A Review of Blastozoan Echinoderm Respiratory Structures

Abstract

Echinoderms have evolved diverse and disparate morphologies throughout the Phanerozoic. Among them, blastozoans, an extinct group of echinoderms that were an important component of Paleozoic marine ecosystems, are primarily subdivided into groups based on the morphology of respiratory structures. However, systematic and phylogenetic research from the past few decades have shown that respiratory structures in blastozoans are not group-defining and they have re-evolved throughout echinoderm evolution. This Element provides a review of the research involving blastozoan respiratory structures, along with research concerning the morphology, paleoecology, and ontogeny of each of the major groupings of blastozoans as it relates to their corresponding respiratory structures. Areas of future research in these groups are also highlighted.

A Silurian (Homerian) pelmatozoan echinoderm fauna from west-central Ohio, USA

“…Classification and terminology.-Class and ordinal levels of blastoids and hemicosmitoids follow Waters and Horowitz (1993) and Waters (2012), andSheffield et al (2022), respectively. Ordinal and superordinal classification of crinoids follows Cole (2017Cole ( , 2018, Wright (2017a, b), and Wright et al (2017).…”

Pleurocystites?scylla, a new species of pleurocystitid rhombiferan, and comments on early echinoderm teratologies

“…But even within Pleurocystites, P. rugeri (Paul, 1984) lacks a pectinirhomb on the B2/IL2 suture. Pectinirhombs are likely convergent structures and, as such, should not be considered as the sole diagnostic character (Sheffield et al, 2022).…”

Initial quantitative assessment of the enigmatic clade Paracrinoidea (Echinodermata)

“…3) are found in several genera (Comarocystites, Implicaticystis, Sinclairocystis, Oklahomacystis and Amygdalocystites), and there are several different types of respiratory structures found in these genera. Amygdalocystites and Oklahomacystis have paired slit-like structures that cross plate boundaries (Kesling 1968;Parsley & Mintz 1975;Sheffield et al 2022). Comarocystites and Sinclairocystis have unpaired slit structures that cross plate boundaries (Sheffield et al 2022).…”

“…Amygdalocystites and Oklahomacystis have paired slit-like structures that cross plate boundaries (Kesling 1968;Parsley & Mintz 1975;Sheffield et al 2022). Comarocystites and Sinclairocystis have unpaired slit structures that cross plate boundaries (Sheffield et al 2022). Implicaticystis has foerstepores, paired blisters situated over slits (Parsley 1978;Frest & Strimple 1982;Sheffield et al 2022) that can appear as ovular openings in thecal plates and may or may not cross plate boundaries.…”

“…Comarocystites and Sinclairocystis have unpaired slit structures that cross plate boundaries (Sheffield et al 2022). Implicaticystis has foerstepores, paired blisters situated over slits (Parsley 1978;Frest & Strimple 1982;Sheffield et al 2022) that can appear as ovular openings in thecal plates and may or may not cross plate boundaries. In paracrinoids that do not have respiratory structures, the plates do not have any openings and it is believed that those thecal plates were thin enough for gas exchange to occur through (Parsley & Mintz 1975).…”