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

  title={Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural approach},
  author={Przemysław Gorzelak and Samuel Zamora},
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… 

Figures from this paper

A stem group echinoderm from the basal Cambrian of China and the origins of Ambulacraria
The early Cambrian metazoan Yanjiahella biscarpa is investigated, concluding that it is a stem echinoderm, is among the oldest known deuterstomes, and supports an ancestral enteropneust body plan in hemichordates.
Reply to ‘Re-evaluating the phylogenetic position of the enigmatic early Cambrian deuterostome Yanjiahella’
The interpretation and phylogenetic analysis suggest that Y. biscarpa is a stem-echinoderm, which would confirm that echinoderms acquired plates before pentaradial symmetry and that their history is firmly rooted in bilateral forms, and Zamora et al.2 raise additional questions over the interpretation of particular morphological features.
Two Coils in the Morphology of Myelodactylids (Crinoidea, Disparida): the Morphogenetic Basis of Their Formation and Adaptation Potential
The morphology of myelodactylids shows that their stem in the feeding position stretched along slightly compacted ground, resting on cirri, and the crown extended at a slight acute angle over the stem downstream, allowing them to be assigned to a new genus Imagdacrinus gen .nov.
Ecological Features of Echinoderm Distribution in the Latorp and Volkhov Regional Stages of the Lower and Middle Ordovician of the Leningrad Region
  • G. A. Anekeeva
  • Geography, Environmental Science
    Paleontological Journal
  • 2021
Abstract The systematic composition and paleoecological distribution of echinoderms in the rocks of the Latorp and Volkhov regional stages of the Lower and Middle Ordovician of the Leningrad Region
Bringing planktonic crinoids back to the bottom: Reassessment of the functional role of scyphocrinoid loboliths
Abstract. Living crinoids are exclusively passive suspension feeders and benthic as adults. However, in the past they adapted to a broad range of ecological niches. For instance, the
Scanning Electron Microscope Study of Microstructure and Regeneration of Upper Pennsylvanian Cladid Crinoid Spines
Microstructural evidence for stalk autotomy in Holocrinus – The oldest stem-group isocrinid
  • P. Gorzelak
  • Geography, Environmental Science
    Palaeogeography, Palaeoclimatology, Palaeoecology
  • 2018


Stem Structure and Evolution in the Earliest Pelmatozoan Echinoderms
Abstract Echinoderm skeletal debris from the Early–Middle Cambrian boundary Micmacca Breccia of Morocco includes the oldest known holomeric columnals. The original calcite of these ossicles is coated
Stereom microstructures of Cambrian echinoderms revealed by cathodoluminescence (CL)
The results show that the stereom microstructures widely occur in various Cambrian echinoderm clades which suggest that they likely evolved the same genetically controlled biomineralization mechanisms as those observed in modern echinoderms.
The structure of the sea lilyCalamocrinus diomedae, with special reference to the articulations, skeletal microstructure, symbiotic bacteria, axial organs, and stalk tissues (Crinoida, Millericrinida)
The skeleton of the arms and pinnules was unusual in lacking any galleried stereom; thus the ligaments as well as the muscles inserted on labyrinthic stereom may not be a sure guide to where the ligament and muscles insert, and crinoid paleontologists should use caution when reconstructing soft parts from fossil skeletons.
A New Pleurocystitid Blastozoan from the Middle Devonian of the Eifel (Germany) and Its Phylogenetic Importance
Rich echinoderm fauna from the Middle Devonian of the Eifel (Rhenish Massif, Germany) has yielded specimens of the rare recumbent pleurocystitid rhombiferans. Regulaecystis testudineus sp. nov.
The position of the edrioasteroid on the rhombiferan suggests that Amecystis was oriented with the anal side down in life and that this pleurocystitid was fully epifaunal.
Plating and pectinirhombs of the Ordovician rhombiferan Plethoschisma
New specimens showing more of the ventral surface indicate that Plethoschisma has very similar ventral plating to Deltacystis and that four of the original dorsal plate designations of PlethOSchisma were incorrect.
Findings from the Lower Devonian Hunsruck Slate clearly demonstrate that the mitrate appendage was used in locomotion and that this movement took place appendage-first, and argues against a phylogenetic position in the echinoderm crown-group.
Reassessing the improbability of a muscular crinoid stem
The findings strongly suggest that the muscles may have also been present in the stem of ammonicrinids, reassess the previous hypotheses about evolution of muscles in crinoids and provide new insights into the mode of life of Ammonicrinus.
Ontogeny in the fossil record: diversification of body plans and the evolution of “aberrant” symmetry in Paleozoic echinoderms
It is shown that most Paleozoic echinoderms are characterized by uniquely identifiable ambulacra that develop in three distinct postlarval stages, suggesting that both developmental and ecological constraints affect the evolution of novel echinoderm body plans.
New evidence for muscular articulations in Paleozoic crinoids
Evidence is provided that the microstructure of the stereom provides a reliable microstructural criterion for muscular articulation on well-preserved arm ossicles, useful in tracing the evolutionary development of flexible arm articulations in several lineages of Paleozoic crinoids.