Stylophora

Stylophora; Temporal range: Middle Cambrian - Late Carboniferous PreꞒ Ꞓ O S D C P T J K Pg N
	Cothurnocystis elizae
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Superphylum:	Deuterostomia
Clade:	Ambulacraria
Phylum:	Echinodermata
Class:	† Stylophora ; Gill & Caster, 1960
Orders
	† Cornuta ; † Mitrata ;

Last updated July 02, 2024

The stylophorans are an extinct, possibly polyphyletic group allied to the Paleozoic Era echinoderms, comprising the prehistoric cornutes and mitrates.^[2] It is synonymous with the subphylum Calcichordata. Their unusual appearances have led to a variety of very different reconstructions of their anatomy, how they lived, and their relationships to other organisms.

Stylophorans have played a major role in debates over the origin of chordates, as under the calcichordate hypothesis they were interpreted as being stem-group chordates. However, multiple lines of evidence argue against the calcichordate hypothesis, and stylophorans are now widely agreed to belong to the echinoderm total group. Debate remains over whether they are stem-group echinoderms which predate the origin of radial symmetry, or highly modified descendants of radially symmetric echinoderms.

Description

The general stylophoran body plan consists of a flattened theca and a single jointed appendage which extends from it. Stylophoran tests are composed of stereom calcite plates, which has traditionally been the basis for assigning them to Echinodermata. However, they also lack the radial symmetry characteristic of most other echinoderms, with the earlier members of the group being flattened and asymmetrical, and the later ones closer to bilateral symmetry.

In Mitrocystites and perhaps in other forms the appendage does not end in an attachment organ, and may have served the organism for movement.^[3] Cothurnocystis is asymmetrical and boot-shaped, and Mitrocystites is bilaterally symmetrical and more streamlined.

There were three major hypotheses about the anatomy and systematics of stylophorans.

The earliest idea, proposed by Ubaghs^[4] was that the group was aberrant echnoderms with a single starfish-like feeding arm. In the calcichordate hypothesis proposed by Richard Jeffries, it was suggested that some or all stylophorans might have had gill slits like chordates, and the appendage was a tail that contained a notochord.^[5] This reconstruction led to the hypothesis that some or all of the stylophorans may have been ancestral to the chordate branch of the deuterostomes, rather than being within the echinoderms.

An alternative hypothesis (proposed by D.G. Shu, Simon Conway Morris, and others) suggested that stylophorans were ecologically stalked echinoderms. The appendage was reconstructed as a stalk to attach the animal to the sea floor, but the hypothesis proposed the group was close to the ancestor of both echinoderms and hemichordates, and the stalk contained a notochord-like element or neural tube. Both hypotheses of chordate relationships were later disproven by the discovery of fossil soft tissues in a study published in 2019.^[6]

Life reconstruction of Cothurnocystis Cothurnocystis.jpg — Life reconstruction of *Cothurnocystis*

Scanning electron microscopy of preserved soft tissues in the single appendage of two genera of stylophorans showed the appendage contained an ambulacral canal with tube feet covered by mobile plates, and was not a tail or stalk with fixed plates covering a notochord or neural tube. The appendage is therefore interpreted as a starfish-like feeding arm. The enlarged base of the arm contains an extension of the body cavity rather than muscle blocks to move a tail; the structure at the base of the arm is most parsimoniously reconstructed as the mouth. Stylophorans are therefore reconstructed as true echinoderms of uncertain affiliations, without radial symmetry but with stereom and a water vascular system. The body was oriented with the arm as the anterior end of the animal, which lay on the substrate; food would have been captured by tube feet and moved down the arm to the mouth. Some genera may have also used the water vascular system for locomotion. Rather than swimming with a muscular post-anal tail as in chordates, mobile genera would have crawled "arm-first" using a water vascular system, like starfish and sea cucumbers.^[6]

Classification

There are over 120 known species of stylophoran.^[7] Stylophora is conventionally divided into two orders, Cornuta and Mitrata.^[7] Mitrates may have evolved from cornutes, which would render the cornutes paraphyletic.^[8] An alternate taxonomy regards the mitrates and mitrate-like cornutes as forming the order Ankyroida, while maintaining the order Cornuta for the less mitrate-like cornutes.^[9] The most basal known stylophoran is Ceratocystis.^[8]

Related Research Articles

<span class="mw-page-title-main">Chordate</span> Phylum of animals having a dorsal nerve cord

A chordate is a deuterostomic animal belonging to the phylum Chordata. All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa. These five synapomorphies are a notochord, a hollow dorsal nerve cord, an endostyle or thyroid, pharyngeal slits, and a post-anal tail. The name "chordate" comes from the first of these synapomorphies, the notochord, which plays a significant role in chordate body plan structuring and movements. Chordates are also bilaterally symmetric, have a coelom, possess a closed circulatory system, and exhibit metameric segmentation.

An echinoderm is any deuterostomal animal of the phylum Echinodermata, which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial symmetry, and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone. The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian.

Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are members of the largest crinoid order, Comatulida. Crinoids are echinoderms in the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. They live in both shallow water and in depths as great as 9,000 meters (30,000 ft).

Arkarua adami is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of five small dots from the middle of the disk center. Fossils range from 3 to 10 mm in diameter.

Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as asteroids due to being in the class Asteroidea. About 1,900 species of starfish live on the seabed in all the world's oceans, from warm, tropical zones to frigid, polar regions. They are found from the intertidal zone down to abyssal depths, at 6,000 m (20,000 ft) below the surface.

Cothurnocystis is a genus of small enigmatic echinoderms that lived during the Ordovician. Individual animals had a flat boot-shaped body and a thin rod-shaped appendage that may be a stem, or analogous to a foot or a tail. Fossils of Cothurnocystis species have been found in Nevada, Scotland, Czech Republic, France and Morocco.

Dipleurula is a hypothetical larva of the ancestral echinoderm. It represents the type of basis of all larval forms of, at least, the eleutherozoans, where the starfish, sea urchins, sea cucumbers and brittle stars belong. The dipleurula is a bilaterally symmetrical, ciliated echinoderm larva.

Mitrates are an extinct group of stem group echinoderms, which may be closely related to the hemichordates. Along with the cornutes, they form one half of the Stylophora.

<span class="mw-page-title-main">Deuterostome</span> Superphylum of bilateral animals

Deuterostomes are bilaterian animals of the superphylum Deuterostomia, typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia is further divided into 4 phyla: Chordata, Echinodermata, Hemichordata, and the extinct Vetulicolia known from Cambrian fossils. The extinct clade Cambroernida is also thought to be a member of Deuterostomia.

<span class="mw-page-title-main">Homalozoa</span> Extinct historic group of marine invertebrates

Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms, prehistoric marine invertebrates. They are also referred to as carpoids.

In evolutionary developmental biology, inversion refers to the hypothesis that during the course of animal evolution, the structures along the dorsoventral (DV) axis have taken on an orientation opposite that of the ancestral form.

The calcichordate hypothesis holds that each separate lineage of chordate evolved from its own lineage of mitrate, and thus the echinoderms and the chordates are sister groups, with the hemichordates as an out-group.

Stereom is a calcium carbonate material that makes up the internal skeletons found in all echinoderms, both living and fossilized forms. It is a sponge-like porous structure which, in a sea urchin may be 50% by volume living cells, and the rest being a matrix of calcite crystals. The size of openings in stereom varies in different species and in different places within the same organism. When an echinoderm becomes a fossil, microscopic examination is used to reveal the structure and such examination is often an important tool to classify the fossil as an echinoderm or related creature.

Ossicles are small calcareous elements embedded in the dermis of the body wall of echinoderms. They form part of the endoskeleton and provide rigidity and protection. They are found in different forms and arrangements in sea urchins, starfish, brittle stars, sea cucumbers, and crinoids. The ossicles and spines are the only parts of the animal likely to be fossilized after an echinoderm dies.

Cincta is an extinct class of echinoderms that lived only in the Middle Cambrian epoch. Homostelea is a junior synonym. The classification of cinctans is controversial, but they are probably part of the echinoderm stem group.

<span class="mw-page-title-main">Cornuta</span> Extinct order of marine invertebrates

Cornuta is an extinct order of echinoderms. Along with the mitrates, they form the Stylophora.

Soluta is an extinct class of echinoderms that lived from the Middle Cambrian to the Early Devonian. The class is also known by its junior synonym Homoiostelea. Soluta is one of the four "carpoid" classes, alongside Ctenocystoidea, Cincta, and Stylophora, which made up the obsolete subphylum Homalozoa. Solutes were asymmetric animals with a stereom skeleton and two appendages, an arm extending anteriorly and a posterior appendage called a homoiostele.

<span class="mw-page-title-main">Ctenocystoidea</span> Extinct clade of marine invertebrates

Ctenocystoidea is an extinct clade of echinoderms, which lived during the Cambrian and Ordovician periods. Unlike other echinoderms, ctenocystoids had bilateral symmetry, or were only very slightly asymmetrical. They are believed to be one of the earliest-diverging branches of echinoderms, with their bilateral symmetry a trait shared with other deuterostomes. Ctenocystoids were once classified in the taxon Homalozoa, also known as Carpoidea, alongside cinctans, solutes, and stylophorans. Homalozoa is now recognized as a polyphyletic group of echinoderms without radial symmetry. Ctenocystoids were geographically widespread during the Middle Cambrian, with one species surviving into the Late Ordovician.

<i>Yanjiahella</i> Extinct genus of marine invertebrates

Yanjiahella biscarpa is an extinct species of Early Cambrian deuterostome which may represent the earliest stem group echinoderm.

References

↑ Geggel, Laura (22 February 2019). "480-Million-Year-Old Mystery Creature Finally Identified from Its Preserved Guts". LiveScience.
↑ Lefebvre, B (2007). "Early Palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms". Palaeogeography, Palaeoclimatology, Palaeoecology. 245 (1–2): 156–199. doi:10.1016/j.palaeo.2006.02.021.
↑ Ruta, M (1999). "A brief review of the stylophoran debate". Evolution & Development. 1 (2): 123–135. doi:10.1046/j.1525-142x.1999.99008.x. PMID 11324028. S2CID 21968834.
↑ Ubaghs, Georges (November 30, 1967). "Le genre Ceratocystis Jaekel (Echinodermata, Stylophora)". The University of Kansas Paleontological Contributions. The Paleontological Institute, The University of Kansas. ISSN 0075-5052 . Retrieved 16 March 2023.
↑ Jefferies, R. P. S. (1986). The Ancestry of the Vertebrates. New York, NY, USA: Cambridge University Press. ISBN 978-0-521-34266-7.
1 2 Lefebvre, Bertrand; Guensburg, Thomas E.; Martin, Emmanuel L.O.; Mooi, Rich; Nardin, Elise; Nohejlová, Martina; Saleh, Farid; Kouraïss, Khaoula; El Hariri, Khadija; David, Bruno (2019). "Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes". Geobios. 52: 27–36. doi: 10.1016/j.geobios.2018.11.001 . ISSN 0016-6995.
1 2 Noailles, Fleur (2016). "Life on the seafloor: adaptations and strategies in Stylophora (Echinodermata)". Lethaia. 49 (3): 365–378. doi:10.1111/let.12152. ISSN 0024-1164.
1 2 Ruta, Marcello (2003). "A species-level supertree for stylophoran echinoderms". Acta Palaeontologica Polonica. 48 (4): 559–568.
↑ Parsley, R. L. (1997). "The echinoderm classes Stylophora and Homoiostelea: non Calcichordata". The Paleontological Society Papers. 3: 225–248. doi:10.1017/S1089332600000279.

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[1] Geggel, Laura (22 February 2019). "480-Million-Year-Old Mystery Creature Finally Identified from Its Preserved Guts". LiveScience.

[2] Lefebvre, B (2007). "Early Palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms". Palaeogeography, Palaeoclimatology, Palaeoecology. 245 (1–2): 156–199. doi:10.1016/j.palaeo.2006.02.021.

[3] Ruta, M (1999). "A brief review of the stylophoran debate". Evolution & Development. 1 (2): 123–135. doi:10.1046/j.1525-142x.1999.99008.x. PMID 11324028. S2CID 21968834.

[Ubaghs-4] Ubaghs, Georges (November 30, 1967). "Le genre Ceratocystis Jaekel (Echinodermata, Stylophora)". The University of Kansas Paleontological Contributions. The Paleontological Institute, The University of Kansas. ISSN 0075-5052 . Retrieved 16 March 2023.

[5] Jefferies, R. P. S. (1986). The Ancestry of the Vertebrates. New York, NY, USA: Cambridge University Press. ISBN 978-0-521-34266-7.

[Lefebvre2019-6] 1 2 Lefebvre, Bertrand; Guensburg, Thomas E.; Martin, Emmanuel L.O.; Mooi, Rich; Nardin, Elise; Nohejlová, Martina; Saleh, Farid; Kouraïss, Khaoula; El Hariri, Khadija; David, Bruno (2019). "Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes". Geobios. 52: 27–36. doi: 10.1016/j.geobios.2018.11.001 . ISSN 0016-6995.

[Noailles2016-7] 1 2 Noailles, Fleur (2016). "Life on the seafloor: adaptations and strategies in Stylophora (Echinodermata)". Lethaia. 49 (3): 365–378. doi:10.1111/let.12152. ISSN 0024-1164.

[Ruta2003-8] 1 2 Ruta, Marcello (2003). "A species-level supertree for stylophoran echinoderms". Acta Palaeontologica Polonica. 48 (4): 559–568.

[Parsley1997-9] Parsley, R. L. (1997). "The echinoderm classes Stylophora and Homoiostelea: non Calcichordata". The Paleontological Society Papers. 3: 225–248. doi:10.1017/S1089332600000279.

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