Major Subgroups of Crinoidea
As mentioned above, Moore & Teichert (1978) recognized the four majorlineages that they identified as subclasses (Camerata, Inadunata,Flexibilia, and Articulata), and they placed the single species ofEchmatocrinus into its own subclass, as the primitive, basal crinoid.Revisions since 1978 include elimination of the subclass Inadunata becausethe disparids and cladids are quite separate lineages, elimination ofEchmatocrinus as a crinoid (not universally accepted), and recognition ofthe oldest Early Ordovician crinoids as the initial constructional style ofcrinoids.
In current classification hypotheses, the Cladida, Disparida,and Camerata are regarded as subclasses (Simms and Sevastopulo 1993; Ausich1998a). Simms and Sevastopulo (1993) group the Flexibilia and Articulatawithin the Cladida as a single monophyletic lineage. These relationshipsare not disputed by Ausich (1998a), but he proposes a partially paraphyleticclassification to more accurately describe the evolutionary history of theCrinoidea. Thus, the Flexibilia and Articulata are designated asmonophyletic subclasses leaving the Cladida as a paraphyletic subclass.Furthermore, the Camerata are also derived from cladids in the phylogeny ofAusich (1998a). The primitive, four-circlet crinoids are constructionallydistinctive from all other crinoids and cannot be placed within anyexisting subclass. A new subclass is erected for these forms, however italso is paraphyletic because it gave rise to both disparids and cladids(Ausich 1998b).
Five distinct groups of articulates survive in modern seas. Theirinterrelationships will be treated on a separate page. The bathyal andabyssal hyocrinids have long stalks, thin discoidal columnals, and aterminal attachment disk. The bathyal and abyssal bourgueticrinids havecolumnals articulated by synarthries (two ligament bundles flanking afulcral ridge) and attach via a terminal disk or rootlike radix. Thebathyal isocrinids have whorls of hooklike cirri along the stalk. In thebathyal cyrtocrinids, a short stalk consists of up to two columnals, or anexpanded, thickened calyx cements directly to the substrate. Thecomatulids, which occur from intertidal to abyssal depths, retain a stalkas postlarvae, but shed all but the topmost segment and take up a freeexistence as juveniles and adults.
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