Early phylogeny and subclass division of the Crinoidea (Phylum Echinodermata)

Abstract

A stepwise approach is employed to determine the phylogeny of the initial crinoid radiation during the Arenig and Llanvirn series of the Ordovician. Parsimony-based character analysis is completed first on Arenig crinoids and then for Arenig and Llanvirn crinoids combined.The topology from well-resolved trees of this early crinoid radiation indicates that the Crinoidea should be subdivided into six subclasses. A new subclass and new order, Aethocrinea and Aethocrinida, respectively, are proposed for crinoids with four circlets of plates in the aboral cup: lintels, infrabasals, basals, and radials. This aboral cup construction is best displayed byAethocrinus, one of the oldest known crinoids (?Tremadoc-Arenig). However, this primitive aboral cup construction is also present in two Llanvirn crinoids,PerittocrinusandTetracionocrinus.The Aethocrinea was a small, short-lived radiation of crinoids with this design that was different from those of other crinoids. Two families in the Aethocrinida are the Aethocrinidae, which includesAethocrinus, and the Perittocrinidae, which includesPerittocrinusandTetracionocrinus.In addition to the Aethocrinea, the following crinoid subclasses are recognized based on character analyses of these earliest crinoids: Cladida, Camerata, Disparida, Flexibilia, and Articulata.

The interrelationships of metazoan parasites: a review of phylum- and higher-level hypotheses from recent morphological and molecular phylogenetic analyses

“…This pattern suggests that parasites of the stalked crinoids (Cystimyzostoma from isocrinid Metacrinus) form a sister group of parasites/ commensals of the commatuloid crinoids. The phylogeny of myzostomes seems to reflect the phylogeny of their hosts (Ausich 1998). The association between myzostomes and echinoderms is very old and signs of myzostomes' parasitic activities are found on crinoid skeletons back to the Ordovician (Eeckhaut 1998).…”

Filling the Gondwanan gap: paleobiogeographic implications of new crinoids from the Castillejo and Fombuena formations (Middle and Upper Ordovician, Iberian Chains, Spain)

“…The suprageneric classification used here is from Moore & Teichert (1978) and Ausich (1998aAusich ( , 1998b. Morphological terminology follows Ubaghs (1978).…”

New insights concerning homology of the oral region and ambulacral system plating of pentaradial echinoderms

“…Generally, the skeleton of pentaradial echinoderms can be divided into axial skeleton, associated with the peristome (mouth opening) and ambulacral system, and the extraxial skeleton, comprising the rest of the body wall (Mooi et al, 1994(Mooi et al, , 2005Mooi and David, 1997, 1998, 2008David and Mooi, 1998;David et al, 2000). The UEH model strictly relates to elements of the axial skeleton of these echinoderms.…”