A probable case of heterochrony in the solutan Dendrocystites Barrande, 1887 (Echinodermata: Blastozoa) from the Upper Ordovician of the Prague Basin (Czech Republic) and a revision of the family Dendrocystitidae Bassler, 1938

Abstract

The morphology of the Late Ordovician solutan Dendrocystites is reevaluated based on more than 300 specimens from the Letná and Zahořany formations (Prague Basin, Czech Republic). This genus is reported for the first time from the Bohdalec Formation, and its presence is confirmed in the Vinice Formation. The morphology of all specimens of the stratigraphically older species D. barrandei (Sandbian) is identical to that of small to medium-size individuals of D. sedgwicki (Katian). Distinctive characters of D. sedgwicki occur only in the largest specimens, and are all size-related (more asymmetrical thecal outlines, stronger ornamentation, rosetting pattern of thecal plates, proliferation of platelets in the proxistele). Consequently, the transition from D. barrandei to D. sedgwicki is interpreted as the result of heterochronic processes, with the largest individuals of D. sedgwicki displaying hyperadult morphologies (hypermorphosis). Dendrocystites is locally abundant in both the Letná and Zahořany formations, but extremely rare in the deeper deposits of the Vinice and Bohdalec formations. This pattern coincides closely with first order fluctuations of the sea-level in the Prague Basin. The life orientation and implied feeding strategy of Dendrocystites and other solutans are both critically discussed. Several independent lines of evidence suggest that solutans were more likely detritus-feeders. Finally, it is proposed that two morphologically distinct patterns of dististele organization were elaborated independently from the polyplated, undifferentiated stalk-like appendage of Coleicarpus (plesiomorphic condition). Consequently, a major subdivision of the class Soluta into two main clades (Dendrocystitida ord. nov. and Syringocrinida ord. nov.) is proposed. The monophyly of each order is supported by apomorphies based primarily on the organization of the dististele and the morphology of the periproct. "Dendrocystites" rossicus is reinterpreted as belonging to an unknown genus of syringocrinids, whereas Heckericystis kuckersiana may represent a third species of Dendrocystites. •

Laurentian origin of solutan echinoderms: new evidence from the Guzhangian (Cambrian Series 3) Weeks Formation of Utah, USA

“…The morphology of the distal extremity of the dististele in Pahvanticystis resembles the situation in Castericystis and, indeed, in many other solutans with either a distal spike or a distal hook at the tip of their homoiostele (e.g. Dendrocystoides scoticus , Maennilia estonica , the Secret Canyon undescribed solutan; Sprinkle, 1973; Jefferies, 1990; Rozhnov & Jefferies, 1996; Noailles, Lefebvre & Kašička, 2014). This small distal process suggests that an attached, post-larval pelmatozoan stage was probably not restricted to primitive solutans (e.g.…”

“…A putative gregarious mode of life is generally inferred for many Early Palaeozoic echinoderms and, in particular, for solutans and other homalozoan taxa (see e.g. Ubaghs & Robison, 1988; Lefebvre, 2007; Noailles, Lefebvre & Kašička, 2014; Martin, Lefebvre & Vaucher, 2015; Zamora & Rahman, 2015). In both Coleicarpus and Castericystis , gregarious behavior might have been related to their life-history strategy: a hard substrate was necessary for the settlement of the larvae and the fixosessile lifestyle of juveniles (see Ubaghs & Robison, 1985, 1988; Daley, 1995, 1996).…”

“…Kolata, Strimple & Levorson, 1977; Parsley, 1997; Parsley & Sumrall, 2007; Parsley, Rozhnov & Sumrall, 2012). As argued by Noailles, Lefebvre & Kašička (2014), it is very likely that all other, more basal syringocrinids (e.g. Castericystis , Minervaecystis , Plasiacystis ) form a paraphyletic assemblage.…”

<p class="HeadingRunIn"><strong>Reinterpretation of the enigmatic Ordovician genus <em>Bolboporites </em>(Echinodermata)</strong></p>

“…Although most Ordovician pelmatozoans possessed holomeric stems (i.e., formed by a single column of plates), tetra-, penta-and hexameric appendages have been also described in several crinoids (e.g., Aethocrinus moorei, Ramseyocrinus Bates, 1968;Ubaghs 1969Ubaghs , 1983Donovan 1984Donovan , 1985, as well as in some echinosphaeritid and hemicosmitid blastozoans (Jaekel 1899;Bockelie 1981Bockelie , 1982Parsley 1998). Dimeric distal stems are the rule in Ordovician solutans (Caster 1968;Ubaghs 1970;Lefebvre et al 2012;Noailles et al 2014). Although they possibly retained an attached post-metamorphic stage, Ordovician solutans were vagile and their stem did not possess any distal discoidal holdfast.…”

The origin and homology of the jointed appendages of carpoid and pelmatozoan echinoderms

“…Maennilia was lying right-side up, and the anus was to the left of the homoiostele (Rozhnov, Jefferies, 1996). Many other solutes apparently lay on the seafloor left side up (Noailles et al, 2014). Hence, after the attached larval stage, different solutes could lie on opposite sides of the theca.…”