Problematic aspects of the form and function of the stem in Palaeozoic crinoids

Donovan, Stephen K.

doi:10.1016/j.earscirev.2015.12.006

Cited by 11 publications

(4 citation statements)

References 62 publications

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“…This is consistent with data on recent crinoids which show that the muscles are not present in the axial canal ( Holland, Grimmer & Wiegmann, 1991 ). The enlarged axial canal in early pelmatozoans is thought to be largely filled by perihaemal fluids ( Donovan, 2016 ). Thus, both hypotheses suggesting the presence of either muscles in the axial canal or MCTs on articular facet and possibility of coelom contraction are rather speculative.…”

Section: Discussionmentioning

confidence: 99%

Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural approach

Gorzelak

Zamora

2016

PeerJ

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Pleurocystitid rhombiferans are among the most unusual echinoderms whose mode of life has been long debated. These echinoderms are usually interpreted as vagile epibenthic echinoderms, moving over the sea bottom by means of a flexible stem. Although their life habits and posture are reasonably well understood, the mechanisms that control the movement of stem are highly controversial. Specifically, it is unknown whether the stem flexibility was under the control of muscles or ligamentary mutable collagenous tissues (MCTs). Here, we reconstruct palaeoanatomy of the two Ordovician pleurocystitid rhombiferans (Pleurocystites and Amecystis) based on stereom microstructure. We show that the articular facets of columnals in pleurocystitid rhombiferans are composed of fine labyrinthic stereom. Comparison with modern echinoderms suggests that this type of stereom was associated with muscles implying that their stem was a muscular locomotory organ supporting an active mode of life.

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Section: Discussionmentioning

confidence: 99%

Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural approach

Gorzelak

Zamora

2016

PeerJ

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“…1). The encrusting structures are classified as terminal dendritic radix structures composed of multiple, distally tapering, branching radicles (appendages) extending radially outward from a central, vertically oriented column (see Donovan and others, 2007;Donovan, 2016). Diagnostic features of radix structures attributable to Eucalyptocrinites include a relatively small pentalobate lumen, minute pentalobate or circular lumina within radicles, and radicles composed of discrete ossicles, sometimes surrounded by an amorphous cortex of calcite (Halleck, 1973;Brett, 1981Brett, , 1984Brett, 2015a, 2019;Plotnick and others, 2016;Poschmann, 2020).…”

Section: Typical Specimen Descriptionsmentioning

confidence: 99%

Silurian Diploporitans as Substrata:

Thomka,

Bissett,

Bantel

2023

IJES

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The middle Silurian Massie Formation of southeastern Indiana contains a rich stalked echinoderm fauna, of which diploporitan “cystoids” are a significant component. A small number of diploporitan thecae are encrusted by the dendritic radicular attachment structures of the monobathrid camerate crinoid Eucalyptocrinites. Recently, several encrusted specimens of the diploporitan Holocystites scutellatus were described from the Massie Formation of the Napoleon quarry (Ripley County) that are unusual in that the encrusting holdfasts display pronounced asymmetry with respect to radicle development. Due to settlement near the margin of the thecae, long, well-developed radicles are present on the side of the attachment structure where they could extend over the entire lateral surface of the theca, and short, poorly developed radicles are present on the side facing the margin of the theca. The anomalous nature of this attachment structure morphology is herein highlighted by comparison to more typical Eucalyptocrinites-encrusted diploporitan thecae from the same locality and stratigraphic interval. These display a much more radially symmetrical configuration of radicles due to a more central settlement position on the thecal lateral surface. Several additional morphological and paleoecological aspects of crinoid encrustation of diploporitans are described and illustrated, including an apparently bilaterally symmetrical radicle growth pattern and a rare occurrence of an encrusted Paulicystis.

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“…Within taxa that are otherwise not unusual, there may be modifications of particular structures that are extraordinary and unique, such as the contrasting arms of the mid-Palaeozoic cladids Crotalocrinites Austin and Austin, 1843, and Petalocrinus Weller and Davidson, 1896(Donovan et al 2012. And at least as extraordinary are the many bizarre forms of the stem (Donovan 2016).…”

Section: Introductionmentioning

confidence: 99%

Form and function of the strangest crinoid stem: Devonian of Morocco

Donovan

Waters

Pankowski³

2018

Swiss J Palaeontol

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Trombonicrinus (col.) hanshessi gen. et sp. nov. is a crinoid species of unusual morphology and is based solely on the stem. It comes from the (probably Lower) Devonian of Tafraoute, Anti Atlas Mountains, Morocco. It is a long crinoid stem of circular section, tapering distally throughout, with a tight curvature through 1808 between the mesistele and proxistele; attachment is distally by short, pointed, unsegmented pseudoradices. The overall appearance is reminiscent of the slide of a trombone. The dististele is essentially straight, the mesistele is more or less convoluted, and the proxistele is straight and parallels the more distal stem. The dististele was attached to an upright object around which the pseudoradices formed a close attachment. The crinoid's stem was growing down towards the substrate. The mesistele was free of the attachment surface and grew in a more convoluted manner. The proxistele was adapted to elevate the crown, growing upwards and in the opposite direction of the rest of the crinoid. This is a form unique to T. (col.) hanshessi and not recognised hitherto in the Crinoidea. The conical, most proximal part of this stem in the holotype may suggest that it was immediately beneath the cup; the specimen is considered complete apart from the crown. The loss of the crown was most likely the result of autotomy. Although the proxistele of the paratype is relatively longer, it is probably incomplete. This crinoid was either a cladid or a camerate.

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Problematic aspects of the form and function of the stem in Palaeozoic crinoids

Cited by 11 publications

References 62 publications

Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural approach

Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural approach

Silurian Diploporitans as Substrata:

Form and function of the strangest crinoid stem: Devonian of Morocco

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