Two practical, illustrated, dichotomous keys to the 29 genera of living stalked crinoids are provided: one for entire animals and one for stalk ossicles and fragments. These are accompanied by (1) an overview of taxonomically important morphology, and (2) an alphabetical list by family and genus of the ∼95 nominal living species and their distribution by region. This is the first compilation of such data for all living stalked crinoids since Carpenter (1884) recognized 27 species in six genera in his monograph based on the H.M.S. CHALLENGER Expedition collection.

/pdf/artificial-keys-to-the-genera-of-living-stalked-crinoids-4vhhutbahg.pdf

Artificial Keys to the Genera of Living Stalked Crinoids (Echinodermata)

The genus Teliocrinus (Crinoidea, Echinodermata): a key taxon among pentacrinid stalked crinoids.

Aspects of functional morphology are examined and lifestyles proposed for seven exceptionally well-preserved crinoids from the Middle Ordovician Lebanon Limestone, Middle Tennessee. Potential ranges of motion are based on plate shapes, articular surfaces of attachment, and feeding structures. This diverse group of crinoids includes disparid inadunates (Columbicrinus crassus and Tryssocrinus endotomitus), a hybocrinid (Hybocrinus bilateralis), reteocrinids (Reteocrinus polki and R. variabilicaulis), and rhodocrinitid camerates (Archaeocrinus snyderi and Gustabilicrinus plektanikaulos). Using attachment structures as the basis, these crinoids can be divided into two groups: encrusters and commensals. Encrusters are the most diverse and include all taxa except the rhodocrinitids. They have a small discoidal holdfast and xenomorphic column. Proxistele-mesisteles were holomeric or pentameric. Flexure potential of this region of the column in disparids was increased by wider ligament gaps at nodal-internodal articulations; in other taxa flexure was enhanced by increasing the frequency of columnals. Short dististeles are polymeric or a plate mosaic. This region functioned as a resilient buffer between the mesistele and holdfast. Columns as a whole had moderate flexure potential. Feeding-structure design was varied, although all but Hybocrinus bilateralis had pinnulate or nonpinnulate parabolic filtration fans. Hybocrinus bilateralis had atomous arms arrayed in a bilaterally symmetrical pattern; the symmetry plane was oriented parallel to prevailing currents. Commensals in the Lebanon are the rhodocrinitids. Their attachment structures are characterized by a long distally tapering column terminating in a coil. Densely pinnulate arms formed a well-developed parabolic filtration fan.Encrusters were limited to hardgrounds or skeletal substrata. Commensals were more opportunistic, utilizing a variety of substrates, and they were widespread in Lebanon subenvironments including those with both soft and hard seafloors. Lebanon hardground assemblages are characterized by high diversity, particularly among crinoids and bryozoans. They are strikingly tiered according to elevation above the seafloor (and probably additionally by feeding limitations). This assemblage was the result of longterm coevolution in association with hardgrounds.Ontogenetic development of the column of encrusting crinoids indicates that the evolution of holomeric columnals occurred through a simpler sequence than previously proposed and need not have included gradual alignment of offset pentameres as intermediate steps. Columnals evolved from a poorly organized plate mosaic through a polymeric stage.

Paleoecology of hardground encrusting and commensal crinoids, Middle Ordovician, Tennessee

Despite being diverse globally, Miocene echinoids are poorly known from Jamaica. Moderately diverse echinoids and other echinoderms have been identified mainly from fragmentary specimens collected from chalks and mass-flow deposits of the Lower Miocene Montpelier Formation, White Limestone Group, near Duncans, parish of Trelawny. This locality has yielded the most diverse association of fossil echinoderms known from the Miocene of Jamaica, including at least ten species in four classes. This fauna is comprised of the isocrinid crinoids Neocrinus sp. cf. N. decorus (Wyville Thomson) and Isocrinus sp.; the ophiuroid Ophiomusium? sp.; the asteroids Astropecten? spp.; and the echinoids Prionocidaris? sp., Histocidaris sp., Echinometra sp. cf. E. lucunter (Linne), Echinoneus cyclostomus Leske, Clypeaster? sp. and spatangoid sp. Some echinoids are preserved as “crystal apples”. The deep water echinoderm taxa in this death assemblage suggest the depth of deposition to have been at least 200 m. At the level of genus, the echinoids of Duncans Quarry show strong similarities with coeval associations from Anguilla and Puerto Rico, although no consistent biostratigraphic marker(s) emerge from this comparison.

/pdf/lower-miocene-echinoderms-of-jamaica-west-indies-3e82ld0do4.pdf

Lower Miocene echinoderms of Jamaica, West Indies

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.

Functional morphology of synarthrial articulations in the crinoid stem

The skeletal morphology of the isocrinid crinoids Annacrinus wyvillethomsoni and Diplocrinus maclearanus

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The skeletal morphology of the isocrinid crinoids Annacrinus wyvillethomsoni and Diplocrinus maclearanus