagic environments.     

Cyrtocrinids (Cyrtocrinida,Crinoidea) and other associated crinoids from the Jurassic (Kimmeridgian–Tithonian)–Cretaceous (Berriasian–Barremian) of the Carpathian Foredeep basement (western Ukraine)

Upper Jurassic (Kimmeridgian–Tithonian) and Cretaceous (Berriasian–Barremian) strata of the Ukrainian part of the Carpathian Foredeep basement are rich, at least locally, in crinoid remains. Crinoids belonging to cyrtocrinids (Cyrtocrinida) are represented by whole cups, isolated remains of disarticulated cups, brachial plates and columnals. They are assigned to the following taxa: Cyrtocrinida indet., Eugeniacrinites cf. cariophilites (von Schlotheim), Lonchocrinus sp., Phyllocrinus stellaris Zaręczny, Ascidicrinus pentagonus (Jaekel), Gammarocrinites sp., Psalidocrinus armatus (Zittel), Psalidocrinus sp., and Hemibrachiocrinidae gen. indet. Cyrtocrinids are associated with other stalked (isocrinids, Isocrinida and millericrinids, Millericrinida) and stemless (saccocomids, Roveacrinida) crinoids. Columnals, pluricolumnals, brachial plates, and cirrals of isocrinids are assigned to Balanocrinus sp., Isocrinina fam. et subfam. indet., and columnals of millericrinids to Millericrinida indet. Free-living roveacrinids are assigned to Saccocoma sp. and Crassicoma sp. Knowledge on Jurassic and Cretaceous crinoids formerly described from Ukraine is discussed. Although majority of crinoids described herein seems to be allochthonous, autochthonous forms were also found with certainty in some intervals. These include some cyrtocrinids, which dominate in shallow-water environments of the Ukrainian Carpathian Foredeep basement. Isocrinids are also common in this shallow marine environment, whereas sessile saccocomids are assigned to low-energy, mud-supported bottom, open marine, outer-platform/upper slope, and relatively deep environments.     

Description of juvenile development ofArtediellus neyelovi (cottidae) from off Usujiri, southern Hokkaido, Japan

Juveniles ofArtediellus neyelovi are described on the basis of 24 specimens (8.3–23.6 mm SL) from Hokkaido, Japan. All medial and paired fins were completely developed in all specimens. The smallest specimen (8.3 mm SL) had a slender elongated suborbital stay similar to that of adults. Specimens 8.3–10.1 mm SL had 4 preopercular spines, cirri absent on the head and body, except a very small supraorbital cirrus, and sensory canals comprising open grooves restricted to the head surface. Specimens 14.1–20.0 mm SL had complete cephalic sensory canals, and the 2nd and 3rd preopercular spines reduced. Specimens 20.8–23.6 mm SL had a nearly complete lateral line canal and exhibited most specific diagnostic characters except some cephalic cirri. The anterior 3 neural arches on both sides were separate at 8.3 mm SL, but had become fused (except for the anteriormost) at 14.3 mm SL. The anteriormost arch was not fused in an adult, 71.3 mm SL. Some juveniles had very reduced bony plates under the skin anterodorsally on the body, which were not present in adults.